Demodicosis

Demodicosis
Classification and external resources
A dog with severe demodectic mange
ICD-10	B88.0 (ILDS B88.020)
ICD-9	133.8
DiseasesDB	33039
eMedicine	article/1203895

Demodicosis, also called demodectic mange or red mange, is caused by a sensitivity to and overpopulation of Demodex canis as the animal's immune system is unable to keep the mites under control.

Demodex is a genus of mite in the family Demodicidae. Demodex canis occurs naturally in the hair follicles of most dogs in low numbers around the face and other areas of the body. In most dogs, these mites never cause problems. However, in certain situations, such as an under-developed or impaired immune system, intense stress, or malnutrition, the mites can reproduce rapidly, causing symptoms in sensitive dogs that range from mild irritation and hair loss on a small patch of skin to severe and widespread inflammation, secondary infection, and—in rare cases—a life-threatening condition. Small patches of demodicosis often correct themselves over time as the dog's immune system matures, although treatment is usually recommended.

Presentation

Minor cases of demodectic mange usually do not cause much itching but might cause pustules on the dog's skin, redness, scaling, hair loss, or any combination of these. It most commonly appears first on the face, around the eyes, or at the corners of the mouth, and on the forelimbs and paws.

In the more severe form, hair loss can occur in patches all over the body and might be accompanied by crusting, pain, enlarged lymph nodes, and deep skin infections.

Demodex canis

Demodectic mange is transmitted from host to host through direct contact. Typically animals become infected through nursing from their mother. Demodex mites are host-adapted; there is no zoonotic potential in either canine or feline demodicosis. ^[1] These mites (Demodex canis) thrive only on their specific hosts (dogs). The transmission of these mites from mother to pup is normal (which is why the mites are normal inhabitants of the dog's skin), but some individuals are sensitive to the mites due to a cellular immune deficiency, underlying disease, stress, or malnutrition ^[1], which can lead to the development of clinical demodectic mange.

These diseases in humans is usually caused by Demodex folliculorum (not the same species affecting dogs)and is usually called demodicosis which may have a rosacea-like appearance.^[2][3] Common symptoms include hair loss, itching and inflammation. An association with pityriasis folliculorum has also been described.^[3]

Some breeds appear to have an increased risk of mild cases as young dogs, including the Afghan Hound, American Staffordshire Terrier, Boston Terrier, Boxer, Chihuahua, Chow Chow, Shar Pei, Collie, Dalmatian, Doberman Pinscher, Bulldog, English Bull Terrier, Miniature Bull Terrier, German Shepherd Dog, Great Dane, Old English Sheepdog, American Pit Bull Terrier, West Highland White Terrier, Rat Terrier, and Pug.

Demodectic mange also occurs in other domestic and wild animals. The mites are specific to their hosts, and each mammal species is host to one or two unique species of Demodex mites. There are two types of demodectic mange in cats. Demodex cati causes follicular mange, similar to that seen in dogs, though it is much less common. Demodex gatoi is a more superficial form of mange, causes an itchy skin condition, and is contagious amongst cats. It has recently manifested itself in mountain lions in the Rocky Mountain region. The DNR has reported an outbreak or epidemic within the Utah County area. These infected and mange-ridden cats are being shot on sight.

Treatment

Localized demodectic mange is considered a common puppyhood ailment, with roughly 90% of cases resolving on their own with no treatment. Minor, localized cases should be left to resolve on their own to prevent masking of the more severe generalized form. If treatment is deemed necessary Goodwinol, a rotenone-based insecticide ointment is often prescribed, but it can be irritating to the skin. Demodectic mange with secondary infection is treated with antibiotics and medicated shampoos.

In more severe generalized cases, Amitraz is a parasiticidal dip that is licensed for use in many countries (the only FDA approved treatment in the USA) for treating canine demodicosis. It is applied weekly or biweekly, for several weeks, until no mites can be detected by skin scrapings. Demodectic mange in dogs can also be managed with avermectins, although there are few countries which license these drugs, which are given by mouth, daily, for this use. Ivermectin is used most frequently; collie-like herding breeds often do not tolerate this drug due to a defect in the blood-brain barrier, though not all of them have this defect. Other avermectin drugs that can be used include doramectin and milbemycin.

Cats with Demodex gatoi must be treated with weekly or bi-weekly sulfurated lime rinses. Demodex cati are treated similarly to canine demodicosis.

Because of the possibility of the immune deficiency being an inherited trait many veterinarians believe that all puppies with generalized demodex should be spayed or neutered and not reproduce. Females with generalized demodex should be spayed because the stress of the estrus cycle will often bring on a fresh wave of clinical signs.

Diagnosis

For demodectic mange, properly performed deep skin scrapings generally allow the veterinarian to identify the microscopic mites. However because the mite is a normal inhabitant of the dog's skin, the presence of the mites does not conclusively mean the dog suffers from demodex. Rather abnormally high numbers of the mite are more useful. In breeds such as the West Highland White Terrier, relatively minor skin irritation which would otherwise be considered allergy should be carefully scraped because of the predilection of these dogs to demodectic mange. Skin scrapings may be used to follow the progress of treatment in demodectic mange.

References

1. ^ ^{a b} [1], Companion Animal Parasite Control.
2. ^ Baima, B.; Sticherling, M. (2002). "Demodicidosis Revisited". Acta Dermato-Venereologica 82 (1): 3–6. doi:10.1080/000155502753600795. PMID 12013194. 
3. ^ ^{a b} Hsu, Chao-Kai; Hsu, Mark Ming-Long; Lee, Julia Yu-Yun (2009). "Demodicosis: A clinicopathological study". Journal of the American Academy of Dermatology 60 (3): 453–62. doi:10.1016/j.jaad.2008.10.058. PMID 19231642. 

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