The phylum Arthropoda contains many parasitic species, including ticks and mites (class Arachnida, subclass Acari) and insects (class Insecta). Crustaceans that parasitize aquatic animals also belong to this phylum (see Chapter 6). Arthropods are characterized by jointed appendages in the adult, and sometimes immature, stages as well as the presence of exoskeletons. This chapter presents a selection of arthropods that are common or important in domestic animals; we are grateful to Dr. Ellis Greiner, University of Florida (retired), who provided the original text. Mites and ticks are divided into two parts: the gnathosoma, which bears the mouthparts (pedipalps, chelicerae), and the idiosoma, where the jointed appendages (legs) and reproductive structures are found. Upon larval emergence from the egg, mites and ticks develop through simple metamorphosis to subsequent nymphal and adult stages. Larvae of ticks and mites have six legs; nymphs and adults have eight legs. Nymphal ticks and mites usually closely resemble the adults but are smaller and lack a genital opening. The majority of parasitic mites are microscopic, rarely exceeding 1 mm in length. Female mites are usually larger than males. All stages are covered by a soft integument. Respiration may occur directly across the integument (astigmata) or through spiracular openings (stigmata) associated with tracheal ducts; stigmata are often used in identification. Scales, spines, or setae (hairs) on the body and claws or suckers on the legs (Fig. 5.1) are also used in identifying the organisms. Many common sarcoptiform (round‐bodied) mites resemble one another, but they can be differentiated on the basis of the characteristics outlined in Table 5.1. Fig. 5.1 Important characteristics for identification of a number of common mites are length and segmentation of the stalk (pedicle) connecting a terminal sucker to the leg. In Sarcoptes scabiei (A) the stalk is long and unjointed (arrow) whereas Psoroptes spp. mites have a long, jointed pedicle (B). Table 5.1. Microscopic characteristics of some mites important in veterinary medicine Most common mite infestations are diagnosed by deep or superficial skin scrapings. For a deep skin scraping, a dulled, rounded scalpel blade (#10) is coated with mineral oil. The site selected for scraping should be at the periphery of a lesion or the predilection site of the suspected parasite. The blade should be scraped back and forth over the skin until capillary bleeding is evident (a shallower scraping can be done for surface‐dwelling mites). For collection of Demodex, the follicle mite, a fold of skin should be gently compressed between the fingers to express the mites before scraping. The debris collected on the scalpel blade is then placed on a microscope slide, a coverslip applied, and the material examined using the 10× microscope objective. Several slides may need to be examined before mites are found, especially in cases of Sarcoptes infestation. To recover surface mites, such as Cheyletiella spp., a superficial scraping that does not cause bleeding is made with a scalpel blade coated in mineral oil. Alternatively, scurf can be combed from animals and examined directly, or clear tape can be used to collect material. The tape is pressed to the hair coat in an affected area and then placed on a microscope slide, trapping skin debris and mites against the slide and allowing microscopic examination. If mites are shipped to a veterinary diagnostic laboratory for identification, they should be stored in 70% alcohol. Storing skin scrapings and mites dry may prevent successful identification. PARASITE: Sarcoptes scabiei (Figs. 5.2–5.5) Common name:Itch mite or scabies mite. Taxonomy: Mite (family Sarcoptidae). Host: Host‐specific varieties of Sarcoptes scabiei are found on a wide range of hosts including dogs, pigs, humans, ruminants, horses, rodents, and camelids. Traditionally, each mite is referred to according to the host on which it was found (S. scabiei var canis, S. scabiei var suis, S. scabiei var hominis, etc.). Geographic Distribution: Worldwide. Location on Host: On dogs, the margins of the ear, lateral elbows, and lateral hocks are most commonly affected. In pigs, the ears, neck, and back are infested. Over time, large portions of the skin can be involved. Life Cycle: Transmission of Sarcoptes scabiei occurs following direct contact with an infested animal or fomites (e.g., clippers). Mites burrow deep into the epidermis, depositing eggs and feces. The life cycle from egg to adult requires approximately 3 weeks to complete. Laboratory Diagnosis: To confirm the diagnosis, examine multiple, deep skin scrapings from the margins of affected areas. When mites are not detected, patients may be treated presumptively and the diagnosis confirmed upon resolution of pruritus. Fecal examination is also useful in revealing mites and