Version 2.0, 31 July 2006
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Lt Colonel David E. Bowles and Colonel James A. Swaby
USAF Institute for Operational Health
2513 Kennedy Circle Drive
Brooks City-Base, TX 78235
This guide is intended to be a primary and expeditious information source for aiding deployed military personnel in the initial steps of pest identification related to surveillance and public health matters associated with invertebrates of medical importance. It is not intended to be a definitive or exhaustive treatise on the subject material. Furthermore, the contents of this manual represent only a compilation of the available literature, and it is not intended in any fashion to represent an original research paper. This document is intended to be a starting point for obtaining information and not an end point. Readers seeking additional information on a particular topic addressed herein should refer to the referenced material or other sources of information as appropriate.
Treatment guidelines, where presented, are based on current available information at the time this document was written. Practitioners have the sole responsibility to ensure the correct dosages of medicines are provided, and they also should ensure correct treatment regimes by consulting the most recent appropriate information sources.
Use of trade or brand names in this publication is for the sole purpose of illustration and does not imply endorsement by the United States Air Force.
THIS FIELD GUIDE IS INTENDED FOR USE BY MILITARY AND CIVILIAN EMPLOYEES OF THE UNITED STATES DEPARTMENT OF DEFENSE ONLY AND IS NOT AUTHORIZED FOR PUBLIC DISSEMINATION OR SALE IN ANY FORM
Types of negative interactions with arthropods
Delusory Parasitosis and Entomophobia
Dangerous Invertebrates of Military Importance
Black widow spiders and their relatives
Other potentially dangerous spiders
Treatment of envenomation by scorpions
Other medically important mites that bite people
Other flies that cause myiasis
Squids, octopuses and cuttlefishes
Snails as hosts of schistosomiasis
The purpose of this guide is to present the reader with a basic yet sound understanding of the dangerous types of invertebrates that may be encountered during military operations worldwide. Brief descriptions of the physical and behavioral characteristics of these animals are presented. This field guide only considers those animals which pose a threat from direct contact and does not address toxic responses from food or contact allergies, or consumption of certain poisonous animals. In addition, a few invertebrates are included here not because they present a danger to people, but because they are often incorrectly presumed to be dangerous.
A considerable amount of literature was reviewed, digested and consolidated to create this field guide. In an effort to make a concise guide with streamlined text to facilitate ease of reading under the operational conditions it was intended to serve, individual information sources have not been cited in the text. To the maximum extent possible the information extracted from these references has been paraphrased. Some suggested references for obtaining additional information on these animals are included at the end of this document.
An attempt was made to use common language in this document to describe symptoms associated with arthropod attacks. However, for the sake of brevity in some situations, or where specific terms were essential to avoid confusion, we used medical and technical terminology. Those terms are defined in Appendix 1.
Threats from invertebrates encompass two broad categories: point source threats and psychological threats. Point source threats are those that can cause physical injury or death in a brief period of time. The sting of a wasp, and transmission of deadly disease agents are two examples of point source threats. Psychological threats, by comparison, are those that do not kill or directly threaten health, but rather present unpleasant situations for people to the extent that routine functioning is impaired. Both point source and psychological threats have the real potential to disrupt or even halt military operations, and they present serious concerns that commanders and the military medical community must address during both peacetime and contingencies.
There are several types of potential negative interactions associated with invertebrates including physical pain, disease, envenomation, myiasis, allergic reactions, psychological disorders, and death.
Physical pain- Bites, piercings, and stings caused by a wide variety of invertebrates can produce varying amounts of suffering among victims. Symptoms can range from mild annoyance to incapacitation. Although such physical trauma generally is not lethal, it may render a victim incapable of normal activity, and it can result in psychological disturbance among certain individuals.
Disease- Transmission of arthropod- or vectorborne disease agents represents the most substantial and continuous non-combat threat to military members during deployments. The World Health Organization has estimated there are 10 million cases annually of vectorborne diseases worldwide with many being fatal. Historically, vectorborne diseases have produced far more morbidity and mortality (greater than 60%) among U.S. military forces during modern wars than battle injury and non-battle injury combined. In addition, vectorborne disease epidemics can serve as a severe detriment to force morale.
Envenomation, the injection of venom into the body through either bites and/or stings, is perhaps the most rapid and immediate deleterious response invertebrates can inflict on humans. The response of such envenomations can range from mild irritation and limited necrosis of tissue to systemic failure and death. The venoms producing these conditions are broadly grouped as either neurotoxic or necrotic. Neurotoxic venoms are those that negatively affect the nervous system while necrotic venoms are those that destroy blood and tissue. Occasionally, the venom of some invertebrates contains both neuotoxic and necrotic properties. In addition to injecting venom, some caterpillars and beetles produce toxins that cause dermatitis when contacted.
Myiasis is the invasion of the tissue of man or animals with the larvae (maggots) of certain flies (Diptera) that consume flesh or body fluids for sustenance. Such invasions may be benign or even asymptomatic, or they may result in more destructive disturbances. Myiasis is often described in terms associated with the site of entry. Types of myiasis recognized in humans include urogenital, gastrointestinal, ocular, auricular, and cutaneous which is the traumatic invasion of tissue and the most significant form of myiasis. Most instances of myiasis are accidental or opportunistic (facultative) rather than obligate. Although flesh-eating dipteran larvae can be successfully used to debride necrotic tissue from wounds under controlled medical conditions, myiasis under operational conditions potentially can damage healthy tissue and produce severe psychological distress in victims. When wounds are involved, the term “traumatic” may be applied, and when the lesion is boil like, it is referred to as furuncular myiasis. When larvae burrow in the skin in such a way that the progress may be followed as the larva advances, the term “creeping myiasis” (creeping eruption) is applied. Myiasis has tremendous potential for psychological disturbance among afflicted military personnel.
Urtication is a physiological response to contact with toxins of certain invertebrate body parts, such as the setae of certain moth larvae, and nematocysts (stinging cells) of jellyfish and corals. Urtication can cause a painful burning and itchy skin eruption, or hives, at the point of contact. Although rarely fatal, urtication can be debilitating and may result in systemic shock in some individuals.
Allergic Reactions occur primarily through contact with venom, saliva, or certain body parts of invertebrates such as setae. Reactions can be either localized (wheals, swelling) or systemic (anaphylactic shock), and the range of severity, including death, is broad.
