Managing Sarcoptes Infestation in Dogs

Veterinary nurses play a significant role in the identification, diagnosis, and treatment of Sarcoptes infestation, often called “sarcoptic mange” or “scabies,” in dogs. The most important goal is to identify potential cases. By understanding differentiating clinical signs and obtaining a thorough history, veterinary nurses may even prevent other patients from becoming infested by identifying cases before they enter the hospital, thereby avoiding cross-contamination.

An itchy patient is one of the most common reasons an owner schedules an appointment with their pet’s veterinarian. The goal of the veterinary medical team is to determine the primary cause of pruritus and address any secondary infection.

The Pests and Parasites series is brought to you by Merck Animal Health, the makers of Bravecto® (fluralaner) and Sentinel® (milbemycin oxime/lufenuron).

Canine infestation by Sarcoptes is caused by the mite Sarcoptes scabiei (FIGURE 1) and should always be on the list of differentials for a pruritic patient. S scabiei infestation often mimics other inflammatory skin diseases, including atopic dermatitis, food allergies, contact reactions, and pemphigus foliaceus, as well as other parasitic infestations.

Figure 1. Sarcoptes scabiei mite. Yonlada Rithitham/shutterstock.com

Despite the similarities between these conditions, there are a few distinct characteristics of scabies that veterinary nurses should be aware of:

• Infestation of S scabiei often presents as a sudden onset of marked, progressive pruritus.
• Scabies also tends to first affect areas of the elbows, hocks, tips of the pinnae, and ventrum because the mites prefer areas of skin with less hair.

A veterinary nurse’s daily role often includes obtaining a complete medical history for each patient that enters the hospital. A complete dermatologic history should include:

• Approximate date of onset of pruritus
• Current level of pruritus on a scale of 0 to 10
• Previous treatments administered
• Patient’s response to those therapies

It is also helpful to note whether or not the patient has housemates or humans in the household exhibiting similar signs and whether the patient has been in contact with other canids.

It is important for the veterinary team to consider infestation by Sarcoptes as a diagnosis for a chronically allergic patient whose allergies are typically well managed but suddenly has developed intense pruritus with concurrent secondary pyoderma. Ruling out scabies as a contributing factor with an appropriate treatment trial may be warranted.

Scabies Life Cycle

The complete life cycle of a S scabiei mite takes approximately 17 to 21 days. Once an animal is infested by an adult mite, the mites begin to mate in molting pockets in the top layers of the patient’s skin. Female mites then burrow through the skin and lay their eggs (ova). The eggs hatch into 6-legged larvae that travel back to the surface of the skin to begin feeding.¹ When identified microscopically, adult S scabiei mites appear round or oval shaped with a terminal anus. They have 4 pairs of short legs and are approximately 200 to 400 µm in length.²

Signalment, Signs, and Sources of Scabies Infestation

There is no breed or sex predilection for canine scabies. Classic clinical signs include alopecia, crusting, and papular erythema. If present for an extended period, scabies may cause generalized dermatitis and intense pruritus (FIGURE 2). Contact with other canids, including foxes and coyotes, or visits to dog parks, groomers, and even veterinary hospitals may be the source of the infestation.

Figure 2A. A 4-year-old neutered male Labrador retriever infested with Sarcoptes scabiei.

Figure 2B. Patient was presented with progressive pruritus and dermatitis affecting its ventrum, distal limbs, both pinnae, hocks, and elbows.

Figure 2C. Patient was not on any medications, including parasite preventives.

Figure 2D. A housemate’s exam was within normal limits; however, the owner noted mild pruritus starting over the previous 3 weeks.

Diagnosis of Scabies

Confirmation of infestation by Sarcoptes is made by identification of the mite, fecal pellets, or ova.² A diagnostic skin scrape is best achieved by performing long strokes against the skin, collecting any crusts or debris, and adding it to the slide. Achieving capillary bleeding is not necessary because the mites live in the top layers of the skin. For detailed instructions on performing a skin scrape, visit theveterinarynurse.com/review/article/how-to-perform-a-skin-scrape.

Just a few mites can cause intense pruritus, and mites are often difficult to obtain on skin scrapings due to the mites’ burrowing nature; thus, a negative skin scrape does not rule out Sarcoptes infestation. A diagnosis may also be obtained by using an appropriate antiparasitic treatment and monitoring for full resolution of clinical signs.