mite eggs ingested during grooming. In pigs, S. scabiei is found in hyperkeratotic crusts on the margins of the pinnae. On the farm, this crusted material can be removed and crumbled over dark paper to reveal the tiny, motile mites. Digesting crusts with 10% sodium hydroxide may also reveal mites. Size:Females approximately 400 μm; males approximately 250 μm Clinical Importance: Mange caused by Sarcoptes scabiei is extremely pruritic and often accompanied by alopecia, hyperkeratosis, and dermal thickening. In North America, infestations occur most commonly in dogs and pigs; mites from animals readily transfer to humans and cause self‐limiting pruritus. Fig. 5.2 Pruritic mite infestations may stimulate intense grooming by the host, resulting in the presence of both mites and eggs (not shown) in the feces. Fig. 5.3 Sarcoptes and related mites are typically round bodied. The third and fourth pairs of legs (arrows) are short and often do not project beyond the margin of the body. Photo courtesy of Dr. Heather Walden, College of Veterinary Medicine, University of Florida, Gainesville, FL. Fig. 5.4 Sarcoptes scabiei var canis causes “scabies” or “sarcoptic mange” in dogs. Lesions commonly occur on the face and along the margin of the ear as well as on the lateral elbows and hocks of infested dogs. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. Fig. 5.5 Sarcoptic mange in an alpaca. In chronic sarcoptic mange, affected skin is hairless, thickened, and wrinkled. These nonspecific changes also occur in other chronic skin diseases. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. PARASITE: Notoedres spp. (Fig. 5.6) Common name:Feline mange mite, Ear mange mite (rodents). Taxonomy: Mite (family Sarcoptidae). Host: Notoedres cati occurs on cats. Other species occur on bats, rodents, and other small mammals. Geographic Distribution: Worldwide. Location on Host: The head is usually infested first, but mites may spread to other regions of the body. Life Cycle: Similar to Sarcoptes scabiei. Laboratory Diagnosis: Mites are observed in deep skin scrapings. Size:Notoedres cati approximately 200–225 μm Clinical Importance: Feline notoedric mange is usually confined to the head and neck. Infestations are rarely seen in North America. PARASITE: Knemidokoptes spp. (Figs. 5.7 and 5.8) Common name:Scaly leg or scaly face mite. Taxonomy: Mite (family Knemidokoptidae). Host: Birds, including domestic poultry and pet birds. Geographic Distribution: Worldwide. Location on Host: Nonfeathered portions of the body, including feet, legs, and face. Life Cycle: Like Sarcoptes scabiei, transmission occurs by direct contact with infested birds or fomites, and all stages of the mite are found on the host. Laboratory Diagnosis: Mites can be found in skin scrapings collected from the periphery of lesions. Typically, the exudative lesions produced by the mites contain numerous small holes, giving them a honeycombed appearance. Size:Approximately 400 μm Clinical Importance: Knemidokoptes species burrow under the scales on the legs or nonfeathered portions of the face, inducing a serous exudate that hardens into crusts. These proliferative lesions eventually may cause trauma and disfigurement leading to the death of the host. Fig. 5.6 Notoedres mites are similar in appearance to Sarcoptes. However, the anus of Notoedres is located on the dorsal surface rather than the ventral. Notoedres also has scalloped scales on the dorsum rather than the sawtooth scales on Sarcoptes. The suckers on the front legs of both Notoedres and Sarcoptes are attached to the legs by long, unjointed stalks. Fig. 5.7 Knemidokoptes is a round‐bodied mite, generally similar in appearance to sarcoptiform mites. Fig. 5.8 Budgerigar with a deformed beak resulting from the proliferative lesion produced by Knemidokoptes infestation. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. PARASITE: Trixacarus spp. (Fig. 5.9) Taxonomy: Mite (family Sarcoptidae). Host: Guinea pigs (Trixacarus caviae) and rats (T. diversus). Geographic Distribution: Europe and North America. Location on Host: Lesions begin on the head, neck, and back but can spread to other areas. Life Cycle: Similar to Sarcoptes scabiei. Mites are readily transferred from the dam to young animals in the neonatal period. Laboratory Diagnosis: Mites are identified in skin scrapings. Size:Approximately 200 μm Clinical Importance: Trixacarus is the sarcoptic mange mite of guinea pigs. Infestation is associated with pruritus, alopecia, and hyperkeratosis and can become a serious problem in guinea pig colonies. Humans in contact with infested guinea pigs may develop transient lesions. PARASITE: Chorioptes bovis (Figs. 5.10 and 5.11) Common name:Foot mange, leg mange, itchy heel. Taxonomy: Mite (family Psoroptidae). Host: Varieties of C. bovis are found on ruminants, horses, and rabbits. Geographic Distribution: Worldwide. Location