Demodex is a mite that lives naturally in the hair follicles of many mammalian species. In normal dogs small numbers of Demodex canis mites live unobtrusively as part of the host's normal fauna. Demodicosis is the condition resulting from a proliferation of these mites. Veterinarians categorize demodicosis as localized or generalized.
Dogs affected with localized demodicosis have one or more small patches of hair loss, often on the head or forelimbs. These lesions may be reddened and slightly scaly and may or may not be itchy. Localized demodicosis usually occurs in dogs between three and twelve months of age. Onset often accompanies puberty. While owners and some veterinarians are anxious to treat any dog presenting with localized demodicosis, rarely is this justified. Greater than 90% of these cases resolve spontaneously within four to eight weeks and almost never recur.
Generalized demodicosis is a much more severe and potentially life threatening disease. Lesions appear over much of the dog's body, often associated with deep bacterial infections. This form of demodicosis is universally thought to be associated with a genetic predisposition to a specific type of immunodeficiency. Adult onset can be associated with neoplasia or other life threatening disease. Treatment is extended and often must be continued for life since relapses are quite common.
Amitraz (in the form of a dip) is the only FDA approved effective product for treatment of demodicosis and should be reserved for the generalized form of this disease. Indiscriminate use of this agent for speeding elimination of mild localized demodicosis increases the risk of developing resistant mites.
In the recent past owners were routinely counseled by veterinarians to spay or neuter any dog affected with either form of demodicosis. It is now generally accepted that while certain breeds are predisposed to demodicosis, any dog can break with the localized form and need not necessarily be removed from a well-conceived breeding program. Certainly, those dogs affected with the generalized form should be spayed or neutered.
Dr. Susanne Hughes