Scabies & Mange
Scabies is the name for a skin disease caused by a member of the Sarcoptes genera of mite parasites. Another name for scabies is "sarcoptic mange". Scabies is normally an intensely uncomfortable skin disease due to itchiness (pruritus) caused by the parasite. This pruritus is thought to be due to a hypersensitivity to proteins found in the fecal matter produced by Sarcoptes mites as they burrow through the layers of the epidermis. The classic case of canine scabies is an intensely pruritic dog who scratches and rubs almost constantly and who cannot seem to be comfortable.
What is the pinnal-pedal reflex?
Classically, when the ear flaps (pinnae) of a dog with scabies are gently rubbed, the dog's hind leg will start a scratching motion, because the pinnae are extremely itchy in most infested dogs. However, the author has seen confirmed cases of scabies in which no pinnal-pedal reflex was present. In addition, the pinnal-pedal reflex can be found in dogs that have extreme pruritus from other disorders such as severe food allergy (adverse food reaction).
How is scabies diagnosed?
The easiest diagnosis is when scabies mites, eggs, or scabies fecal pellets are found on skin scrapings. However, it is widely known among dermatologists that some dogs with scabies have relatively few mites even though their symptoms are severe. This may be due to the hypersensitivity (e.g. allergic tendency) of some dogs to the infestation. I.e., a small number of mites can cause severe disease in some individuals and it is a matter of chance that mites are picked up on skin scrapings (the main diagnostic test for skin mites).
What is done if mites are not found?
If the patient's history includes risk factors or classic lesion locations, many veterinarians will recommend treatment of scabies mites as both a diagnostic test and also a therapy. Risk factors include having wild or stray animals (especially but not limited to foxes) in the pet’s outdoor environment, other pruritic (potentially infested) dogs in the home, or history of intense pruritus developing within 2-3 weeks after exposure to an infested dog such as could occur in a kennel, a grooming establishment, pet day care, or veterinary hospital. Having another dog in the household without symptoms does not rule out scabies. I have found scabies mites on scrapings from dogs with housemates who did not have symptoms. Scabies should be considered if a dog who has never had significant skin problems becomes intensely pruritic to the point of scratching until the skin is raw or bleeding. (What a poor dog!)
Classic lesion locations include the pinnae and extremities including the elbows, hocks (the canine equivalent of the ankles). Other lesion locations include the area of the sternum (breast bone) and belly. Lesions seen on the skin are usually due to self-trauma from scratching and rubbing. Sometimes many tiny red bumps/pimples (papules) may be seen.
Because the symptoms of scabies are almost exactly the same as severe allergies, many dermatologists recommend treatment for scabies as part of a routine workup for pets with significant pruritus. It is better to treat for scabies early on in the diagnostic process to be sure that is not the problem. Looking at it another way, there are not many truly curable disorders like scabies and it would be unfortunate to miss an opportunity to cure!
Where no mites are found on the pruritic dog but treatment for scabies is recommended based on suspicion (see above), all contact dogs should be treated. More time, effort, and expense is involved with treating all dogs and cats in a household. However, it is important to be thorough in the parasite treatment test. Some dermatologists recommend treating cats in the home even if the cats do not have symptoms.
If parasite treatment for scabies is to be done, all contact dogs, symptomatic or not, must be treated appropriately. Ideally, cats should be treated at the same time also because cats can carry the scabies mite and then re-infest the dog(s) after treatment is finished.
There are very safe medications for treatment of scabies, though some medications are not advisable for certain breeds. The choice of therapies would need to be discussed with your veterinarian. Treatment includes specific antiparasite drugs such as ivermectin (oral or injectable), doramectin (oral or injectable), selamectin (topical), moxidectin (topical), lime-sulfur solution (topical), fipronil spray (topical). Multiple doses/applications are needed with treatment period of at least one month. My preference is to use ivermectin in those breeds that tolerate this medication (non-herding/non-MDR-1 mutant breeds).
Besides failing to treat contact pets, the other pitfall of treating scabies is inadequate duration of treatment – it is important not to stop anti-parasite treatments too soon before all mites are eradicated on all pets. Treatment of the indoor environment is likely not necessary if all contact pets are being treated and avoids using insecticides in the home environment. Scabies mites are obligate parasites and do not live very long off of a host animal.
For the very pruritic pet, some symptomatic therapy for the allergic reaction to the mites is indicated to give the pet some quick relief. This is a situation where the benefits of steroid therapy likely outweigh the risks.
Any humans with skin problems should be evaluated by a physician. Humans can get scabies from dogs, though likely not as easily as they can get scabies from other humans.
Cats and mange:
Although there are rare reports of finding Sarcoptes mites cats, it is believed that Sarcoptes mites are not able to live or complete their life cycle on cats. However, cats have a type of mange caused by a species of mite that is related to canine Sarcoptes. This is mange caused by Notoedres mites. These mites cause intense itchiness (pruritus) usually around the head of cats (perhaps because the cat cannot groom its head as effectively as the rest of its body). The diagnosis of Notoedres in cats is similar to the diagnosis of Sarcoptes in dogs. Notoedres can be treated with some of the similar therapies as is used for dogs. Discuss safe options with your veterinarian.
See also... Pet Skin Disease Info