on Host: Chorioptes are found primarily on the lower body of the host. In horses, the mites are seen more often in breeds with feathered legs. In cattle, the rear legs, base of the tail, and back of the udder are most often affected. Life Cycle: Transmission is by direct contact or fomites. Chorioptes mites spend their entire life cycle on the skin surface. The life cycle can be completed in about 3 weeks. Laboratory Diagnosis: Mites are observed in skin scrapings. Chorioptes has short, unsegmented stalks bearing the suckers on the legs (Table 5.1). Size:Approximately 400 μm Clinical Importance: Infestation may be asymptomatic or cause only mild lesions in some animals. As mite populations increase, pruritus, alopecia, and crusting may develop. Fig. 5.9 Like other sarcoptiform mites, Trixacarus is a round‐bodied mite with short legs. Trixacarus caviae causes mange in guinea pigs. Fig. 5.10 Chorioptes mites are more elongated, with longer legs than the sarcoptiform mites. Suckers are evident on short, unsegmented stalks (arrows) at the end of the legs. Photo courtesy of Dr. Yoko Nagamori, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK. Fig. 5.11 Female Chorioptes mites with eggs present (arrows). Mite eggs are large, ~200 μm long, and may be seen retained within mites or found on fecal flotation from infested animals. Photo courtesy of Dr. Yoko Nagamori, Oklahoma State University, Stillwater, OK. PARASITE: Psoroptes spp. (Figs. 5.12–5.15) Common name:Scab mite (ruminants). Taxonomy: Mite (family Psoroptidae). Host: Psoroptes ovis is the cause of psoroptic mange in ruminants; P. ovis cuniculi (formerly referred to as P. cuniculi) is found on rabbits and ruminants. Psoroptes spp. can also be found on horses and some wildlife hosts. Geographic Distribution: Worldwide. Location on Host: Psoroptes ovis cuniculi is found in the ears of rabbits, sheep, goats, and horses. Other Psoroptes infestations are often first detected on the dorsum of the host but may spread to other areas. Life Cycle: Transmission is by direct contact or fomites. Unlike sarcoptiform mites, Psoroptes spp. do not burrow, and all stages are found on the skin surface. The life cycle can be completed in as little as 10 days. Mites may survive for several days off the host. Laboratory Diagnosis: Superficial skin scrapings should be collected from the periphery of skin lesions. Alternatively, skin scabs can be broken apart or digested and the residue examined microscopically. Crusts from the ears can be treated similarly when infestations of P. ovis cuniculi are suspected. Psoroptic mites are more oval in shape and have longer legs than sarcoptiform mites. Size:Approximately 750 μm Clinical Importance: Psoroptes is a highly contagious, economically important cause of skin disease in ruminants worldwide. Infestation leads to exudative dermatitis and hair loss. In the United States, the strain of P. ovis affecting sheep has been eradicated, and the bovine strain has diminished in importance since the introduction of macrocyclic lactone endectocide drugs. In severe cases, P. ovis cuniculi lesions on rabbits may extend beyond the ears to the face, neck, and back. Fig. 5.12 Psoroptic mange or “scab” can be a serious infestation in ruminants. In sheep, mite activity causes an exudate that forms a crust on the surface of the skin, with the resulting loss of the fleece over affected areas. Fig. 5.13 Psoroptic ear mange in a rabbit. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. Fig. 5.14 Psoroptes sp. mites have a more oval shape and longer legs than round‐bodied, sarcoptiform mites. This morphology is sometimes referred to as “psoroptiform.” Terminal suckers are connected to the legs by long, segmented stalks (arrow). Photo courtesy of Dr. Manigandan Lejeune, Animal Health Diagnostic Center, Cornell University, Ithaca, NY. Fig. 5.15 Psoroptes may be up to 800 μm in length. Shown here are specimens of Psoroptes cuniculi from rabbit ears. Figures 5.1B and 5.14 show a closer view of the jointed pedicle on some of the legs of Psoroptes. Photo courtesy of Dr. David Baker, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA. PARASITE: Otodectes cynotis (Figs. 5.16–5.19) Common name:Ear mite. Taxonomy: Mite (family Psoroptidae). Host: Dogs, cats, and ferrets. Geographic Distribution: Worldwide. Location on Host: Ear canal. Life Cycle: Mites complete their life cycle in the ear. Transmission occurs by direct contact or fomites. Kittens and puppies are easily infested by contact with the dam. Laboratory Diagnosis: Routinely diagnosed by otoscope or microscopic examination of aural exudate collected with cotton swabs. Size:Approximately 300 μm Clinical Importance: These mites are a common cause of otitis externa. Bacterial decomposition of otic secretions and exudate leads to the formation of black, waxy cerumen. Infested animals often suffer severe pruritus that may lead to self‐inflicted trauma. Heavy infestations may spread outside the ear to the face, neck, and back. Fig. 5.16 Otodectes cynotis infestation in a cat. The mites cause the production of black, waxy exudate in the ear canal. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. Fig. 5.17 Mating Otodectes cynotis mites from a ferret. Otodectes is another psoroptiform mite with an oval‐shaped body and long legs. They are similar in size and appearance to Chorioptes. In heavy infestations, it is common to find copulating mites in ear swab preparations. The short unsegmented stalks carrying the suckers can be seen in this photo. Fig. 5.18 Gravid female of Otodectes cynotis with egg present (arrow). Photo courtesy of Dr. Heather Walden, College of Veterinary Medicine, University of Florida, Gainesville, FL. Fig. 5.19 Male Otodectes cynotis. The pair of distinct circular structures evident on the posterior end (arrows) are copulatory suckers. Photo courtesy of Dr. Manigandan Lejeune, Animal Health Diagnostic Center, Cornell University, Ithaca, NY. PARASITE: Demodex spp. (Figs. 5.20–5.23) Common name:Follicle mite, red mange. Taxonomy: Mite (family Demodicidae). Host: Species of Demodex are host‐specific and have been identified from many animals, including dogs, cats, pigs, horses, cattle, goats, sheep, laboratory animals, and humans. Geographic Distribution: Worldwide. Location on Host: Sebaceous glands and hair follicles. Life Cycle: Mites are usually transferred from the dam to offspring in the neonatal period. All stages of the life cycle are found on the host. Laboratory Diagnosis: Deep skin scrapings are required for diagnosis. Compressing a skin fold before scraping aids in expressing mites from follicles and sebaceous glands. A high proportion of eggs and immature mites on skin scraping is considered indicative of a more severe infestation. Demodex mites and eggs are often ingested during grooming and identified by fecal flotation. Size:100–400 μm, depending on species Clinical Importance: Most animals harbor mites but do not develop clinical disease. When the immune system fails to keep mite populations in check, proliferation can occur leading to folliculitis, furunculosis, and secondary bacterial infection. Disease is seen most often in dogs and may be localized and self‐limiting or generalized, severe, and potentially fatal. Fig. 5.20 Demodex is most often seen as a clinical problem in dogs. Lesions often appear first on the face or forelegs. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. Fig. 5.21 In goats and cattle, clinical demodecosis is usually associated with the formation of nodular pustules. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA, and Dr. C. Williams, Langley, WA. Fig. 5.22 Demodex spp. mites (A) have a distinct, elongated appearance and are often described as looking like cigars with legs. Demodex canis reaches a length of ~390 μm. Eggs (B) are spindle‐shaped (~100 µm). Both may be present on skin scrape or found on fecal flotation from infested animals after self‐grooming. Photo courtesy of Dr. Manigandan Lejeune, Animal Health Diagnostic Center, Cornell University, Ithaca, NY. Fig. 5.23 Many animals are parasitized by Demodex spp. Shown here is Demodex from a gerbil. Hosts rarely show clinical signs of infestation. Photo courtesy of Dr. David Baker, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA. PARASITE: Cheyletiella spp. (Figs. 5.24 and 5.25) Common name:Walking dandruff. Taxonomy: Mite (family Cheyletiellidae). Host: Cheyletiella parasitovorax, C. yasguri, and C. blakei are seen on rabbits, dogs, and cats, respectively. Geographic Distribution: Worldwide. Location on Host: Cheyletiella infestations are usually seen on the back. In cats, the head is also often affected. Life Cycle: Transmission is by direct contact or fomites. Cheyletiella can be carried from one animal to another by fleas (Ctenocephalides). Mites can live up to 10 days in the environment. Laboratory Diagnosis: Cheyletiella is a fur mite and not a skin dweller, so only superficial skin scrapings are required for diagnosis. Alternatively, if material combed from the hair is examined against a dark background, mites can be seen as moving white dots (“walking dandruff”). The distinctive feature of the mite is the large palpal claws. Size:Approximately 400 μm Clinical Importance: Many infested animals do not show clinical signs. Young animals are most likely to show evidence of infestation, including crusting, increased skin scurf, and pruritus. In heavy infestations, hair loss may occur. Owners may develop lesions in areas of close contact with their animals. PARASITE: Psorobia (Psoregates) spp. (Fig. 5.26) Taxonomy: Mite (family Cheyletiellidae). Host: Mice (Psorobia simplex); related species (e.g. Psoregates spp.) are found on ruminants. Geographic Distribution: Psorobia