The Sarcoptic Mange

Pathology 

Sarcoptic mange or canine scabies is a contagious skin infection characterized by intense pruritus. Other than dogs,  this little mite can also infest foxes and, more rarely rabbits, cats and humans. The aetiological agent is the Sarcoptes scabiei var. Canis, a mite of small size with short and rudimentary limbs. These mites are obligate parasites and complete all their life cycle, which lasts about 3 weeks, on the host’s body. The fecundated female-mite dig galleries inside the horny layer of epidermis where it lays eggs. As it advances into the galleries, it feeds on with keratin detritus and tissular fluid produced because of the irritation. After the hatching, the maggots go back to the cutis surface to complete their maturation.

Sarcoptic mange affects animals of all ages without any predilection for sex or race. Generally, it is passed through direct contact, even if in optimum conditions, it can survive in the environment for some days while still being infesting when not  in contact with the host.

This mite has an incubation period of 1-3 weeks, during which symptoms start to manifest- among them, an intense pruritus which grows in intensity till it becomes unbearable. This particular symptom may indicate a hypersensitivity reaction of type I, II and IV.

The main lesions of the infestation of these mites are characterised by the appearance of papules together with the formation of yellowish crusts located especially on the edge of the auricle, in the elbows and the houghs, in the ventral area of the thorax and abdomen. As the infestation advances, it appears erithema and widespread alopecia by scratching in the whole body.

The diagnosis is made through the microscopic analysis of cutaneous scrapings for the search of adult mites, eggs or faeces. However, since few individuals are sufficient to cause serious reaction, it is difficult to determine their presence.

The diagnosis is confirmed by the finding of mites, eggs, faeces in the scrapings. The scraping must be done superficially but on wide cutaneous areas (for example on the whole auricle), in order to collect a lot of squamas and keratin detritus. Generally there are very few mites, and the scrapings are often negative. The diagnosis could also be confirmed by the response to the therapy. The histological test of a cutaneous biopsy can suggest ectoparasitosis, due to the presence of eosinophilic pustules, and sometimes can diagnose mange, when mites are included in the section. Recently, a serological test for the detection through ELISA method of the antibodies IgG specific for Sarcoptes has been developed. This test is very sensitive and useful for the identification of the infestation in minor cases, or with immunodepressed animals which do not show pruritous, even if they host parasites.

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