Delusory Parasitosis and Entomophobia are psychological disorders stemming from contact with insects and their relatives. Psychological threats posed by invertebrates often are cumulative in their effect. In other words, the more experience an individual has the greater the negative impact on health and welfare. The importance of such cumulative encounters is a function of the number and diversity of pests in an area, the quality of living conditions, ability to escape the pests, fatigue, and stress. Under certain conditions, such as an extended deployment, nuisance pests can become a more substantial threat to mission success than disease, especially when pest densities are high and disease incidence is low. Delusory parasitosis often is an intensely emotional psychological disorder characterized by the unfounded belief that parasites, usually insects, are living on or in the body. This condition, although very rare, can become sufficiently severe in some individuals to be incapacitating, and these individuals often require professional mental health care. Entomophobia, by comparison, is simply an irrational fear of insects and their relatives, or the damage or diseases they are capable of inflicting. For example, some individuals may develop an irrational fear of bees after being stung. The primary difference between entomophobia and delusory parasitosis is that the former occurs only in the presence of certain insects while the latter encompasses a near constant state of agitation and distress.
Pesticides for controlling vectors and pests should be applied only by qualified pest management personnel. Department of Defense guidance on pesticide selection and integrated pest management can be found in the Contingency Pest Management Guide (Technical Guide No. 24, Armed Forces Pest Management Board), and Guide to Operational Surveillance of Medically Important Vectors and Pests (“Operational Entomology”) available from the USAF School of Aerospace Medicine. Additional information and instruction on pest management issues of military importance can be found on the website of the Armed Forces Pest Management Board (www.afpmb.org).
Personal Protective Measures Against Arthropods
Guidance on personal protection from arthropods and other invertebrates can be found in Personal Protective Measures Against Insects and Other Arthropods of Military Significance (Technical Guide No. 36, Armed Forces Pest Management Board), and Guide to Operational Surveillance of Medically Important Vectors and Pests (“Operational Entomology”). Additional information and instruction on personal protection from arthropods can be found on the website of the Armed Forces Pest Management Board (www.afpmb.org).
Dangerous Invertebrates of Military Importance
Appendix 1 contains a list of the dangerous invertebrates of military importance including their geographic distributions.
(Spiders, Scorpions, Ticks, Mites, Camel Spiders)
Envenomation by arachnids causes significant medical illness worldwide. Among the most important groups of spiders are the widow spiders (Latrodectus spp.), recluse spiders (Loxosceles spp.), the Australian funnel web spiders (Atrax and Hadronyche spp.) and the wandering or banana spiders (Phoneutria spp.) of Brazil. Scorpions are widely distributed worldwide, but only a few species primarily distributed in Africa, the Middle East, and Latin America can inflict fatal stings. However, scorpion stings represent the most important source of arachnid envenomation in many of these areas occasionally causing morbidity among adults and death among children. Ticks and mites are notorious vectors of serious human disease and irritation. Finally, some arachnids such as camel spiders may be harmless if left alone, but their appearance can cause psychological distress among people.
The vast majority of the approximately 25,000 species of spiders known worldwide are completely harmless to people. However, a few species are capable of causing substantial pain, suffering, and even death to their victims. Even the potentially dangerous species are shy and secretive, and contact with them is normally accidental. Because of the difficulty in accurately identifying spiders, all types should be avoided.
Some banana spiders (Phoneutria fera, Phoneutria ochracea, Phoneurtria spp.) distributed in South America are aggressive and have been implicated in human envenomations leading to death. These spiders are also commonly referred to as wandering spiders in South America, but they are not related to the wandering spiders of Africa. Banana spiders do not spin a web. These spiders bite hundreds of South Americans yearly and most often during the winter months. The bites are painful, and after a few hours, the pain becomes deeply seated and generalized, and the area around the bite becomes swollen. The venom is a potent neurotoxin that affects both the central and peripheral nervous system. Envenomation may involve a variety of symptoms including altered pulse rates, irregular heartbeat, temporary blindness, sweating, fever, and increased glandular functions, especially the kidneys. Roughly 24 hours following the bite, the victim may suffer from general muscle pain and prostration. Fatalities are not common and children under 6 years of age are the most vulnerable. There is no antivenom available, and treatment may include use of analgesics and antihistamines although they are not always effective.
Figure 1. Banana spider (Phoneutria fera), South America. Photo: Danne Rydgren.
Black widows spiders and their relatives
Black widow spiders and their relatives (Latrodectus spp.) are among the most dangerous spiders to humans. Although timid and reclusive in behavior, they can inflict painful and potentially deadly bites when provoked or accidentally contacted. These spiders often are shiny black in appearance and approximately one inch or less in body length. Most widow spiders have the ventral (bottom) side of the abdomen is variously marked with red spots or other shapes, and some species may also have similar markings on the dorsum (top side). The red hourglass marking of the southern black widow, Latrodectus mactans, in North America, and the red dorsal spot of the redback, Latrodectus hasselti, in the Austro-Asian region are perhaps the most well known of such markings among these spiders. Approximatley 40 species of “black widows” occur worldwide. Medically important species occur in the Middle East, Europe, Madagascar, Africa, Asia, Australia, and throughout the Western Hemisphere. Geographically unique common names applied to the black widows include shoe-button spider (South Africa), katipo (New Zealand), redback (Australia), and malmignatte and karakurt (Europe). Other species of Latrodectus of concern that are not black in color include the brown widow (tropical areas worldwide; common in the southern United States), red widow (central and southern Florida, Africa), and northern widow (northern Florida to Canada).
Figure 4. Red back (Latrodectus hassleti), Australia. Photo: source unknown.
Figure 5. Brazilian black widow (Latrodectus curacaviensis), South America. Photo: source unknown.
Figure 6. African black widow (Latrodectus indistinctus), South Africa. Photo: source unknown.
Figure 7. Red widow, (Latrodectus bishopi). Photo: source unknown.
Figure 8. Brown widow (Latrodectus geometricus). Photo: Invasive Species Council.
Figure 9. Brown widow (Latrodectus geometricus). Photo: F. J. Santana.
Although bites from black widows are relatively rare, and the toxicity of their neurotoxic venom varies widely, envenomation by these spiders can be dangerous. Widow spider bites can cause a clinical condition referred to as latrodectism. The most significant feature of latrodectism is severe and persistent pain, although some bites may cause only minor effects. Although the bite itself is often painless initially, significant systemic symptoms may ensue in a matter of minutes, beginning with severe localized pain of increasing intensity that may become generalized. Symptoms include severe muscle pain, rigid “boardlike” abdominal cramping, tightness through the chest, difficulty breathing, and nausea. The dermatologic responses of Latrodectus bites may be mild, and include localized redness of the skin, sweating, and erection or bristling of hair at the wound site within the first half hour. The nodes draining the wound site may become palpable and painful. In addition, cyanosis may develop around the bite site and there may be various dermatological eruptions such as hives or itchy wheals. Although death is rare, mortality can be 4-5% without treatment. Bite victims usually require medical treatment, including antivenom for non-sensitive individuals, and hospitalization. Black widow bites have been occasionally misdiagnosed as ruptured ulcers, acute appendicitis, kidney problems, or food poisoning.
