MITES
Mites are barely visible to the naked eye. The unsegmented abdomen is joined to the cephalothorax with little or no indication of separation.
Life stages are similar to those of ticks. The adults are found in a wide variety of locations and under a wide variety of environmental conditions. Usually, the eggs are deposited on the soil surface, in crevices, or in some instances, under the skin of the host that they infest. The larvae that hatches (six-legged) seeks a blood meal and molts to an eight-legged nymph. More feeding and molting result in adult mites.
Mites can be identified by the specific morphologic structures associated with the end of their legs (pretarsi), their shape, or their host range. One of the important anatomical structures in many mites is the pretarsi which consists of a hook, a stalk (pedicle - above) and a terminal sucker (caruncle - below).
ITCH AND MANGE MITES
Burrowing mange mites
Sarcoptes scabiei (below) - There are numerous varieties which appear to be host-specific. This is a highly contagious organism often transmitted directly by contact. An intense puritis is the most common clinical presentation. Asymptomatic carriers may exist.
Sarcoptes scabiei mites are typically found on parts of the body with less hair such as the hock, elbow or muzzle. Female mites burrow under skin forming tunnels in which they deposit eggs. Larval and nymphal stages develop in these tunnels. After development and mating, adults burrow into new tunnels usually in the stratum corneum. It usually takes about 3 weeks to develop a new generation of mites. The mites are susceptible to drying and can not live more than a day or two off the host.
Peuritis usually does not develop until the skin has become sensitized. Involved area usually show an accumulation of exudate from the inflammation which coagulates to form a crust. Excessive keratinazation and proliferation of connective tissue occurs resulting in thickened skin and hair loss. Secondary infection is common. Diagnosis is by microscopic identification of the mite that is usually obtained by scraping the skin at the outer edges of the lesions. Mineral oil or similar liquids are often used to keep skin particles confined and help confine mites and skin tissue for easier application on a microscope slide.
Histologic evaluation of infested tissue reveals numerous mites in the stratum corneum.
Members of this genus can be identified by the presence of sarcoptiform pretarsi with a long unsegmented caruncle. These are parasites in the skin of mammals and individuals have an anus that is terminal on the ventral side.
There are numerous varieties of this species that infest many animals including man.
Notoedres cati (Feline mange mite). A fairly rare, highly contagious infestation of kittens, cats and rabbits.. Extreme pruritus with secondary self- trauma is common. Lesions are common on the ears, face, and neck. The life cycle is similar to that of Sarcoptes. Lesions are also similar to Sarcoptes being moist in the early stages and as hair loss continues, they become dry and crusty. The first evidence of infestations starts around the tips of the ears and may spread over the head and around the neck, gradually moving more posteriorly.
Members of this genus are similar in appearance to Sarcoptes except that the anus is located on the dorsal surface.
Non-burrowing mange mites
Chorioptes bovis - Foot and tail mange mite (below). - There are many species of this genus that infest a wide variety of animals. The adults can live for weeks off of the host and as such, direct contact is not necessary for spread. Lesions usually start around hooves and spread upward. The involved areas usually become crusty. Members of this genus can be identified by the presence of sarcoptiform pretarsi with a short caruncle. Males have posterior turret-like eminences.
Psoroptes ovis - Scabies mite of sheep (above). All species appear to be host specific. This mite is spread from one individual to another by direct contact. Scab type lesions resulting from inflammation and accumulation of coagulated serum occurs on all parts of the body covered by wool or hair. The wool or hair then becomes loose and falls out or is pulled out by the animal's biting or scratching. The constant irritation often leads to progressive emaciation and finally death. Latent cases are difficult to diagnose. Mites are usually located in the dry crusty areas of the lesions. Individuals of this genus can be identified by the presence of sarcoptiform pretarsi with a long segmented caruncle.
Psoroptes bovis (cattle scabies - above). Lesions first appear on the withers, neck and around the base of the tail, but may spread over the entire body. Scab-like lesions are also present with this species much like those of P. ovis in sheep. Infestations in cattle are a reportable condition in many states.
Psoroptes caniculi (rabbit scabies). Lesions resulting from infestations with this mite are similar to those of P. ovis. The host range includes laboratory rabbits and some species of wild sheep.
Demodex folliculorum - Cigar-shaped mite (above left ). Canine demodecosis is regarded as one of the most important skin diseases of dogs and represents a perplexing treatment problem. Clinical signs may be in one of two forms :1) Scaly form, 2) pustular form. The pustular form may be the result of secondary bacterial infections. Mites may be recovered from most locations in and on the host although the most common location is the hair folicules and subacious glands. Treatment is often difficult and may need to be repeated. Transmission is typically from the dam to young but it is not considered contagious for non-neonatal healthy animals. Reported but rare in felines. Treatment often requires additional antibiotic therapy along with antihistamine therapy. Improved and proper diet often is beneficial. Use of amitraz (Mitaban) has proven successful with no drug reactions related to the product observed.. Although Ivermectin is not approved for use on demodecosis, some reports indicate improvement, especially in extreme clinical cases.Adult onset demodecosis is common in some breeds of dogs representing a difficult manaement problem. Many scientists believe that most dogs (and perhaps humans) are asymptomatic carriers of Demodex sp and it is the change in biologic and physiologic factors that result in clinical disease.
Cheyletiella spp (above). A contagious mite infectious for domestic animals, wildlife, and man. Cheyletiellosis is primarily a dorsal disease manifested by dry or greasy scales. Lesions are mainly over the rump and shoulder regions. Pruritis is variable. Human infestations are common with dermatitis of variable severity. Identification is based on microscopic observation of palpal claws on the recovered mite.
