Clinical Suite: Mites

Overview

Chris Adolph, DVM, MS, Southpark Veterinary Hospital, Broken Arrow, Oklahoma

Skin, otic, and respiratory conditions commonly affect dogs and cats; the prevalence for each is estimated at 15%¹, 21%², and 23%³ respectively. A multitude of etiologies exist (eg, allergic, infectious, parasitic). Because more than one etiology is commonly present in a patient, a thorough diagnostic protocol should be followed to allow detection of parasitic organisms and secondary bacterial or fungal infections. The following are common mites that lead to these conditions in small animals.

Related Article: Clinical Protocol for Ticks

Sarcoptes scabiei (Sarcoptic Mange Mite)

With the exception of cats and guinea pigs, almost all domestic mammals can be infested by S scabiei.⁴ Cats may be infested by Notoedres cati, a mange mite very similar to Sarcoptes. Lesions appear first on thin-haired parts of the body (eg, ear margins, elbows, hocks, inguinal and axillary regions).⁵ A hallmark of sarcoptic mange is intense pruritus; infested animals will self-traumatize  attempting to relieve the itching, which may lead to secondary infections, hair loss, thickened skin, and eventually lichenification. If a dog scratches with a hindlimb when the ear margin is rubbed or scratched, S scabiei should be suspected.¹ Transmission of S Scabiei is by direct contact and is extremely zoonotic.

Demodex spp (Demodectic Mange Mite)

These mites are considered normal fauna of the host hair follicles and sebaceous glands. They are routinely detected in younger patients with localized alopecia and will usually resolve once the patient is mature. However, in genetically predisposed or immunocompromised patients, Demodex spp may become debilitating and even life-threating.⁶ Clinical signs occur in these immunodeficient or genetically predisposed patients.⁷ Pustular demodicosis, characterized by moist, purulent dermatitis with an unpleasant, rancid odor, may develop. The prognosis is poor without proper treatment.

Otodectes cynotis (Ear Mite)

Ear mites are common in dogs, cats, and ferrets worldwide. All developmental stages of Otodectes live deep in the external ear canal.^4,8 Transmission occurs through direct contact with an infected animal; younger patients tend to be more affected. Unlike Sarcoptes and Demodex, ear mites live as surface parasites only, piercing the skin to feed on blood, lymph, and serum. Clinical signs range from asymptomatic to severe otitis externa; debris is typically dark brown to black and thick. Secondary bacterial infection, yeast infection, and aural hematomas may develop as a result of excessive head shaking.

Pneumonyssoides caninum (Nasal Mite)

These mites are commonly referred to as nasal mites because of the infestation site (ie, the nasal sinuses of dogs). Details of the life cycle are not completely understood; however, adults with 4 pairs of legs and larvae with 3 pairs have been identified.⁹ Clinical signs include hyperemia of the nasal mucosa, nasal secretions, tearing of the eyes, chronic sneezing, facial pruritus, and epistaxis.¹⁰

Cheyletiella spp (Fur Mite)

Like ear mites, these mites are nonburrowing and pierce the skin to feed on blood, lymph, and serum.⁴ Although most infested patients are asymptomatic, clinical signs can include mild alopecia, pruritus, and skin scaling that resembles eczema. Fur mites can survive several days off the host, so infested bedding and household furniture may be a source of infection.

Treatment Plan

Chris Adolph, DVM, MS, Southpark Veterinary Hospital, Broken Arrow, Oklahoma

Sarcoptes scabiei

Selamectin, 6–12 mg/kg q30d (label dose¹¹) or q2wk (greater efficacy)

• Labeled for treatment and control of S scabiei.

A moxidectin/imidocloprid combination, flumethrin/imidacloprid collars, and spray-on fipronil are approved for the treatment of sarcoptic mange caused by S scabiei. Other off-label treatments include amitraz, lime sulfur dips, milbemycin oxime, moxidectin, and doramectin. However, nonapproved treatments are rarely necessary.

Demodex spp

Localized lesions

• Amitraz, used spot-on

  • Young dogs with localized lesions will usually recover spontaneously at maturity.¹² Consider the above only if treatment is necessary.

Generalized form

• Amitraz (dogs)

  • Adverse effects can occur, and dipping is labor-intensive.

• Ivermectin, q24h at high doses

  • Exercise caution in dogs susceptible to the MDR-1 gene mutation.

    • Test patients at risk for this gene mutation before treatment.

    • Use caution in dogs receiving spinosad-containing medications, as neurologic side effects have been observed in dogs receiving this combination.¹³

• Milbemycin oxime, q24h

  • Beneficial for dogs that cannot tolerate other treatments.