There are several commercially available widow spider antivenoms. These antivenoms include those for the black widows (L. mactans, L. indistinctus) of North America (Merck), the red-back spider (L. hasselti) in Australia, and brown widow (L. geometricus) spiders of South Africa, the Argentinian L. mactans, and the Mexican widow spider. European widow spider (L. tredecimguttatus) antivenom is no longer produced. Although these antivenoms produce few allergic responses, and they have been shown effective under laboratory conditions in addition to having cross-reactivity between many species, they are seldom used. Treatments for envenomation by black widows may include use of antivenom for high-risk patients, but muscle relaxants such as calcium gluconate, magnesium sulfate, and diazepam are more commonly used treatments. Historically, an effective treatment included use of muscle relaxants and an intravenous solution of 10% calcium gluconate. Recommendations for pain control include intravenous morphine sulfate for severe cases and aspirin and acetaminophen for milder envenomations.
Brown recluse spiders (Loxosceles spp.), also known as fiddlebacks, are widely distributed throughout the world with over 100 described species in the genus. Envenomation by some of these species has well documented dangerous effects on people. Not all of the known species have been shown to be dangerous, but it is possible that many pose a potential health threat to people. Antivenoms are available for Loxosceles spp., but there is little evidence to support their effectiveness, particularly against local effects. The known and potentially dangerous species of Loxosceles are shown in Appendix 1.
Figure 11. Brown recluse (Loxosceles reclusa), North America. Photo: David Bowles & Mark Pomerinke.
Figure 12. Loxosceles valida, South Africa. Photo: Museums of Cape Town.
The fiddle-shaped mark on the cepahalothorax, long legs and sleek, brown to gray coloration are characteristic of all members of this genus. However, the fiddle-shaped mark is not well defined in some species. Loxosceles reclusa, a North American species, is perhaps the most recognized species in this group. The Chilean recluse, Loxosceles laeta, and the Mediterranean recluse, Loxosceles rufescens have been introduced to the United States, Canada, and likely other areas of the world as well. Although some of these introduced populations are thought to have been exterminated, others almost certainly have become naturalized and continue to exist. Generally, these spiders are shy and reclusive by nature, but they will bite when harassed or accidentally contacted, and multiple bites are not uncommon.
Considerable myth and misinformation surround the bites of brown recluse spiders. Many “bites” by these spiders reported by physicians are misdiagnosed, and the “bite” is often due to other factors. In reality, brown recluse bites are rare relative to their population densities in structures shared with people. Most bites by brown recluses are asymptomatic or self-resolving. Although the bite of a brown recluse produces little pain initially, the potent necrotic venom is capable of rapidly destroying living human tissue around the bite site. This phenomenon is known as necrotising arachnidism syndrome, but it occurs in only about 10% of victims. Approximately 12-24 hours following envenomation, the area around the bite site becomes painful and swollen, the skin becomes reddened or mottled purplish-red, there may be some areas of hardened tissue, and a blister or pimple may form. In certain cases, there is further progression of the venom’s action to include, a light-colored halo around the bite site with the central area appearing gray-blue in color, and the surrounding area become reddened. When these later symptoms appear, the patient will often develop deep tissue necrosis, and a typical lesion is about the size of a dime or smaller, raised around the edges and sunken in the center. While some bite victims do not show any reaction the range of responses in those that do varies from a small pimple-like lesion, to severe, full tissue necrosis and formation of ulcers that may take months to heal or require surgical intervention. Rarely, additional systemic reactions may occur including disseminated intravascular coagulation, passing blood in the urine, acute kidney failure, convulsions, coma, and rarely death.
Figure 15. First day response in a patient bitten by a brown recluse. Photo: source unknown.
Treatment for brown recluse bites can include, to the extent possible, immediate immobilization and elevation of the affected area and use of cold compresses. Under direct care of a physician, analgesics can be used for pain relief, and the victim should have a tetanus booster when necessary. Corticosteroids can be injected into the bite wound to reduce pain and inflammation. Also, 100 mg of Dapsone given daily can limit cutaneous necrosis. Systemic antibiotics may be used to treat secondary infections. In extreme cases of necrosis, surgical excision of the wound and skin grafts may be necessary, but only after the necrosis has completely stopped.
Roughly 35 species are known among the genera Atrax and Hadronyche, the Australian funnel web spiders. Funnel web spiders are of moderate size with some species approaching 1.5 inches (40 mm) in length. Several of the funnel web spiders are known to envenomate humans with serious consequences, and bites of some species can be fatal. The genus Atrax is distributed in eastern and southern Australia and New Zealand, while Hadronyche is generally distributed throughout Australia and Tasmania. The distribution of Atrax robutsus (Sydney funnel web spider) is restricted to an area in a radius of approximately 100 miles (160 km) around Sidney, Australia. Atrax robustus and Atrax formidabilis arguably are the most venomous and dangerous spiders in the world. Several species of funnel web spiders have very serious bites, but there have been no reported fatalities. Less than a couple of dozen human deaths from funnel web spider envenomations have been recorded since the 1920’s.
Figure 17. Funnel web spider (Atrax robustus) Australia. Photo: Danne Rydgren.
Figure 18. Funnel web spider in a defensive posture with fangs exposed. Photo: Marc Birat.
Unlike black widows where the bites of males are inconsequential, the neurotoxic venom of male funnel web spiders is much more virulent than that of the female even though the female secretes larger quantities of venom. Females normally have a limited territory while the males wander about seasonally searching from females. Thus, wandering males are responsible for the majority of bites attributed to these spiders. One unusual aspect of funnel web venom is that it appears to be toxic only to primates (monkeys and humans) which lack a naturally occurring inhibitor. When attacking, funnel web spiders grip the victim and bite repeatedly.
Reactions to envenomation by funnel web spiders includes skeletal muscle spasms and twitching, weakness, excessive salivation and sweating, bristling of hairs, rapid heartbeat, high blood pressure, irregular heartbeat, abdominal pain, nausea, vomiting, pulmonary edema, leaking of capillaries, kidney failure, unconsciousness, shock, and death. Once injected, venom can reach the circulatory system in as little as 2 minutes, and death can result in as little as 15 minutes, but fatalities can occur up to 3 days following the bite. Antivenom for the various dangerous funnel web spiders is available in Australia.
The hobo spider (Tegenaria agrestis) was introduced to the United States from Europe and has been implicated in human envenomations in the Pacific Northwest, Alaska, and Idaho, and additionally throughout their natural distribution. Symptoms include a slight prickling sensation following the bite and a small insensitive hard area that appears within 30 minutes surrounded by an expanding reddened area of up to 6 inches in diameter. This area will become blistered between 15 and 35 hours after the bite, and, about a day later, the blisters break and ooze. Necrosis sometimes continues even after the wound starts to scab over. The necrotic lesion can vary from 1/2 to 1 inch (12-25 mm) or more in diameter and may take several months to heal. Painful headaches also have been associated with hobo spider envenomation. An effective antivenom is available for treating bites of this species, but it is not given to all patients.
