Mange / Demodecosis

Dr Mc Blog


August 27, 2014
People love the word “mange”. “He’s just a mangey old alley cat” someone will say. Used as a description for a pet with scruffy fur or unsightly skin, most people don’t realize that mange is a group of very specific skin diseases caused by parasitic mites. There are different sorts of mites, all possessing eight legs and often only visible under a microscope. There are two kinds that commonly affect the dog.

Sarcoptic mange is caused by an ugly little mite, sarcotes scabei, that burrows into the skin of both dogs and people. Often called “scabies”, it is feared primarily because of its transmission both from dogs to people and between people. Excellent treatment protocols are available for this disease.

Demodex or demodectic mange is an entirely different skin disease. First, it is NOT contagious to other pets or people. Second, the demodex canis mite burrows very deeply into the hair follicles of the skin and is sometimes harder to treat than sarcoptic mange. Puppies contract it while nursing from their mothers (strange but true). There is some thought of either an inherited predisposition or a depressed immune system allowing the pups to express the disease visually, as not all pups in a litter may be affected. When first seen, a puppy may display only a bare patch around one eye. It’s not painful and doesn’t itch, but usually looks so unsightly that it causes immediate alarm. Often the mite doesn’t show up until the pup is over six months of age, which confounded scientists trying to understand the connection between exposure and disease expression for years. For some puppies the disease can be far worse than an unsightly bald patch. The entire body may lose hair in a case of generalized demodecosis, with scabs and sores erupting as a secondary bacterial infection kicks in. Edema and swelling of the face and feet are common, making a pup truly miserable. These puppies are extremely ill, their immune system is gravely compromised and some may die.

Because the skin can only react in a limited number of ways to any disease, signs of hair loss, open sores and itching can be caused by a variety of problems : other parasites, allergies, staph and other bacterial infections, fungal infections. A veterinarian needs to examine your pet to make the correct diagnosis. A skin scraping is diagnostic for demodex- but not always for sarcoptes. A sharp blade is used to literally scrape any potential mites off the skin and the slide is examined under the microscope. Positives are slides that wiggle back at you!

Fortunately, there are several treatment options available for demodectic mange. Thirty years ago a breakthrough dip was discovered, which revolutionized the old “cover ‘em in tar” treatment. Today that dip is less frequently used as new oral and topical medications have been developed, which when combined with antibiotics and medicated shampoo treatment protocols have greatly improved the cure rate for this disease. Once treated, dogs are cured of demodex, though if allowed to breed there is a strong risk they will pass it on to some of their offspring.

Perhaps my most memorable suspect demodex case occurred a few years back. The young German Shorthair Pointer presented with some hair loss around her muzzle. The skin scraping was negative, so I started a fungal culture for ringworm. Cultures take about two weeks to run their course. When the ringworm culture was negative, the Pointer returned for a recheck. The lesions were spreading, red sores and deep cracks tracing from the bridge of her nose down the sides of her face and lips. The rash was especially bad just below her eyes, though her eyelids were surprisingly clear, the skin untouched by disease. The rest of her coat remained beautiful. I again did a skin scraping, and when negative, repeated the test. Negative. Convinced as I was that this must be demodex, I told the owner that we would start therapy immediately before this could spread further.

When I next saw the dog she was the picture of health. Her face was completely clear, new hair growing in on smooth skin. I glowed. Success is wonderful. It was the client, of course, who set me straight. A bachelor who did most of his own cooking, and not too elaborate, thank you, he frequently fixed up a can of beans. Seems the Pointer liked beans too, straight from the can. He caught her burying her nose in deep to reach that last drop.  Her face cleared up as soon as he found another disposal system for the cans. My antibiotics probably helped the secondary infection but there was no denying that my years of training had let me down. The medical texts on mange variations do not mention bean-can-itis.

Christine B. McFadden, DVM

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