simplex is found on mice worldwide. Psoregates ovis of sheep is uncommon and occurs in Australia, New Zealand, South Africa, and South America. Psoregates bos of cattle is also uncommon but has been reported from Africa, Australia, Europe, and North America. Location on Host: Psorobia simplex can be found anywhere on the body although lesions often develop in the ears and mite numbers are highest on the head and neck. Lesions of Psoregates ovis develop on the neck and shoulders and then spread to the flanks and rump. Cattle with Psoregates bos develop lesions on the dorsal head, neck, shoulders, rump, and back. Life Cycle: Similar to Sarcoptes scabiei. Mites readily move between animals in close contact. Laboratory Diagnosis: Mites are identified in skin scrapings. Size:100–200 μm; smaller than Sarcoptes scabiei Clinical Importance: Psorobia simplex can cause ear mange as well as small, white, dermal nodules in mice. Psoregates ovis causes fleece damage in sheep; Merinos are particularly susceptible. Cattle with psorergatic mange present with pruritus, scaling, and alopecia. Fig. 5.24 Cheyletiella is a surface mite that can be collected by brushing the hair coat or collecting material with sticky tape. In heavy infestations, mites may be found throughout the hair coat. Photo courtesy of Dr. Yoko Nagamori, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK. Fig. 5.25 Cheyletiella spp. are readily identified microscopically by the presence of large palpal claws (arrow). Small combs are present on the legs instead of the suckers seen in some other species of parasitic mites. Photo courtesy of Dr. Yoko Nagamori, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK. Fig. 5.26 Psorobia simplex from a mouse. Note the rounded body, short legs, and presence of small claws or combs rather than suckers on the end of each leg. Photo courtesy of Dr. Yoko Nagamori, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK. PARASITE: Lynxacarus radovskyi (Fig. 5.27) Taxonomy: Mite (family Listrophoridae). Host: Cats; other species infest bobcats and weasels. Geographic Distribution: Australia, southern United States, Caribbean, and Hawaii. Location on Host: Mites clasp the hairs of cats, primarily on the tail head, tail tip, and in the perineal area. Life Cycle: The entire life cycle is spent on the host. Infestation is by direct contact. Laboratory Diagnosis: Laterally flattened mites can be seen clinging to cat hairs. Eggs are attached to the hairs. Size:Approximately 450 μm Clinical Importance: Heavy mite infestations can affect the entire body and lead to poor condition of the hair coat. This mite is rare in North America. PARASITE: Leporacarus (= Listrophorus) gibbus (Figs. 5.28 and 5.29) Common name:Fur mite. Taxonomy: Mite (family Listrophoridae). This mite formerly belonged to the genus Listrophorus. Host: Rabbits. Geographic Distribution: Worldwide. Location on Host: Throughout the fur. Life Cycle: Transmission is by direct contact. All stages of the life cycle are found on the host. Laboratory Diagnosis: Mites are large enough to be seen as small specks on the hairs and can be collected by combing and examining hairs with a magnifying glass or microscope. Size:Approximately 350–500 μm Clinical Importance: Mites usually cause no clinical signs even though large numbers may be present. Fig. 5.27 The body of the Lynxacarus mite is laterally compressed like that of a flea and has large sternal plates that are used, along with the first two pairs of legs, to encircle the hair. Fig. 5.28 Male Leporacarus mites have a brown anterior shield that projects beyond the mouthparts. Males also have distinctive adanal clasping organs. Fig. 5.29 Adult Leporacarus on the hair of a rabbit. The female mites also bear an anterior shield. Photo courtesy of Dr. Yoko Nagamori, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK. PARASITE: Chirodiscoides caviae (Fig. 5.30) Common name:Fur mite. Taxonomy: Mite (family Listrophoridae). Host: Guinea pigs. Geographic Distribution: Worldwide. Location on Host: Attached to hairs. Life Cycle: Transmission is by direct contact with an infested individual or fomite. Laboratory Diagnosis: Mites are detected by examining hairs from the host. Size:Approximately 350–500 μm Clinical Importance: This mite is considered generally nonpathogenic. PARASITE: Mycoptes musculinus, Myobia musculi, Radfordia spp. (Figs. 5.31 and 5.32) Common name:Fur mite. Taxonomy: Mites (families Listrophoridae and Myobidae). Host: Mice and rats. Geographic Distribution: Worldwide. Location on Host: Hair coat. Life Cycle: Transmission is by direct contact; all stages of the life cycle are found on the host. Laboratory Diagnosis: Diagnosis is made by detecting mites on host hairs. Clinical Importance: Some infested animals tolerate large numbers of mites without clinical signs, although pruritus, erythema, hair loss, and thickened