Figure 19. Hobo spider (Tegenaria agrestis). Photo: Maxence Salomon.
Harpactirella lightfooti of South Africa is a large spider that is seldom encountered by most people, but the severity of their bites makes them of medical interest. One of the most distinguishing features of these spiders is that their spinnerets are very long and protrude well beyond the posterior margin of the body. The body length may exceed 30 mm. and the body and legs are thickly covered with brownish-gray hair-like setae. The exact distribution of H. lightfooti in Africa is not well established, but it appears to be restricted to the Southwestem Cape region. They reside in silk-lined tunnels beneath rocks and logs.
The severity of envenomation by H. lightfooti is still matter of speculation. However, bites of megalomorph spiders have been reported to produce symptoms that include a burning pain experienced at the bite site. After a latent period of 2 hours, patients may vomit continuously and show marked signs of shock, collapse, and be unable walk. No discoloration or swelling is usually visible at the site of the bite. Latrodectus antivenom has shown some promise for treating bites of this species in mice.
Members of the genus Sicarius are medium-sized spiders with a body length up to 0.6 inches (15 mm), and the width across the legs is about 2 inches (50 mm). Most species are reddish-brown to yellow in color without any distinct patterns. They often camouflage themselves with sand particles wedged between body hairs in order to blend into the background of their specific habitat. These spiders are shy and secretive, but they will bite when accidentally contacted.
Figure 21. Six-eyed sand spider (Siciarius sp.), South Africa. Photo: Genevieve.
Figure 22. Six-eyed sand spider (Siciarius sp.), South Africa. Photo: Museums of Cape Town.
There are 22 known species in the genus Sicarius which are broadly distributed in Zimbabwe, South Africa, Central and South America, and the Galapagos Islands. They are arguably the most venomous group of spiders in southern Africa. Six-eyed sand spiders have a virulent cytotoxic poison capable of destroying tissue around the site of the bite and throughout the body, causing massive internal bleeding. Tissue damage from a bite can be extensive and severe, but bites to humans are not well documented. However, under experimental conditions, rabbits envenomated with Sicarius venom died within 4-6 hours and autopsies revealed extensive damage to subdermal tissue and skeletal muscle. Also, there was swelling of the liver and damage to heart and kidney tissues as well as blocked arteries in the lungs. The severity of the damage depended on the amount of venom delivered by the spider, the health of the patient, or if the patient has allergies, the age of the patient and the site of the bite. Small children and the elderly appear to be the most adversely affected. Some patients display symptoms of stress. No antivenom is available.
The various common names applied to these South African spiders include wandering
spider, lizard-eating spider and dwaalspinaekop. The most common species implicated in human bites is Palystes natalius of South Africa. This is the largest spider in the region and females reach up to 1.6 inches (40 mm) in length with the male being only slightly smaller than the female. They are the only spiders which might be confused with the baboon spiders (Family Theraphosidae), but they can be distinguished from baboon spiders in having the eyes arranged in two sets of four rather than clustered in single, small clump. Other distinguishing characteristics of P. natalius include having a brownish-gray colored body while the ventral surfaces of the legs are bright yellow with transverse black bands, and a reddish oral region. These free-living spiders are often found running on the walls of houses. Palystes natalius is medically important because its venom causes convulsions and death in guinea pigs under experimental conditions. However, some researchers have argued that the guinea pigs died from shock from being pierced by the spider’s large chelicerae, and not from the venom. In one human case, the bite from this species produced a burning pain at the site of the bite accompanied by slight swelling, which persisted for few days.
Figure 23. Wandering spider (Palystes natalius), South Africa. Photo: Museums of Cape Town.
The bite of white-tailed spider (Lampona cylindrata, Lampona murina) of Australia reportedly can cause a burning pain followed by swelling and itching. Whether or not there may be formation of necrotic lesions similar to those of the brown recluse is an area of active scientific debate, however. Although necrosis has been recorded for white-tailed spider bites, some suspect the necrosis actually stems from contamination of the bite wound with bacteria (Mycobacterium ulcerans) carried on the fangs of the spider. However, such necrosis is rarely reported. White-tailed spiders can grow to 0.8 inch (20 mm) in length, and they typically inhabit cool, outdoor locations such as under bark, rocks and leaf litter, and in houses. They are widely distributed in Australia and Tasmania.
Figure 24. White tail spider (Lampona cylindrata), Australia. Photo: source unknown.
More than 200 species of yellow sac spiders in the genus Cheiracanthium are distributed worldwide. Some of the known dangerous species of Cheiracanthium are shown in Appendix 1. These spiders are relatively small (0.4 inch or 10 mm, body length), and yellowish in color. Sac spiders construct sack-like, silken tubes in foliage or under bark or stones in which they hide. Although fairly reclusive in nature, sac spiders will occasionally enter houses and other structures. Yellow sac spiders are aggressive and will bite defensively. The clinical significance of these spiders is not well known, but they have been shown capable of causing a painful bite with associated necrosis and occasionally systemic effects. However, several species of Cheiracanthum have been implicated in human envenomations, and they reportedly are responsible for upwards of 90% of all dangerous spider bites in South Africa.
The number of species of yellow sac spiders which can inflict dangerous bites is not known, but because some species are considered dangerous, all sac spiders should be considered a potential threat. Many reported “brown recluse” bites outside the known range of Loxosceles reclusa in the United States may be due to envenomation by yellow sac spiders or perhaps other spiders. In the United States C. inclusum is native while C. mildei is introduced. Cheiracanthium mildei was first identified as a cause of necrotic arachnidism in 1970, when it was linked with skin lesions in the Boston, Massachusetts area where it is the most common spider found in houses. This species also is common in houses in New York City, and may well be the cause of "brown recluse” bites rumors mistakenly reported from that area. In the late 1970's and early 1980's C. mildei produced a significant number of bites in the Provo, Utah area. Similarly, C. inclusum is reportedly responsible for bites in Georgia and southwestern Canada. Bites by C. inclusum are probably far more common and widespread than reported, and it is likely that more reports will surface as yellow sac spiders become better known as clinically significant species.
Figure 25. Yellow sac spider (Cheiracanthium sp.). Photo: Darwin Vest.
Figure 26. Hobo spider (Cheiracanthium mildei). Photo: Jeff Barnes.
Figure 27. Hobo spider (Cheiracanthium mildei) showing the eyes. Photo: Peter DeVries.
The bites of yellow sac spiders are not life threatening, but they can result in substantial necrosis due to their cytotoxic venom. Bites are generally characterized as producing instant, intense stinging pain, similar to that of the sting of a wasp or hornet. Following the initial sting there may be localized redness, swelling and itching; and eventual formation of a necrotic lesion. Healing of the necrotic lesions typically is complete within eight weeks. Systemic effects are usually not severe, but may include chills, fever, headache, dizziness, nausea, loss of appetite, and sometimes shock. Treatment of the local lesion should follow the same protocols as outlined for the hobo and brown recluse spiders. Corticosteroid therapy may be beneficial when systemic effects are present.
