Sarcoptic mange, aka “Scabies,” is a parasitic dermatosis caused by mites living on and burrowed within the skin of the host animal. Although these mites exhibit a host preference, they have zoonotic potential for causing skin problems in humans. Sarcoptic mange may be the cause of severe itch in dogs and may be cured with effective treatment.
Scabies (sarcoptic mange) causes a non-seasonal intensely pruritic (itchy) popular and crusting dermatitis in dogs and is caused by the epidermal mite Sarcoptes scabiei var. canis. Although scabies mites live in the superficial layers of skin, the mite’s antigen can reach the lower layers of the skin and induce immune responses. Dogs may develop protective immunity after infestation. Although the mite is susceptible to high temperatures and drying, it can live in the environment for up to 21 days under ideal environmental conditions. Scabies is highly contagious and is primarily transmitted by direct contact with an infested animal. Fomite and fur transmission to humans or other animals via contact with grooming equipment or at kennels can occur. Cats may be reservoirs for these mites, but do not usually need to be treated.
The body sites typically affected in the dog include the ear pinnae margins, elbows, hocks, and the ventral chest. Lesions and pruritus can become widespread, but the dorsum/top of back is usually spared. Early lesions are characterized by erythematous papular eruptions (red bumps) that develop thick yellowish crusts. With time, self-excoriation results in patchy to widespread alopecia, and generalized papulocrustous dermatitis. Hyperpigmentation (greying of skin) and lichenification (thickening of skin) are the most dominant lesions with chronicity. Some dogs are intensely itchy, but have few lesions other than mild erythema and occasional excoriations. Others may have mild pruritus, yet have an abundance of mites. This is called “Norwegian” scabies.
The diagnosis of scabies is based upon 1) a history of rapid onset of intense pruritus and progression of lesions, 2) having a likely source of infestation from visits to training or boarding facilities, dog shows, dog parks, grooming parlors, etc., 3) recognizing a potential exposure of the dog to other species known to harbor the mite, e.g. coyote or fox, 4) and having another in contact animal or human develop itch and rash. The absence of itch among in-contact animals or their humans does not rule out scabies. To make a definitive diagnosis, one must demonstrate the presence of a life stage of the mite. Superficial skin scrapings are the common diagnostic test. The mite is very difficult to find. Failure to find it does not rule out scabies. Trial therapy is often used if the degree of suspicion is high enough to justify empiric treatment.
A number of products are effective for treatment of sarcoptic mange. Many have potential for toxicity and adverse reactions in certain breeds or species. Idiosyncratic reactions have even been reported in certain breeds at therapeutic doses. Use of a product approved and licensed by the United States Federal Drug Administration (FDA) for the target animal species and disease being treated must be attempted first. Any other application is extra-label usage of that drug. The FDA recognizes the need for extra-label usage in veterinary medicine, but informed consent should be obtained. If the FDA product cannot be used in a particular animal, one may use a drug that is approved for another disease in the species being treated. All dogs in contact with the affected animal should be treated. Affected and in-contact animals should not socialize with other dogs or travel where there may be fur-bearing animals. Heartworm testing is recommended prior to treatment. If a therapeutic trial does not result in the reduction and subsequent resolution of clinical signs within 3-4 weeks, the animal should be reassessed by a veterinarian for other causes of itch.
- Ivermectin(Ivomec; Merial Animal Health) and Selamectin (Revolution; Zoetis) are the most commonly used in the northeastern USA. Selamectin is apparently safe in collies, related breeds, and their crosses.
- 0.25% fipronil spray (Frontline Spray; Merial Animal Health) may be used in very young animals or if other products are contraindicated. Use of this spray would be extra label.
- Dips may be indicated in certain situations. Lime sulfur is the safest dip for young animals or otherwise sick patients. Amitraz (Mitaban; Pfizer Animal Health), is another dip that is effective, but its use would be extra label. The authors recommend the dip be performed by trained personnel in-hospital where the dog can be monitored for side effects for several hours after application. Owners should be informed of side effects and signs to monitor for at home after application. Yohimbine and atipamezole are antidotes.
Mites die after a few days when off the host, but general clean up of the environment and application of a parasiticide containing permethrin may be beneficial when a number of animals are affected (e.g., a kennel or pet shop). Environmental treatment may prevent reinfestation from point sources.