Mite Induced Dermatitis


Bat Mites Bite Humans
ventral view. (From Strandtmann and Wharton, 1958.)

to their bat hosts, Chiroptonyssus robustipes has been known to cause the death of heavily infested, captive Brazilian free-tailed bats (Tadarida brasiliensis). This mite attaches primarily to the wings, where its feeding can result in increased vascularity and edema at the bite sites, enlargement of lymphatic vessels, hyperkeratosis, and excoriation of the stratum corneum (Sweatman, 1971 ).

A few macronyssid mites have invaded the oral mucosa of pollen-feeding and fruit-feeding bats (Psyllostom-atidae). All are members of the genus Radfordiella (Fig. 23.24). In heavily infested bats they can cause bone damage to the hard palate and destruction of gingival tissues, resulting in loss of teeth. The damage is caused by protonymphs. The adult mites presumably are nidicolous and move onto the host only intermittently to feed on parts of the body other than the mouth (Phillips et al., 1969).

Tropical rat mite (Ornithonyssus bacoti)

The tropical rat mite (Fig. 23.6) occurs throughout the world, where it parasitizes primarily rodents. It occasionally infests cats, wild carnivores, chickens and other birds, and humans. Most veterinary problems involving this mite occur in laboratory mice, rats, and hamsters. Heavily infested animals may become debilitated and anemic or experience reduced reproductivity; death can occur in some cases. Infestations usually are recognized by the presence of blood-engorged deutonymphs and adults in the animal bedding, cages, and corners or crevices of cage racks. The tropical rate mite is a vector of Litomosoides carinii, a filarial nematode in cotton rats (see under Mite-Borne Diseases).

Blood-fed females lay their eggs in bedding or nest debris of their hosts and in cracks and crevices. The eggs hatch in 1—4 days, producing larvae that molt to protonymphs about 1 day later without feeding. The protonymphs feed on blood, molting to deutonymphs in 1—2 weeks. Deutonymphs molt to adults after 1—2 days without feeding. Development from egg to adult can be completed in 11 — 16 days under favorable conditions. Adults usually mate within 1 —2 days following emergence and can survive several days to a few weeks without a blood meal. The tropical rat mite is found primarily in rodent nests, moving onto the host animals only to feed.

Tropical fowl mite (Ornithonyssus bursa)

The tropical fowl mite (Fig. 23.7) is a common ectoparasite of wild and domestic birds throughout the warmer regions of the world. Domestic or peridomes-tic birds which may be infested include chickens, ducks, pigeons, starlings, house sparrows, and canaries. Most infestations originate from contact with wild birds or infested nest materials. Heavy infestations in chickens and other domestic fowl can result in anemia, decreased weight gain and egg production, and occasionally death. Newly hatched chicks and young birds are especially vulnerable. Blood-feeding by this mite causes skin irritation that may be intense enough to induce setting hens to leave their nests. Inspection of the plumage will reveal the mites in the down feathers, particularly around or just below the vent. Infested feathers are soiled or dirty in appearance due to the accumulation of mites, exuviae, eggs, and excreta. In the case of young birds, the mite commonly occurs around the eyes and beak.

O. bursa may cause more problems for wild birds than previously suspected. In Denmark, for example, nest infestations of the barn swallow (Hirundo rustica) have been shown to decrease reproductive success by reducing clutch sizes, nesting periods, and number of fledglings and by lengthening the time between clutches and the incubation period (Möller, 1990). Barn swallows regularly reuse old nests but tend to avoid nests infested with this mite.

The tropical fowl mite lays its eggs on the host or in nesting materials, where they hatch in 2—3 days. The larvae do not feed, whereas the protonymphs and adults feed intermittentiy on host blood. Although relatively few details about its life history have been reported, this mite is believed to develop from egg to adult in 6—8 days. In the absence of a host, it can survive about 10 days.