Other spiders that have been implicated in arachnidism include Argiope spp. (garden spiders), of which representatives can be found worldwide, and Phidippus spp. (jumping spiders) found primarily in the Western Hemisphere. However, the responses to the necrotic envenomations from these species are generally mild, although victims may exhibit localized distress. Similarly, some species of Lycosa (wolf spiders) distributed in the Western Hemisphere have cyanotic venom that may produce localized necrosis. Most envenomations by wolf spiders involve intense pain and reddening at the bite site, with variable amounts of swelling. In some instances there is bleeding at the puncture sites because of the powerful jaws of these spiders. The bites of one South American species, Lycosa raptoria, have been shown to produce necrotic lesions, and victims may experience swollen lymph vessels around the bite area with eventual eschar formation and sloughing of the wound.
Figure 28. Garden spider (Argiope sp.), North America. Photo: Jeff Barnes.
Figure 29. Jumping spider (Phidippus sp.), Thailand. Photo: John Moore.
Figure 30. Wolf spider (Lycosa avida). Source uknown.
Other spiders from different regions of the world may also produce mild arachnidism, but such cases are seldom reported and are not generally considered medically significant. Treatment for these milder cases of necrosis should include immobilization and elevation of the bitten area, cold compresses, analgesics, tetanus boosters, and systemic antibiotics for secondary infections.
Though widely feared, tarantulas (Family Theraphosidae) are not particularly dangerous to people. Bites from their long, needle-like fangs, can be quite painful, and the setae shed from their bodies can be a painful urticarial irritant when introduced into the eyes or mucous membranes. However, their venom produces a reaction comparable in physical character to that of bees and wasps. Localized reactions for a tarantula bite can be treated with topical corticosteroids, systemic antihistamines, and cold compresses.
Figure 31. Tarantula. Photo: David Bowles & Mark Pomerinke.
Scorpions (Order Scorpiones) are a largely nocturnal, secretive group of animals widely distributed in tropical, subtropical, and desert habitats worldwide generally located south of 45oN latitude. Although all scorpions are venomous, only a few of the over 1000 known species are dangerous to humans. The stings of most species are similar to that of a bee or wasp. Most scorpions are not aggressive and stinging incidences usually occur only accidentally. However, scorpions stings remain a serious public health menace in many areas of the world. For example, approximately 200,000 people are stung by scorpions yearly in Mexico with 700-800 deaths. In Tunisia, data collected from 1986 to 1992 showed 30,000-45,000 cases per year of people stung by scorpions, and the number of deaths varied from 35 to 105 per year, largely among children. Some medically important scorpions and their geographic distributions are shown in Appendix 1.
Figure 32. Stinger of Parabuthtus granulatus. Photo: Museums of Cape Town.
Most potentially lethal scorpions belong to the Family Buthidae which primarily is distributed in Africa and Southeast Asia. However, all scorpion stings, regardless of geographic location should be treated as potentially dangerous unless the scorpion can be positively identified. For example, several species of Centruroides distributed from Mexico southward in the Americas have stings with serious medical consequences but other species in this genus only produce painful encounters. Among the most dangerous scorpions in the world are Centroides sufussus in Mexico, Tityus serrulatus in Brazil, and the infamous yellow scorpion of the Middle East, Leiurus quinquestriatus. Of the 86 species of scorpions known from India, only two species Mesobuthus tamulus, the common red scorpion, and Palamneits swammerdami, are potentially lethal. Indeed, the common red scorpion has killed many people with a historic mortality rate around 30%. In the western Cape of Africa, Parabuthus granulatus is the most important venomous species while Androctonus australis and Buthus occitanus in northern Africa are regularly implicated in stinging humans with serious consequences. Opistophthalmus glabrifrons, Family Scorpionidae, is widespread in southern Africa, and is able to produce a variety of dangerous systemic symptoms, but no deaths have yet been attributed to this species. Androctonus crassicauda and Buthus occitanus generally are considered to be the two most dangerous scorpions in Jordan. Similarly, A. crassicauda is the second most frequent source of scorpion sting in southwest Iran where it is considered to be a significant social hazard. This species is responsible for many deaths annually, mostly among children. Of 2,534 patients in one study in southwest Iran, three scorpion species accounted for nearly all of the stings, i.e., Androctonus crassicauda (41%) and Mesobuthus eupeus (45%) (Family Buthidae), and Hemiscorpion lepturus (13%) (Family Scorpionidae). In the United States, the only scorpion capable of inflicting a fatal sting is Centruroides exilicauda (=C. sculpturatus, C. gertschi) which is distributed in Arizona, California, Utah, and western Mexico. However, no deaths in the United States have been attributed to this species since 1968.
Figure 33. Androctonus crassicauda, Middle East. Photo: Al Sirhan.
Figure 34. Buthus occitanus, Middle East. Photo: Danne Rydgren.
Figure 35. Centruroides exilcauda, North America. Photo: Kelly Swift.
Figure 36. Hottentotta jayakari, Middle East. Photo: Eric Ythier.
Figure 37. Yellow scorpion, (Leiurus quinquestriatus), Middle East. Photo: W. Wüster.
Figure 38. Mesobuthus eupeus, Middle East. Photo: G. Witt.
Figure 39. Red scorpion (Mesobuthus tamulus), India. Photo: Eric Ythier.
Figure 40. Thick-clawed scorpion (Opisophthalmus glabifrons), South Africa. Photo: R. David Gabon.
Figure 41. Parabuthus transvaalicus, South Africa. Photo: Kelly Swift.
Figure 42. Tityus stigmurus. Photo: W. Wüster.
Most dangerously venomous scorpions have long and slender pedipalps (“claws”) in comparison to those of less venomous species which tend to have more robust pedipalps. This has led to the simple, although not universal, rule that scorpions with thin claws and thick tails tend to be more venomous than those with stout pedipalps and thinner tails. The toxicity of the venom is therefore associated with the ability of the scorpion to subdue prey with the pedipalps. In southern Africa, thick clawed scorpions belonging to the families Scorpionidae, Bothriuridae and Ischnuridae, and are generally assumed to be harmless. However, 0pistophtalmus glabrifrons is an exception to the rule. Opistophthalmus species are burrowing scorpions, and probably never leave their burrows except when coming out to mate. This probably accounts for the timing and relative rarity of their stings.
Figure 44. Euscorpius italicus, Europe. Photo: James Cokendolpher.
Figure 45. Giant hairy scorpion (Hadrurus arizonensis), North America. Photo: Liberty Haven Ranch.