OTHER MITES CAUSING SKIN OR TISSUE IRRITATION
Otodectes cynotis (Ear mite of dogs and cats). Otodectes may account for up to 85% of otitis externa problems in cats and at least 10% in dogs. Clinical signs include irritation, rubbing, scratching and head shaking. A reddish to black, moist, fetid, wax is usually present in ears. Ulceration and granulation may develop in long standing cases. CNS (epileptiform seizures and circling) may occur. Adults are similar in appearance to Chorioptes but without posterior eminences.
Knemidocoptes spp. De-pluming mite and scaly leg mite of poultry (above). Two different species occur but both effect poultry. This mite is also common on the beak and legs of pet and caged birds. It is similar in appearance to Sarcoptes but all members of this genus are parasites of avians.
Eutrombicula alfreddugesi (chigger - above) - Adult chiggers are free living while immature stages are parasitic. Infestations in companion animals is often the result of larval infestations. Pruritis is common around the face, muzzle, thigh, and belly. Clinical signs include pruritus that may persist for several days and a hypersensitivity reaction. Pruritis is generally the result of sensitization to the saliva injected during feeding and occurs after the mite is detached. Supportive treatment is often beneficial.
Neoshogastia americana - Poultry chigger. Infestations with this mite produce a blister-like lesion that reduces the value of market birds. The life cycle similar to that of mammalian chigger.
Dermanyssus gallinae - (red mite of poultry - above) - This mite commonly feed on birds only at night. Cats and dogs may also become infested as a result of contact with poultry. In poultry, irritation and anemia are common, often resulting in poor weight gains, low egg production, etc. Mites can live for months off the host and as such, direct contact is not necessary for the spread of this infestation.
Ornithonyssus sylviarum - Northern fowl mite - This mite is similar to D. gallinae except that it remains on the bird at all times. Clinical signs are also similar to those produced by the red mite, primarily due to blood feeding activities.
Ornithonyssus bursa - Tropical feather mite.
OTHER MITES
Cytodites nudus - This mite is found in respiratory tract and air sacs of poultry. Heavy infestations are often associated with weight loss and respiratory difficulties. At necropsy, white "dots" can be observed on air sac surfaces. Air saculitis is common in heavy infestations.
Pneumonyssus caninum - nasal mite of canines. This is a large mite that can be seen without the aid of magnification. Clinical signs include irritation of the nasal mucosa, sneezing, and head shaking. Infestations with this mite are commonly detected by owners after observing the mites on the nose of dogs.
Harvest and grain mites . This group of mites isconsists of numerous species that live in grain and have been associated with dermatitis in both domestic animals and man. Infestatoins are most common in situations where grain is stored.
Orbatid mites- These are mites that are free-living and are associated with the root-hairs of many plants. Many members of this group act as intermediate hosts for some helminth infections, especially cestodes.
Treatment and control
Sarcoptes in dogs and cats. Animal hair should be clipped around all involved areas and all crusty material removed. Effective acaricides include Amitraz, benzyl bensoite, Ivermectin, lime sulfer, lindane, phosmet, ronnel and rotenone. A second treatment several weeks after the initial treatment is recommended to insure complete control.
A single treatment of Amatraz (mitaban) (10.6 ml in 2 gal water) also works well for Sarcoptes and other sarcoptiform mites. Remember, some of these mites may temporarily infest people. Proper and complete treatment of pet infestations will help prevent human exposure.
Notoedres cati infestations can be treated with lime sulfer. first, wash the cat, then was or dip the animal with a 1:40 solution of lime sulfer in warm water. Treat weekly for at least 6 weeks. Malathion dips (0.5%) also works for this parasite as does treatment with Ivermectin (0.3 micg/kg).
Otodectes sp ear infestations respond to rotonone, thiabendazole and methyl phthalate therapy. Begin by cleaning the ear canal followed by administration of 1-2 ml of mineral oil mixed with thiabendazole or methyl phthalate placed directly in the canal. Massage the treated ear for 30 seconds. Repeat this treatment every 2 to 3 days until mites can no longer be detected.
Demodex sp is susceptible to benzyl benzoate, rotonone, ronnel and cythioate. Infestations with only local involvement can be treated with daily application of ointment. Generalized infestations often respond to Amitraz applied topically as an aqueous suspension (10.6 ml/2 gal water) at 2 week intervals until no mites can be detected. A brood bitch with an asymptomatic Demodex infestation may be bred but it is generally recommended that bitches with active Demodex infestations or a history of infestation be spayed.
Cheyletiella yasguri infestations in dogs can usually be trated with lindane baths or shampoo. Treatment with Amatraz is also usually effective. C. blakei infestations in cats should be treated in a similar manner. This species appears more likely to attack people, especially those that sleep with their pet.
Adult mites are often recovered from fecal examinations of cats even when dermal infestations are not apparent. It may benecessary to treat the entire house or the area inhabited by the infested cat to eliminate this infestation.
Large Animal
Chorioptes sp infestations respond to most standard louse treatments.
Sarcoptes sp infestations in cattle respond to treatment with Ivermectin (2 micg/kg) administered twice over a 7 day period.
Psoroptes sp infestations respond to toxophene and/or Ivermectin treatment. Remember, this is a reportable condition in most states. With any treatment, isolate the infested animal for 2 weeks after treatment. There is generally a 35 day withholding period prior to slaughter. It is also recommednded that the holding facility where the infested animal was maintained be left open for at least 2 weeks.
Psoroptes sp infestations in horses usually respond to lindane treatment given 2 times, 1 week apart. Holding facilities should be left open for 2 weeks.