Northern fowl mite (Ornithonyssus sylviarum)

The northern fowl mite (Fig. 23.8) is a major pest of chickens and other domestic fowl, particularly in temperate regions of North America and Eurasia. It also is an economic pest of domestic fowl in Australia, New Zealand, and other parts of the world where it has been introduced. In addition to infesting chickens, it is commonly found in the nests of pigeons and various wild birds and as an incidental pest biting rodents, hamsters, and humans.

The greatest economic impact occurs in chicken houses. Initial infestations usually occur via wild birds or newly acquired chickens already infested with the mite. They can then spread throughout even the largest houses within a few weeks. The northern fowl mite causes problems very similar to those caused by O. bursa. These include skin irritation without apparent lesions at the bite sites; matted and grayish feathers, especially around the vent where the mites, their exuviae, and feces are concentrated (Eig. 23.25); scaly, scabby, or thickened skin; and general loss of thrifti-ness. Individual caged birds may have 10,000 or more mites. Heavily infested birds often become anemic, experience decreased weight gains and egg production, and sometimes die. Eggshells may become significantly thickened, and egg production may drop 5— 15% compared to uninfested birds. The greatest effect on body weight and efficiency of feed conversion generally occurs when hens are infested with mites before they reach full egg production. Although pathogens of poultry, such as viruses that cause Newcastle disease and fowlpox, have been recovered from O. sylviarum after feeding on infected chickens, there is little or no evidence that the mite transmits these agents when it bites.

The northern fowl mite spends most of its time on the host. It also occurs, however, in nesting materials and nest debris, roosting areas, cracks and crevices in the floors, and walls of chicken houses, where they can be found during the day or night. Oviposition

FIGURE 23.25 Northern fowl mite, Ornithmyssus sylviarum (Macronyssidae); heavy infestation of chicken in vent area. (Photo by Jerry F. Butler.)

usually occurs on the host about 2 days following complete engorgement with blood. Eggs typically are laid two or three at a time, but there may be as many as five. The eggs hatch in about 24 hr. The protonymph, the only immature stage that feeds on blood, requires at least two feedings before it molts to produce the deutonymph. The complete life cycle is typically 5—7 days, enabling populations to build very rapidly. Survival time without a host is usually 3—4 days but may be as long as 2—3 weeks.

Snake mite (Ophionyssus natricis) This mite (Fig. 23.9) is a common parasite on captive snakes, where it is usually found around the eyes and under chin scales. It also may be found on captive lizards and other reptiles. It behaves much like a nest parasite and is believed to have evolved from a mite associated with rodents. The sources of infestation are usually caged snakes in pet stores, zoos, or laboratories. Although O. natricis occasionally is found in low numbers (< 100 per host) on wild snakes, its populations on captive snakes may reach hundreds or thousands per host. Heavy infestations cause listless behavior, loss of appetite, anemia, skin irritation, loss of scales, and, in some cases, death. Several hundred mites are sufficient to cause severe anemia and other symptoms.

O, natricis is a vector of the bacterium Aeromonas hydrophila that causes hemorrhagic septicemia in snakes. Infected snakes hemorrhage internally and often die 3— 4 days following infection.

The snake mite lays its eggs in crevices, debris, and on rough surfaces of cages, where they hatch in 2—4 days. The larvae do not feed, whereas the protonymphs and adults are obligate parasites that feed exclusively on blood. The life cycle usually is completed in 2—3 weeks at room temperature, with adult females living 5-6 weeks. Females typically feed 2 or 3 times, depositing about 20—25 eggs after each blood meal. See Camin (1953) for further details on the biology and behavior of this mite.


Laelapid mites are commonly associated with rodents, other nest-building mammals, and bird nests. Those of medical or veterinary concern belong to the subfamilies Laelapinae and Haemogamasinae, which includes both facultative and obligate parasites that generally cause little or no apparent harm to their hosts. The genera most commonly encountered by veterinarians are Androlaelaps, Haemogamasus, and Laelaps. Haemogamasus liponyssoides is an opportunistic blood feeder that inhabits nests of rodents and shrews. Its slender, chelate chelicerae are capable of piercing skin to feed on blood, enabling this mite to feed on laboratory mice if they become infested.