The effects of scorpion venom on people are highly variable with severity ranging from localized, self-resolving pain to death. For all scorpion stings, every effort should be made to establish the species responsible because the relative seriousness of envenomation is species dependent and varies widely. Additionally, the response to scorpion envenomation may vary with the general health and age of the victim, their physiology and genetics, and emotional condition. Further variability may be attributed to the site and depth of sting penetration, quantity of the injected venom, and the proportion of the venom reaching the circulatory system. The severity of complications often seen in children likely is due to the higher concentration of venom per unit volume of blood. Although individual play a key role in determining the reaction of stinging victims, other factors also may be involved.
Scorpion venom contains both hemolytic and neurotoxic components of which the former produces the pain and swelling associated with stings. The local and systemic responses associated with envenomation often are quite different and variable. The venom of some species may produce severe swelling and discoloration at the site of the sting while that of other species causes pronounced swelling, inflammation and pain. Although the general initial response to a scorpion sting is immediate local burning pain, some species with potentially lethal venom often cause little initial pain and produce minimal or no swelling, inflammation, and discoloration. However, the sting site may become painful to the touch and have a "woody" feeling. Some patients develop dark blue skin patches usually surrounded by a red halo within the first hour following a sting. These areas may gradually become hardened and inflamed followed by necrosis and subsequent sloughing of the skin. Large blisters may develop around the sting site, and extensive ulceration may follow. In cases of severe envenomation, the hemolytic components of venom can destroy red blood cells, disrupt the blood ability of blood to clot, and other cardiovascular complications can occur. Onset of acute kidney failure following scorpion envenomation can result within 24 hours to a few days following the sting and is sometimes typified by the presence of blood in the urine, and associated anemia and jaundice from destroyed blood cells. Some patients may require kidney dialysis. Although most patients have difficulty producing urine, other patients may start secreting abnormal amounts of urine between 6 and 21 days after a sting.
The neurotoxic fraction of the venom, depending on the species involved, can produce a broad range of dangerous and potentially fatal reactions when present in sufficient quantity. This fraction of the venom contains a variety of polypeptides that interfere with ionic balance and channel activity in the nervous system. The primary and initial effects are on the peripheral nervous system which causes intense pain, altered heart activity, and numbness. Other symptoms associated with the neurotoxic component of the venom include muscle twitching, crying, salivation, profuse sweating, respiratory distress, urinary urgency, nausea, paresthesia of the tongue, restlessness, stiffness of the joints, convulsions, and increased muscle activity around the eyes. For the stings of some species, pain can be negligible initially, but patients may seek medical treatment hours to days later when they have already developed swelling and inflammation with gradually increasing local pain. Another common response in children is an extreme form of restlessness characterized by excessive neuromuscular activity (jerking and spasms). Typically, blood pressure, body temperature, and tendon reflexes often increase while motor skills become impaired. Other striking features include the inability to write or manipulate small objects, difficulty articulating speech, and varying degrees of loss of pharyngeal reflexes. Heightened sensitivity to touch, cold or heat, muscle pain and cramps also occur in many patients. Systemic symptoms and signs usually develop within 4 hours of the sting, and anaphylaxis and death from cardiac or respiratory failure can occur within 24 hours. However, despite the seriousness of such symptoms in victims, death from scorpion stings has become less common due to the availability of antivenom in some areas where highly venomous species occur. Recovery often is complicated by varying degrees of respiratory dysfunction which tend to be more serious in children.
Treatment of envenomation by scorpions
Scorpion stings should always be treated as a medical emergency that requires treatment as soon as possible, especially when young children are concerned. Victims of scorpion sting, particularly if known dangerous species are involved, should be closely observed for at least 24 hours. Children and other high-risk patients should be hospitalized. Treatments for scorpion envenomation may range from using only a cold compress or ice on the sting site to administration of antivenom. Local pain can safely be relieved with a local anesthetic (e.g., xylocain or ice pack), and physician prescribed medications such as barbiturates, diazepam and atropine can be used for cases involving neurological symptoms. However, some analgesics like morphine, demerol, codein or other morphine derivatives, or paraldehyde, valium and thorazine may increase the toxicity of venom as much as seven times and should be administered cautiously. Corticosteroids, adequate hydration, blood transfusion and diuretics may help in management of severe cases. All patients with symptoms and signs of systemic envenomation should receive antivenom if available. The success of antivenom therapy depends on the conditions of the antivenom application (dose, route and time of injection after envenomation, etc.) and/or on the quality of antivenom. Serotherapy is more efficient when given as soon as possible after envenomation and with adequate quantities of antivenom. Surgical excision of the sting site may prevent harmful or fatal consequences in some patients.
Because the range of severity of envenomation is so variable among scorpions, the relative threat for a particular region should be assessed prior to deployment to that location to determine the requirement for obtaining appropriate antivenoms.
Chiggers are larval mites belonging to the family Trombiculidae. They are obligate ectoparasites on mammalian host before molting to the nymph and adult stages. Adults and nymphs are free-living and eat small invertebrates and their eggs, and organic matter. The microscopic larval stage cannot be seen without magnification, but the bright red, eight-legged adult, or harvest mite, is readily visible with the unaided eye. Chiggers occur in overgrown brush or grassy areas, especially where small rodents are abundant. Females lay eggs on the ground in groups of several hundred, and the resulting clumps of larval mites that hatch from these eggs can result in severe infestations of their hosts. Chiggers produce one generation each year, and they are most abundant during late summer and early autumn.
Larval chiggers actively crawl to the tips of vegetation such as grasses and wait for a host to pass. Various rodents and other small mammals are the normal hosts of chiggers, but unwary humans become hosts when they venture into chigger habitat without personal protection. Once on the host, the larval chiggers move to an ideal feeding spot where they attach themselves tightly to the skin. Contrary to popular belief, chiggers do not burrow into the skin or suck blood. They pierce the skin (often around a hair follicle) to feed on lymph and dander and in the process they introduce digestive enzymes into the host tissues. The chiggers then begin to feed on the liquefied host tissues. Subsequently, and usually after the chigger has left the host, the sourronding tissues to become inflamed and each bite has a characteristic red welt with a white, hard central area. The rash and intense itching associated with chiggers therefore is an allergic reaction to the mite's salivary secretions. Secondary infections ma result from scratching the bite site. After becoming fully fed, the chigger drops from its host, goes into the ground and enters a quiescent stage. In the fall of the year, it becomes a bright red adult that overwinters in that stage.
Two genera of chigger mites, each containing many species, are of concern to deployed military forces. They are Eutrombicula and Leptotrombidium. Chiggers in the genus Eutrombicula do not transmit any known pathogens to people, but they can cause irritating bites, dermatitis and severe itching when they feed on the unsuspecting host. They are widely distributed in the Western Hemisphere, and Europe. By comparison chiggers in the genus Leptotrombidium are the vectors of scrub typhus throughout Asia and portions of Australia. The bite of Leptotrombidium often does not itch, or at least not as intensely, as those of Eutrombicula. Also, a black necrotic lesion known as an eschar develops where the chigger fed.