A positive pinnal-pedal reflex is another distinct feature of dogs with scabies. While the examiner scratches the apex of the pinnae, the patient may bring its hind limb up in a scratching motion. This test has been reported to have a sensitivity of approximately 80% and a specificity of approximately 93%.³

Treatment and Prevention of Scabies

Overall, several treatment options, including some newer ones, are available for sarcoptic mange. Historically, topical therapies that were often labor intensive and time consuming for owners were required to eradicate the Sarcoptes mite. Today, there is 1 U.S. Food and Drug Administration–approved option: Selamectin applied every 30 days is effective against scabies. There is some evidence that a more frequent application of every 14 days (off label) is more effective at killing the mites, thus making patients more comfortable more quickly.¹

The drug class of isoxazolines (fluralaner, afoxolaner, sarolaner) is not approved for treatment of Sarcoptes in the United States; however, many recent studies have proven it effective, with a significant decrease in dermatitis and pruritus after 14 days and full resolution of clinical signs in 21 to 28 days.^3,4 Some evidence shows that there may be an increase in pruritus following the antiparasitic application due to the mites dying under the skin; owners should be made aware that pets may get worse before they get better.²

For a successful treatment outcome, any secondary pyoderma must be addressed with a full 4 weeks’ duration of antibiotics, and all animals that come in contact with the patient receiving treatment should be appropriately treated to avoid reinfestation. Following treatment of the patient, extensive cleaning measures of the home are not necessary beyond washing bedding and disinfecting hard surfaces. Although mites can live off (without) a host for an extended time depending on the environment, they only remain infectious for approximately 36 hours once a host has been treated.¹

Feline Scabies

Feline scabies (notoedric mange) is caused by Notoedres cati; it is less common than S scabiei infestation in dogs but also highly contagious. Feline scabies mostly affects cats but may also affect dogs, foxes, and rabbits. The life cycle of N cati is closely related to that of S scabiei. Microscopically, N cati mites are slightly smaller, with terminal suckers and a dorsally located anus.²

Clinical signs for notoedric mange do differ slightly and include marked lichenification (skin thickening, hyperpigmentation, and exaggerated skin folds) and thick, adherent crusting (FIGURE A). Secondary alopecia and excoriations are often present. Like canine scabies, notoedric mange is extremely pruritic, and differential diagnoses include other parasitic infestations, atopic dermatitis, food allergy, and pemphigus foliaceus.

Figure A. Cat with clinical signs of sarcoptic mange infection from Notoedres cati mites. Suharji Esha/shutterstock.com

Treatment options for feline scabies are also similar to those for canine scabies; however, extreme caution should be taken with many antiparasitic agents due to the high levels of possible toxicity to feline patients. Lime sulfur dips have been proven to eradicate the mite, but thorough client education is necessary to ensure correct dilution and application of the product.¹ Other effective treatment options include the isoxazolines sarolaner (Simparica; Zoetis, zoetisus.com) and fluralaner (Bravecto; Merck, bravecto.com), which have been shown to be efficacious in recent studies. Treating all in-contact cats will ensure successful eradication of the mite.⁵

Client Education and Zoonosis

Educating clients on the zoonotic potential of scabies is another integral part the veterinary nurse will play once a diagnosis has been made. It is important to mention to pet owners that despite the scabies mite mostly infesting canids, humans may also be transiently affected. Human infestation is usually self-limiting; however, a heavy burden within the home or prolonged close contact with an infested patient may increase the likelihood of humans becoming affected. Young children and people with a decreased immune status may experience a lengthened course of infestation. Affected humans typically present with extreme pruritus and papular erythema, most commonly along the beltline. If a client is concerned that they may also be infested, a visit to their dermatologist may be warranted to ensure they receive proper diagnosis and treatment.

Summary

Veterinary nurses play a large role throughout the veterinary hospital each day and can be a great aid in all dermatologic cases. Because many parasitic cases mimic allergies, careful consideration of patient history and clinical signs are vital to helping the veterinarian make a correct diagnosis. Skin scrapings and cytology samples are always needed and will also help with diagnosing any secondary pyoderma that may be present. New and old antiparasitic medications have simplified scabies prevention and treatment and have made it easy to confirm or rule out the mite as a cause of intense pruritus. While scabies might seem like a difficult diagnosis to make, the medical team can turn an infested patient with intense pruritus into a happy, healthy patient.