Chicken Mite

FIGURE 23.25 Northern fowl mite, Ornithmyssus sylviarum (Macronyssidae); heavy infestation of chicken in vent area. (Photo by Jerry F. Butler.)

Spiny rat mite (Laelaps echidninus)

The spiny rate mite occurs throughout most of the world as an ectoparasite associated primarily with the Black and Norway rats. Occasionally it is found on Sigmodon and Rattus species, the house mouse, and other domestic and wild rodents. It is rarely found on laboratory animals. This mite is generally easy to recognize by its large body size (ca. 1 mm long), heavy sclerotization, and long, stout body setae that give it a spiny appearance. It lives primarily in host bedding or nesting materials, moving onto the host at night to feed. Its chelicerae are not capable of piercing intact skin but instead assist the mite in feeding on lachrymal secretions and blood or serous exudates from abraded skin. Rarely does its feeding cause discernible lesions, although injury to the footpads of suckling mice has been reported. The spiny rat mite is a vector for two blood-protozoan parasites, Hepatozoon muris of rats and H. griseisciuri of the gray squirrel (Sciurus caro-linensis).

Regular blood meals are required for L. echidninus to survive and reproduce. Blood-fed females give birth to live larvae which do not feed. The protonymphs and deutonymphs both apparently feed similarly to adults, completing their development to adults in 1—3 weeks. The length of their life cycle is variable, requiring at least 16 days. The females can live 2—3 months; without food, however, they survive only about a week.


Although not widely recognized as a problem, larvae of trombiculid mites (chiggers) commonly infest domestic animals. Only in cases of heavy infestation or sensitivity reactions are they likely to be brought to the attention of veterinarians. As in humans, the resultant dermatitis is a response to chiggers that are normally parasitic on other host animals. Only incidentally do they attach to atypical hosts such as cats, dogs, sheep, other livestock, or, occasionally, to domestic or pet birds. Most cases involve mild pruritus and are likely to go unnoticed. Cases of heavy infestations, however, can result in severe itching with formation of vesicles and crusty or scabby skin lesions, usually about the head and neck. Large numbers of engorged chiggers may be visible as orange patches associated with the lesions. The chiggers typically remain attached only up to 2-3 days. Treating the lesions with an acaricide and preventing secondary infection usually resolves the problem if the animal is not reinfested.

Some chiggers enter the skin via large hair follicles, crawling down the shaft of the hair, sometimes well beneath the skin surface. An extension of the stylostome, or feeding tube, may extend backward around the mite to form a hyaline capsule. Usually these capsule-forming chiggers are completely intradermal and may cause localized inflammation and edema. In some cases they induce formation of cysts at the base of the hair follicles that can lead to secondary infections and slow-healing lesions. Intradermal chiggers include members of the trombiculid genera Cheladonta,Euschoengastia, Gahrliepia, Guntheria, Intercutestrix, and Schoutedenichia (Sweatman, 1971). These mites occur primarily in Southeast Asia, the South Pacific islands, Australia, Africa, and other parts of the Old World. Rodents, shrews, and bandicoots are some of their more common natural hosts.

A few species of chiggers have been identified as the cause of trombiculosis in domestic cats. In the United States, Walchia americana is known to cause papules on the face, ears, and thoracic areas of cats, in addition to thickening and crusting of the skin on the abdomen and legs. This is accompanied by hyperkeratosis, eosinophilia, and infiltration of mast cells, as evidenced in sldn biopsies at the lesion site (Lowenstine et al., 1979). Large numbers of Eutrombicula alfreddugesi have been observed as distinct orange patches on the head and ears of a cat in North Carolina (USA), causing inapparent dermatitis (Hardison, 1977). Other chiggers known to infest cats are Odontacarus adelaidiae, O. australiensis, Schoengastia philippinensis, and S. westraliensis in Australia. Natural hosts for these mites include wallabies, grey kangaroos, and wild pigs (Wilson-Hanson and Prescott, 1985). Other cases in cats involving unidentified chigger species have been reported in Australia. Lesions occurred as pinpoint erythemas and orange crusts on the ears (pinnae), pruritus, papules and orange crusty lesions about the eyes and face, conjunctivitis, and ocular discharges. In one case, swelling and irritation of the perineal region with concomitant inability to pass urine was attributed to trombiculid mites (Wilson-Hanson and Prescott, 1985).