Figure 47. Chigger (Eutrombicula sp.), North America. Photo: Richard C. Russell.
Figure 48. Leptotrombidium deliense, Asia. Drawing: D. S. Kettle.
Figure 49. L. orientale, Asia. Photo: Tai Soon Yong.
Figure 50. L. scutellare, Asia. Photo: Infectious Diseases Surveillance Center, Japan.
Figure 51. Eschar at the site of a Leptotrombidium bite. Photo: Richard C. Russell.
Itching associated with chigger bites can be alleviated through use of over-the-counter topical corticosteroids and antihistamines. Hot showers/baths also will help reduce itching. In cases of severe dermatitis associated with chigger bites, a physician should be consulted for appropriate treatment options.
Scabies mites (Sarcoptes scabei) are obligate parasites of humans that feed on skin. All life stages, exclusive of the eggs, are parasitic. The mites are tiny (0.01 inch, or <0.4 mm), but they have a rapid life cycle of 14 days or less. Mites are spread from person to person through direct contact or exchange of infested clothing. Positive identification is done through skin scrapings and microscopic identification.
Figure 52. Scabies mite (Sarcoptes scabei). Illustration: D. S. Kettle.
Scabies mites produce two general types of lesions on the host including burrows and reddened rash-like lesions. The burrows can be either intact or excoriated (open to the surface) and are created by the female mite as she tunnels into human skin while laying eggs in the process. The intact burrows appear as distinct raised, linear, and reddened marks, and those that are excoriated can become secondarily infected resulting in the formation of pustules and encrustations. Although infestations on a person may be widespread most are found on the extremities such as hands, wrists, elbows, armpits, breasts, and genitalia. The reddened rash-like skin lesions are most commonly found on the trunk while the burrows may be more generally distributed on the patient. Secondary infections may result from scratching the bite site.
Patients infested with scabies can be successfully treated with any of a variety of prescribed topical chemical treatments that most commonly include permethrin as an active ingredient. However, itching may still occur for several weeks following successful treatments which can be minimized with use of topical corticosteroids and systemic antihistamines. Bed linens recently used by scabies patients should be washed in hot water to reduce the chance of reinfestation.
Other medically important mites that bite people
Several other types of mites are occasionally known to attack humans, but such attacks are relatively rare in comparison to chiggers and scabies mites. Unlike the chigger or scabies mites, these mites feed on the host’s blood, and the initial bites are usually painful. They include the chicken mite (Dermanyssus gallinae), spiny rat mite (Laelaps echidninus), house mouse mite (Liponyssides sanquineus), tropical rat mite (Ornithonyssus bacoti), tropical fowl mite (Ornithonyssus bursa), northern fowl mite (Ornithonyssus sylviarum), and straw itch mite (Pyemotes tritici). Their natural hosts include various rodents and birds. Exposure to these mites often is occupationally related and attacks are self-limiting when the victim is no longer exposed to the source of the mites. They do not attach to the host for long periods, but rather they only attach long enough to take a blood-meal.
Figure 54. Tropical fowl mite (Ornithonyssus bursa). Photo: Richard C. Russell.
Figure 55. Spiny rat mite (Laelaps echidnina). Drawing: Australia, CISRO.
Figure 56. Straw itch mite (Pyemotes tritici). Photo: USDA-ARS.
Figure 57. Straw itch mite bites. Photo: source unknown.
The house mouse mite is medically important because it is the vector of rickettsial pox (Rickettsia akari) in humans. It is distributed worldwide and it normally inhabits the nests of rodents. However, in the absence of rodents, or when rodent populations are very large, these mites will attack people. In habitats where rodents have been killed, the mites will leave their dead hosts, congregate around heat soures, such as hot pipes and stoves and seek alternative food sources, including people. Similarly, the tropical rat mite occasionally feeds on humans causing painful bites, but this species is not known to transmit any diseases to humans. This species has a much wider distribution than the tropics and it has also is known from temperate regions. The spiny rat mite commonly parasitizes Norway rats and roof rats. Although the spiny rat mite also will bite people in the absence of their natural hosts, this species is not a known vector of disease pathogens that can affect people.
Reactions from the bites of these various mites can be either localized or widespread depending on the number of bites inflicted. The resulting reactions are produced through a combination of allergic sensitization and toxins secreted by the mites during feeding. Skin lesions generally appear as a reddish papule with a central hemorrhagic area around the puncture wound, or occasionally a fluid-filled vesicle occurs. Often these lesions itch intensely, and become crusted and secondarily infected. Treatment typically includes use of topical corticosteroid and anti-pruritic (itching) ointments.
There are two common dust mites of concern to human health, the American house dust mite (Dermatophagoides farinae) and the European house dust mite (D. pteronyssinus). Both mites are likely distributed worldwide. Due to their microscopic size (<300 µm, or <0.01 inch in length) and translucent bodies, dust mites are not visible to the naked eye. They live in bedding materials, furniture, carpet, stuffed toys and old clothing.
Figure 58. European house dust mite (Dermatophagoides pteronyssinus). Illustration: D. S. Kettle.
Figure 59. American house dust mites (Dermatophagoides farinae). Photo: USDA.
Dust mites feed on the dead skin (dander) from the bodies of people and animals and other organic material. Some people experience allergic reactions from exposure to dust mites and their fecal pellets. Symptoms are usually respiratory in nature and include sneezing, itching, watery eyes, wheezing. Occasionally a red rash develops, especially around the neck. Other allergic reactions may include headaches, fatigue and depression. Some studies have suggested that dust mites may be a key factor in 50 to 80 % of asthma cases. The heaviest infestations of house mites typically occur in beds and a mattress that may serve as home to millions of mites. Carpeting and upholstery also can support large mite populations. Dust mites thrive in warm, moist surroundings where relative humidity is above 50%.
Because complete control of dust mites in houses is not possible, reducing their populations and associated allergins through source reduction and humidity control are the most practical management approaches. Effective control of mites requires maintenance of relative humidity below 50% which can be achieved with a dehumidifer. Use of HEPA filters on air conditioner or heater vents is not considered to be practical or necessary, and may actually aggravate mite problems because the small holes of the filters will force air out of vents at a higher velocity, stirring up more dust than if filters were not used. Chemical control is not necessary, nor will it have a lasting effect on dust mite populations. For people who are extremely sensitive to dust mites, several control measures, consisting primarily of sanitation, can be taken to reduce dust mite populations. Control measures may include frequently vacuuming carpets and other surfaces that collect dust and disposing of the dust bag immediately after use. Alternately, carpeting in homes can be removed and replaced with tile or wooden floors. Bedding materials, including pillow cases, sheets, blankets and mattress pads should be washed every other week in hot water (130 °F or 54 oC), or enclose mattresses, box springs and pillows in zippered allergen- and dust-proof covers. Eliminating or reducing fabric wall hangings such as tapestries or pennants, and covering or replacing upholstered furniture also is beneficial.