skin may occur in others. Secondary bacterial infections may develop. Fig. 5.30 Chirodiscoides from a guinea pig. The first two pairs of legs are adapted for wrapping around the hair shafts of the host. Photo courtesy of Dr. David Baker, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA. Fig. 5.31 Mycoptes musculinus from the hair coat of a mouse. In males, the fourth pair of legs is enlarged and directed backward. Photo courtesy of Dr. David Baker, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA. Fig. 5.32 Radfordia is found at the base of the hairs. The first pair of legs is modified for feeding and project forward. Radfordia is similar in appearance to another rodent fur mite, Myobia musculi. However, Radfordia has two claws on the second pair of legs, while Myobia has only one claw. PARASITE:Avian Feather Mites (Figs. 5.33 and 5.34) Taxonomy: Mites (numerous families and species). Host: Domestic and wild birds. Geographic Distribution: Worldwide. Location on Host: Species specialized for different feather environments. Life Cycle: Most mites live on the feather surface and feed on secretions and skin and feather debris. Quill mites live in the base of the feathers and feed on host tissue or fluids. Laboratory Diagnosis: Diagnosis is made by detection and identification of mites on feathers. Size:Variable with species Clinical Importance: Most feather mite infestations appear to cause little damage and are usually considered of minor clinical importance. Occasionally irritation, dermatitis, and feather damage develop. Fig. 5.33 Feather mite from a chicken. Feather mite species show great variation in morphology as a result of specialization for life in different parts of the avian feather environment. Photo courtesy of Dr. Manigandan Lejeune, Animal Health Diagnostic Center, Cornell University, Ithaca, NY. Fig. 5.34 Megninia, a feather mite from a finch. Feather mites infest various species of birds, often feeding at the base of feathers. Photo courtesy of Dr. Manigandan Lejeune, Animal Health Diagnostic Center, Cornell University, Ithaca, NY. PARASITE: Ornithonyssus sylviarum, O. bursa (Figs. 5.35 and 5.36) Common name:Northern fowl mite, tropical fowl mite. Taxonomy: Mite (order Mesostigmata). Geographic Distribution: The northern fowl mite, O. sylviarum, is found in temperate regions worldwide. The tropical fowl mite, O. bursa, is found in tropical and subtropical climates. Both species are found in the United States. Location on Host: Mites and egg masses can be found on the skin among the feathers. In poultry, O. sylviarum often concentrates around the vent, causing a dark discoloration of the area. Life Cycle: Ornithonyssus sylviarum spends its life on the avian host, whereas O. bursa spends greater periods of time off the host. Wild birds can introduce the mites into poultry facilities. Under appropriate conditions, the life cycle of O. sylviarum can be completed in a week. Laboratory Diagnosis: Large, grossly visible mites are observed on birds or in the environment. Size:Approximately 750 μm Clinical Importance: Scabbed, matted feathers develop on infested birds. In severe cases, anemia, production loss, and death may occur. Mites can act as vectors of other avian disease agents, including those causing Newcastle disease and fowl pox. Humans in contact with mites may also develop lesions. PARASITE: Ornithonyssus bacoti (Figs. 5.35 and 5.36), other Ornithonyssus spp. Common name:Tropical rat mite. Taxonomy: Mite (order Mesostigmata). Host: Rodents, wild birds; occasionally other animals and humans. Geographic Distribution: Worldwide. Location on Host: Skin. Life Cycle: Adult mites lay eggs in the environment. Mites visit the host only to feed; they spend the rest of the time in the host’s bedding or nest. The life cycle can be completed in about 2 weeks. Laboratory Diagnosis: Large, grossly visible mites are observed on animals or in the environment. Size:Approximately 750 μm Clinical Importance: In large numbers, this blood‐feeding mite can cause anemia, debilitation, and death. Humans in contact with infested laboratory or pet rodents may develop lesions. Lesions can also develop on pets and people when rodent or bird nests associated with human dwellings are abandoned, leaving mites behind to seek other hosts. Fig. 5.35 Ornithonyssus spp. belong to the mesostigmatid order of mites. These mites are quite large and have long legs in the anterior portion of the body. In Ornithonyssus spp., the anus (arrow) is at the anterior end of the anal plate. The anus of Dermanyssus spp., a morphologically similar mite, is located in the posterior portion of the anal plate. Photo courtesy of Dr. David Baker, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA. Fig. 5.36 Another characteristic used to differentiate Ornithonyssus from the similar genus Dermanyssus is the chelicerae (arrow). The chelicerae