Dogs appear to be less commonly bothered by chiggers. Bite reactions are similar to those of other host animals, with localized redness, pruritus, and development of papules or vesicles at the bite sites. Cases involving heavy infestations may warrant veterinary attention. In Europe, the harvest mite (Neotrombicula autumnalis) reportedly has caused nervous symptoms in dogs, including partial paralysis of the limbs and lameness (Prosl et al., 1985).

Virtually all species of livestock are subject to chigger infestations while grazing, walking paths to and from barns, or being held in enclosures or by contact with recently harvested hay or grains infested by these mites. Skin lesions in the form of papules or crusty eruptions can be irritating and lead to self-inflicted skin damage as the host animal rubs and abrades the affected areas. Lesions occur primarily on the lips, muzzle, face, feet, and belly. Pigs have developed a generalized pruritus after feeding on fresh, chigger-infested grains from automatic feeders. Sheep, goats, and cattle are particularly prone to infestations with N. autumnalis in Europe during the harvest season; this mite causes pruritus, scabs, and loss of hair, particularly about the head and neck. In Australia, sheep have experienced severe dermatitis on the legs and feet due to infestations by Eutrombicula sarcina, a chigger that normally parasitizes kangaroos. An orflike condition in sheep, caused by a Guntheria species, has been reported during the summer months in South Africa (Otto and Jordaan, 1992).

Domestic birds such as chickens may become parasitized by chiggers (e.g., Neoschoengastia americana), leading to itching and dermatitis. In most cases the mites can be found under the wings or around the vent. Reports of anemia in chickens attributed to heavy infestations of chiggers should be treated with skepticism; chiggers feed on dermal tissues and not on blood. Occasionally other captive birds may be affected. A chronic infestation of canaries by an unidentified trombiculid mite has been reported in Australia. The canaries, in a commercial aviary, developed nonpruritic, subcutaneous swellings of the legs and ventral trunk, with acute inflammation and skin necrosis at the sites of mite attachment (Pass and Sue, 1983).

Wild animals generally do not show adverse reactions to chiggers, even when heavily infested. Occasionally, however, they do react severely to bites of certain species that normally parasitize other hosts. Reactions include formation of vesicular or crusty lesions, slow-healing eschars, localized skin discoloration, and some loss of hair. Examinations often reveal orange or red clusters of mites about the head, ears, neck, axillae, or groin. Sometimes infestations of chiggers about the eyes cause ocular lesions in the form of pruritic eyelids and conjunctivitis. Snakes, lizards, skinks, and other reptiles are parasitized by chiggers, most commonly noticed as orange or red clusters of mites on the head and neck. The host seldom shows apparent harm, even in cases of individual snakes infested with several thousand mites.

Fur Mites

Certain families of mites are categorized as fur mites because they are specially adapted for living in the hair coat of mammalian hosts. They often exhibit striking modifications of the palps, legs, and other body structures for grasping or clinging to hair. The five groups of particular veterinary interest are the cheyletoid families Cheyleti-dae (including the former family Cheyletiellidae) and Myobiidae and the astigmatid families Listrophoridae, Atopomelidae, and Myocoptidae.