Grain or flour mites (Acarus siro) are important pests of a wide variety of grains and dried fruit and vegetables including human food and animal feed products. Flour or grain mites are tiny (<0.03 inch or 0.76 mm) pale, soft-bodied, pearly or grayish-white, with legs varying in color from pale yellow to reddish-brown. Each leg has one claw at the end. The males have enlarged forelegs which bear a thick spine on the bottom side. These two characters can be used to separate Acarus from other mite genera. Grain mites are widely distributed throughout temperate regions worldwide, and they are less common in tropical areas. These mites do not feed on people, but they are the cause of an itchy rash known as "grocer's itch" and related allergic reactions in sensitive individuals exposed to their setae and spines. Grain mites thrive under high moisture conditions and are often found in conjunction with fungal growth. Severe infestations by these mites can result in brownish tinge over grain products known as "mite dust". When the mites are crushed during handling, they give off a "minty" odor.
Figure 60. Grain mite (Acarus siro). Photo: source unknown.
Ticks are grouped into two families: the Ixodidae or hard ticks, and the Argasidae or soft ticks. Hard ticks are responsible for transmitting the majority of tickborne diseases to humans while soft ticks are the primary vector of relapsing fever. Some of the more common and medically important ticks and their general distributions are shown in Appendix 1. In addition to transmitting disease agents, certain hard ticks may cause tick paralysis in people and other animal hosts they feed on. Tick paralysis at onset involves leg weakness and dysfunction, but it eventually can progress to complete paralysis of the extremities and respiratory failure. Recovery is usually quick once the tick is removed. General reactions associated with tick bites can include swelling, erythema, parathesia, blistering, itching, discoloration and hardening of the skin, necrosis, and nodule formation usually resulting from the mouthparts remaining in the host following removal of the tick. Secondary infections and localized gangrene can occur if the bite wound is not disinfected. Although uncommon, systemic symptoms can include nausea, vomiting, diarrhea, irregular pulse, shortness of breath, fever, gastrointestinal irregularities, restlessness, muscular weakness, drooping eyelids, sensitivity to light, delirium, hallucinations, and generalized pain. However, many of these latter symptoms can overlap with those of various tick-borne disease and tick paralysis making it difficult to determine their true source. Another unusual condition associated with tick bites is tick-bite alopecia or the loss of hair around the bite wound with associated mild necrosis. This condition apparently stems from a reaction of the victim to toxins in the tick saliva. The patches of lost hair may be as large as 2 inches (50 mm) in diameter and scarring from the necrosis. Tick-bite alopecia is self-limiting and hair regrowth is usually complete within about two months, but scarring may be long-term.
Figure 62. Lone star tick (Amblyomma americanum). Photo: Mat Pound.
Figure 63. Bont tick (Amblyomma hebraeum). Photo: Mat Pound.
Figure 64. Rocky Mountain wood tick (Dermacentor andersoni). Photo: Mat Pound.
Figure 65. American dog tick (Derrmacentor variablis). Photo: Mat Pound.
Figure 66. Australian paralysis tick (Ixodes holocyclus), female. Photo: Stephen L. Doggett.
Figure 67. Australian paralysis tick (Ixodes holocyclus), male. Photo: Stephen L. Doggett.
Figure 68. Black-legged tick (Ixodes scapularis). Photo: Scott Bauer.
Figure 69. Brown dog tick (Rhipicephalus sanguineus): Photo: Mat Pound.
The best means of avoiding tick bites is situational awareness and avoidance. However, when ticks are found on the body they should be removed properly and as soon as possible. The longer a tick remains attached, the more engorged and difficult it becomes to remove, and the more likely it may transmit a disease agent. Ticks can also shed pathogens in their feces, and cuts or abrasions can become contaminated if handled with bare fingers. Pathogens in tick feces can also be introduced through the mucus membranes of the nose or eyes.
There are several inappropriate ways of removing attached ticks including covering them with vaseline, applying fingernail polish or similar chemicals, burning them off with fire or matches, and detaching them with various commercial “gadgets.” However, such methods may actually do more harm than good, generally do not work as intended, and therefore should not be used. The most appropriate method for removing an attached tick is to: 1) place the tips of medium-tipped forceps around the area where the mouthparts enter the skin; 2) with steady slow motion, pull the tick away from the skin or slide the removal device along the skin; 3) do not jerk, crush, squeeze or puncture the tick; 4) after removal, place the tick directly into a sealable container. Disinfect the area around the bite site using standard procedures. If possible, keep the tick alive for identification and pathogen testing. Place it in a labeled (date, patient), sealed bag or vial with a lightly moistened paper towel then store at refrigerator temperature. If forceps are unavailable and the fingers must be used to remove the tick, contamination of the skin can be avoided by using rubber gloves, plastic, or a paper towel.
Camel Spiders (Order Solifugae)
are more properly known as wind scorpions, sunscorpions, or sunspiders. They
are not spiders or scorpions, but a distinct arachnid group consisting of
several hundred species distributed in tropical and desert regions worldwide.
They are primarily nocturnal creatures that hide in animal burrows, and under
rocks and other objects. Although windscorpions lack venom glands, their
powerful jaws are capable of inflicting painful bites. Reports of camel spiders
chasing people, are simply a result of their seeking shade from the sun—as the
person moves to avoid the camel spider, it follows them in an effort to stay in
the shade thus giving the impression of being chased. Tales of their ferocity
and gargantuan sizes are greatly exaggerated. They do not attack or prey on
large mammals, and they feed on a variety of other invertebrates. Situational
awareness and avoidance are the keys to avoiding camel spiders.
Figure 71. Camel spider. Photo: Australian Air
Force.
Collembola, or springtails,
generally are free-living, primitive insects that feed on organic debris or
decaying matter. However, some species belonging to the families Isotomidae and
Entomobryidae have been found in skin scrapings of patients whose symptoms
originally were attributed to lice or scabies. In some instances, these
patients were initially thought to be suffering from delusory parasitosis.
Collembola are not considered to be parasitic and their association with human
skin may be due to its high moisture content and/or the association of dead
tissue, fungal infections, or pollen. Therefore, patients who complain
their “skin is crawling” may not be delusional and they should be referred to a
dermatologist for skin scrapings to rule out the occurrence of collembolans.
Figure 72. Examples of different types of
Collembola. Photo: John R. Meyer.
Lice in the families Pediclulidae and Pthiridae (Order Phthiraptera) are exclusive and obligate parasites of humans that are distributed worldwide wherever people live. Lice are wingless, variously colored (usually gray, brown or black), equipped with prominent tarsal claws, and they range in size from about 0.09-0.13 inch (2.5 to 3.5 mm). The eggs of lice, or nits, are cemented to hairs in the case of head a