in this Ornithonyssus mite are shorter than the long, whip‐like chelicerae of Dermanyssus. PARASITE: Dermanyssus gallinae (Fig. 5.37) Common name:Red poultry mite. Taxonomy: Mite (order Mesostigmata). Host: Wild and domestic birds. Geographic Distribution: Worldwide. Location on Host: Mites can occur anywhere on the body. Life Cycle: Mites visit the host at night only to take blood meals. During the day, the mites are found in crevices in the environment. The life cycle can be completed in as little as 10 days. Adults can survive in the environment for several months without feeding. Laboratory Diagnosis: Mite infestation may be difficult to diagnose because the mites are not on the host during the day. Close examination of the environment may reveal mites under crusts of manure on perches or in nest boxes. If infestation is suspected in caged birds, the cage can be covered with a white cloth at night. In the morning, mites will be seen as small black or dark red dots clinging to the cloth. Size:Approximately 750 μm Clinical Importance: Heavy infestation can cause anemia and death, particularly in hatchlings. Hens may be reluctant to sit on their nests. Other animals and humans in close proximity to infested birds or their nests may also develop lesions. PARASITE: Pneumonyssoides caninum (Fig. 5.38) Common name:Nasal mite. Taxonomy: Mite (order Mesostigmata). Host: Dogs. A similar mite, Pneumonyssus simicola, is found in the lungs of rhesus macaques. Geographic Distribution: Worldwide. Location on Host: Nasal sinuses of dogs. Life Cycle: The life cycle of this mite is poorly understood, but transmission is thought to be by direct contact since mites are sometimes seen crawling on the nose. Laboratory Diagnosis: Large mites grossly visible in the nasal sinuses and passages or crawling outside the nostrils. Size:Approximately 1 mm Clinical Importance: Infestations are usually asymptomatic but may produce sneezing, rhinitis, sinusitis, and malaise. In captive rhesus macaques, Pneumonyssus simicola can cause significant respiratory disease. Fig. 5.37 Dermanyssus gallinae infests both domestic and wild birds. The anus of this mite is present in a more posterior position on the anal plate than in Ornithonyssus. Dermanyssus also has long, whip‐like chelicerae (not visible in this figure). Differentiating the genera may be helpful in determining appropriate control measures because of differences in life cycles. Fig. 5.38 Pneumonyssoides caninum, the nasal mite of dogs. A related mite, Pneumonyssus simicola, is the lung mite of several species of African monkeys. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. PARASITE: Ophionyssus natricis (Figs. 5.39 and 5.40) Common name:Snake mite. Taxonomy: Mite (order Mesostigmata). Geographic Distribution: Worldwide on captive snakes. Location on Host: Mites are found on the skin or under the scales of snakes and may also infest lizards. Life Cycle: Ophionyssus nymphs and adults feed and females deposit eggs in the environment after taking a blood meal. Larvae do not feed. The entire life cycle takes about 13–19 days. Infestation occurs by direct contact with an infested snake or its environment. Laboratory Diagnosis: Identification of large mites collected from snakes. Females that have taken a blood meal are dark colored. A cotton‐tipped swab can be dipped in mineral oil and used to collect mites for identification. Size:Females 0.6–1.3 mm Clinical Importance: Ophionyssus infestations are common in captive snakes. Affected animals may show irritation and depression. Shedding may increase, and snakes may soak themselves more frequently in water. Fig. 5.39 Ophionyssus mites are the most common external parasite on captive snakes and may seriously affect the health of the host. Female mites lay eggs off the host, and successful control of infestation requires environmental treatment. Photo courtesy of Dr. Yoko Nagamori, College of Veterinary Medicine, Oklahoma State University, Stillwater, OK. Fig. 5.40 Ophionyssus, like other mesostigmatid mites, has claws on the tips of the legs instead of the suckers seen in many other parasitic mites (Fig. 5.1). PARASITE: Trombiculid Mites (Figs. 5.41–5.43) Common name:Chigger, harvest mite, scrub itch mite. Taxonomy: Mites (family Trombiculidae). Host: Wide variety of animals and humans. Geographic Distribution: Several species parasitize a variety of hosts, including Eutrombicula alfreddugesi, E. splendens (North America), and Neotrombicula autumnalis (Europe). Location on Host: Predilection sites include the face, head, and legs. Life Cycle: Only the larval stage of chigger mites is parasitic. Eggs are laid in the environment. Larvae attach to a host and feed for 3–5 days and then complete development in the environment. Contrary to a commonly held misunderstanding, chiggers do not burrow beneath the skin. Adults are free‐living predators