Parasitic cheyletid mites occur on domestic cats, dogs, and rabbits, as well as many wild mammals and birds. They are nonburrowing mites that live in the pelage of their hosts and feed on lymph and other tissue fluids by piercing the epidermis with their stylet-like chelicerae. The enlarged gnathosoma and pair of large, terminal palpal claws give cheyletid mites a characteristic appearance. These structures are used to secure the mites to their hosts and to assist them in inserting their chelicerae. Members of the genus Cheyletiella can cause problems that warrant veterinary attention. Although most cases of cheyletiellosis go unnoticed, infestations of these mites can cause eczema-like skin conditions, or cheyletid mange, with associated pruritus and hair loss. Three Cheyletiella species of veterinary importance are Cheyletiella blakei of cats (Fig. 23.26), C. yasguri of dogs, and C. parasitivo-rax of rabbits (Fig. 23.27). All developmental stages of these mites occur on the host animal. The eggs are glued to hairs but can be dislodged with loose hairs by host grooming. They also can be ingested and passed in the feces. The presence of Cheyletiella eggs in cat and dog feces thus serves as evidence of mite infestations even in asymptomatic cases (Fox and Hewes, 1976; McGarry, 1993). Transmission is usually by direct contact with infested animals, including maternal transfer while nursing. Because Cheyletiella species can survive up to 10 days or more off a host, animal bedding, household furniture, blankets, and carpets frequented by pets can serve as other sources of these mites. Cheyletiella mites are commonly phoretic on cat and dog fleas (Ctenocephalides spp.) and also may be transmitted via these ectoparasites.

C. blakei usually infests the facial area of cats. Heavy infestations can result in the formation of small, crusty, erythematous papules and loss of hair, accompanied by itching and scratching. Long-haired cats tend to be more commonly infested than short-haired cats and are more likely to be involved in human cases of cheyletiellosis. C. yasguri parasitizes domestic dogs, particularly in Europe and North America. It is generally less common than C. blakei and only occasionally causes problems warranting veterinary attention. Signs of an infestation are scratching and a mealy or powdery dandruff in the affected areas, commonly the lower back. Heavy infestations can cause scaling, hyperkeratosis and thickening of the skin, erythema, pruritus, and hair loss. Puppies tend to have a higher incidence of C. yasguri than do adult dogs and are more likely to exhibit pruritus. This mite can cause dermatitis in humans upon close contact with infested dogs, especially puppies (Fig. 23.28). Acaricidal treatments of dogs and their surroundings are effective in controlling C. yasguri. This is especially important in kennels, which serve as a common source of mite infestations.

Northern Fowl Mites HumansMyxomatosis Facts And Figures

FIGURE 23.29 Mouse for mite, Myobia musculi (Myobiidae), female, dorsal view. (From Baker et al., 1956.)

Radfordia Ensifera

FIGURE 23.30 Radfordia ensifera (Myobiidae), female, dorsal view. (From Baker et al., 1956.)

exudates and hairless patches in which the mites can be found in the disrupted keratin layer amidst epidermal debris. Infestations of C. parasitivorax are particularly a problem in commercial rabbit colonies and laboratories where rabbits are closely confined. Wild rabbits seldom exhibit cheyletiellid mange. C. parasitivorax is capable of transmitting myxomatosis virus among European rabbits in Australia.

Eor additional information on Cheyletiella species and their veterinary importance, see Smiley (1970) and van Bronswijk et al. (1976).


Members of the family Myobiidae are obligate parasites of rodents, bats, insectivores, and certain marsupials. They typically grasp the hairs of their host with their forelegs, which are often highly modified for this purpose. The mites move up and down the hair shaft and remain clinging to the hairs as they feed on epidermal fluids. Their chelicerae are long and stylet-like and adapted for puncturing thin epidermal tissues to feed on extracellular fluids. A few species, however, are known to feed on blood (e.g., Blarinobia simplex on shrews and Eadiea brevi-hamata on the shrew-mole). Most species cause litde apparent discomfort or harm to their hosts, even when mite populations are high. Exceptions of veterinary interest are a few Myobia and Radfordia species that commonly infest rats and mice, often causing mild dermatitis and scurfiness in laboratory rodents.

The most widely recognized myobiid is the mouse fur mite, Myobia musculi (Fig. 23.29). This is a cosmopolitan, ubiquitous species that infests the pelage of both wild and captive house mice {Mus musculus). Most of what is known about the development and biology of myobi-ids is based on this species. Females deposit their eggs singly, gluing them to the bases of hair shafts. The developmental time from egg hatch to adult is about 23 days. All stages, including tire larvae, feed on dermal tissue fluids. The host response varies greatly depending on the strain, sex, age, and sensitivity differences of individual mice. Lighdy infested hosts are often asymptomatic or exhibit litde adverse reaction. In highly sensitive hosts, however, even a few mites can elicit allergic reactions and severe pathologic responses. Heavy infestations can lead to severe dermatitis, with intense pruritus, hair loss, self-inflicted trauma from scratching, and, in some cases, death. This especially can be a problem in laboratory mice colonies where infestations are likely to involve virtually all individuals.

Two Radfordia species occur worldwide, infesting the fur of wild and laboratory rodents. The more common is Radfordia ensifera, parasitic on rats (Fig. 23.30); the other is R. affinis, parasitic on the house mouse. They

FIGURE 23.29 Mouse for mite, Myobia musculi (Myobiidae), female, dorsal view. (From Baker et al., 1956.)

closely resemble Myobia musculi, from which they are distinguished by a pair of tarsal claws (rather than one claw) on the second leg. Although they generally cause litde pathologic effect, dermatitis and self-inflicted trauma have been associated with heavy infestations of R. ensifera on laboratory rats,

FIGURE 23.30 Radfordia ensifera (Myobiidae), female, dorsal view. (From Baker et al., 1956.)

Cheyletiella MiteRadfordia Ensifera
FIGURE 23.33 Analges chelopus (Analgidae), ventral views. (A) Female; (B) male. (From Gaud and Atyeo, 1996.)

FIGURE 23.36 Longipedia tricalcamta (Syringobiidae), female, ventral view. (From Gaud and Atyeo, 1996.)

ventral view. (From Gaud and Atyeo, 1996.)

and occasionally causes pityriasis in chickens, whereas E. odontophori has been reported to cause mange in African birds. Microlichus avus and M. americanus are known to produce crateriform skin lesions and severe mange in several avian species. Myiases species (e.g., Myiases macdonaldi) may invade the outermost skin layers to produce pityriasis and mange, sometimes severe enough to cause feather loss. Heavy infestations of Rivoltasia bifurcata on chickens can result in intense itching and pityriasis, especially involving the head. For further information on these and other epidermoptid genera of veterinary interest, see Fain (1965) and Krantz (1978).


Knemidokoptid mites superficially resemble sarcoptids, from which they differ by having short legs without

FIGURE 23.36 Longipedia tricalcamta (Syringobiidae), female, ventral view. (From Gaud and Atyeo, 1996.)

pretarsi or long setae and by lacking dorsal triangular setae. They invade the feather follicles and skin of wild and domestic birds worldwide, causing knemidokoptic mange in some species. Their life cycle is similar to that of Sarcoptes scabiei. All stages of these mites occur on the host, and transmission is by direct contact with infested birds. There are several species of veterinary importance: Knemidokoptes mutans and Neocnemidocoptesgallinae infesting poultry, K. pilae infesting parakeets, and K. ja-maicensismitstmg passerine birds, including canaries.

Scaly-leg mite (Knemidokoptes mutans) This mite (Fig. 23.39) is a pest of poultry, especially chickens, in North America, Europe, and Africa and probably occurs worldwide. It burrows beneath the epidermal scales of the legs and feet, causing irritation, inflammation, hyperkeratization, formation of vesicles, and encrustations (Fig. 23.40). The crusts may cover entire limbs, hence the term scaly-leg, a condition most commonly seen in older birds. In chronic cases, infestations can lead to lameness, deformed legs and feet, and occasionally the loss of digits. The skin of the comb and


FIGURE 23.38 Epidermoptcs bilobatus (Epidermopridae), female, ventral view. (From Gaud and Atyeo, 1996.)

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