of other arthropods. Laboratory Diagnosis: Small, often orange or red mites are often seen in clusters on the face of the host. The presence of only larval stages is helpful in diagnosing chigger infestations. Size:Approximately 200–500 μm, depending on species Clinical Importance: Chigger mites cause intense pruritus. The feeding tube, or stylostome, left behind after mites are dislodged by scratching or detach to complete their development in the environment, is intensely irritating. Humans are also commonly infested by chiggers, with pruritic lesions frequently appearing in areas where clothing is constrictive (e.g., at the waistband of pants or top of socks). Fig. 5.41 Only the six‐legged larvae of chiggers are parasitic, which is helpful in identification of the parasites. This Blankaartia sp. chigger was removed from a bird. Fig. 5.42 Specimen of trombiculid larvae that cause mammalian chigger infestation. Photo courtesy of Dr. Jeffrey F. Williams, Vanson HaloSource, Inc., Redmond, WA. Fig. 5.43 Typical chigger lesions on the leg of a parasitologist. Chiggers may also cause pruritus and irritation on animals. Ticks are usually larger than mites, ranging in length from 3 to 12 mm, or more in the case of engorged females. Ticks are divided into two families: Ixodidae (hard ticks) and Argasidae (soft ticks). The Ixodid (hard) ticks are of greatest importance in veterinary medicine. Various hard tick species are vectors of a number of viral, bacterial, protozoal, and nematodal animal and human pathogens. In addition, hard tick species cause tick paralysis and tick toxicosis. All ticks pass from the egg through larval and nymphal stages before becoming adults and utilize one or more host animals during the developmental cycle. Eggs are always laid in the environment. Hard tick larvae are acquired by the host from the environment. All hard ticks undergo a single molt from the larval to the nymphal stage and a second molt from the nymph to the adult. These molts follow attachment and blood‐feeding on the host that usually lasts for several days. Tick species that remain on the host during the two molting periods are known as one‐host ticks. In two‐host tick species, the molt to the nymphal stage occurs on the host, but the engorged nymph leaves the host, molts in the environment, and then finds a new host. In the three‐host tick life cycle, both the larva and nymph leave the host to molt, attaching to a host again after each molt. In some cases, each tick stage prefers the same host species; in others, host preference may vary with the stage of the tick. In much of North America, the most important tick species are three‐host ticks. Soft tick life cycles are more variable than those of the hard ticks. Many soft tick species live in the environment and visit the host only briefly to take repeated blood meals. All stages of ticks are large enough to be grossly visible on animals, although larvae may be only a few millimeters in length and soft ticks usually do not attach for long periods. Hard ticks may attach anywhere on their hosts but are likely to be found attached in areas on the host that cannot be easily groomed, for example, the head, neck, and ears of most host species (Fig. 5.44), and also the tail of horses. Because ticks are important vectors of pathogens that may result in disease (e.g., Lyme disease, Rocky Mountain spotted fever, ehrlichiosis, cytauxzoonosis, anaplasmosis, etc.), they should be removed as quickly as possible using forceps or tweezers instead of fingers to reduce the possibility of contact with tick body fluids containing infectious organisms. The tick should be firmly grasped directly behind the point of attachment to the skin and then pulled off. Often a small portion of skin will also be pulled away.
CHAPTER 5
Diagnosis of Arthropod Parasites
SUBCLASS ACARI (MITES AND TICKS)
Mite Identification
Genus
Leg characteristics
Egg‐laying female
Male
Anus
Sarcoptes
Suckers on long, unsegmented stalks on legs 1, 2; many pointed scales on dorsum
Suckers on long unsegmented stalks on legs 1, 2, 4; few pointed scales on dorsum
Terminal
Notoedres
Suckers as above; many prominent rounded scales on dorsum
Suckers as above; few rounded scales on dorsum
Dorsal
Knemidokoptes
No suckers
Suckers on unsegmented stalks on legs 1, 2, 3, 4
Terminal
Psoroptes
Suckers on long, segmented stalks on legs 1, 2, 4
Suckers on long, segmented stalks on legs 1, 2, 3
Terminal
Chorioptes
Suckers on short, unsegmented stalks on legs 1, 2, 4
Suckers on short, unsegmented stalks on legs 1, 2, 3, 4; legs 4 rudimentary
Terminal
Otodectes
Suckers on short, unsegmented stalks on legs 1, 2; legs 4 rudimentary
Suckers on short, unsegmented stalks on legs 1, 2, 3, 4
Terminal
Size:
Radfordia and Myobia
approximately 400–450 μm
Mycoptes
approximately 350 μm
Tick Identification
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