• Injectable doramectin, q1wk

  • Use caution in MDR-1 susceptible dogs.

• Moxidectin, label dose

  • Used more frequently in an extralabel fashion.  

Treatment is imperative; every attempt should be made to determine and treat the underlying condition. Ovariohysterectomy should be performed on female patients, as demodicosis will recur with estrus. Any secondary pyoderma must be treated with antibiotic therapy; bathing with benzoyl peroxide shampoos is advantageous.

Otodectes cynotis

• Topical milbemycin oxime and ivermectin, single dose applied directly to the affected ear canal(s)

• Systemic miticides (eg, selamectin, moxidectin/imidocloprid), label dose q1mo

  • Effective in treating current infestations and possible re-exposure.

The first treatment goal is thorough cleaning of the affected ear canals. Topical medications will be more efficacious when allowed to reach the infection site.

Pneumonyssoides caninum

There is no approved treatment for nasal mites, but ivermectin, milbemycin oxime, and selamectin have been used.^14,15 Ivermectin should be avoided in breeds with MDR-1 sensitivity.

Cheyletiella spp

These mites are susceptible to all the avermectins mentioned. The key is treating not only all affected household pets with an appropriate avermectin, but also treating the environment with pyrethrins. All clothing and bedding should be washed thoroughly, the household vacuumed, and all in-contact hosts treated.

Physical Examination

The veterinarian should determine:

• If lesions are generalized or localized, and to what area and extent

• If the lesion is pruritic or nonpruritic

• Presence of secondary conditions

• Presence of otitis externa and character of the debris

• Presence of sneezing and visibility of mites on the external nares.

Key diagnostics include:

• Skin scraping of affected areas to rule in/out Sarcoptes scabiei, Demodex spp, Notoedres cati, and Cheyletiella spp  

• Otic cytology to reveal possible Otodectes cynotisor or identify secondary bacterial and/or yeast infection

• Skin surface cytology to identify Cheyletiella spp and secondary bacterial and/or yeast infection

• Rhinoscopy to diagnose nasal mites.

Team Roles

Chris Adolph, DVM, MS, Southpark Veterinary Hospital, Broken Arrow, Oklahoma

The following outlines roles and responsibilities of each team member when managing mite infestation.

Team Training Plan

Nan Lillard, MA (Organizational Management), University of Tennessee

The veterinary team plays an important role in providing effective and successful mite treatment. Determining how each team member can support the treatment plan is key to your team’s effectiveness and, ultimately, success. Training should be reviewed with the entire team periodically.

Basic Training

This is an opportunity for the practice manager to team with the veterinarian to provide training and clarify every team member’s role, and for the team to review educational materials (eg, handouts, websites) to ensure they are current and accurate.

Training should include information about effective client communication regarding mite infestation and treatments, human and animal risks, and clients’ financial concerns. It should also include a presentation from a veterinarian on the common types of mites and potential infestation sites, typical treatments, and follow-up care. Use role-play activities to practice asking clients open-ended questions to assess observations and behavior that may indicate a patient’s possible mite infection.

Suggested content for the practice manager’s presentation:

• Challenges when communicating with clients who may not comply with recommended treatment plans

• Communicating with clients concerned about the cost of care

• Educating clients about at-home care

• Policy and procedures for following-up with clients after a mite infestation diagnosis.

Suggested content for the veterinarian’s presentation:

• At-home care and preventive options

• Diagnosis and treatment of mite infestation

• Mite transmission (if transmission is possible)

• Signs of primary infestation and potential secondary infections

• Types of mites and potential infestation sites

• Typical treatments and associated costs

• Zoonotic concerns.

Communication Keys

Nan Lillard, MA (Organizational Management), University of Tennessee

The client should be recognized as an important member of the healthcare team because he or she can provide valuable and important information about the patient’s behavior that may lead the veterinary team to assess the patient for mite infestation.

Examining the patient for signs of mite infestation and taking a thorough history from the client is an important component of routine healthcare. It is important to educate the client about mite-infestation signs, potential effects to the patient, the possibility of the patient passing the infestation to the client or other family members (ie, zoonosis), the importance of preventive care, and what to do if he or she suspects a pet has mites.

Be sure to communicate the following to the client:

• Patients should have regular health examinations, as their health may change in a short period of time.

• Mites can be extremely irritating to patients and can cause serious skin problems or carry disease.

• The client should look for coat or skin abnormalities (eg, hair loss, flaking skin, small pustules, crusting).

• The client should watch for behavior signs such as head shaking and excessive scratching, as scratching until the skin is raw or bleeding may signal mite or other parasitic infestation.

• The client should consult a veterinarian if any signs or behaviors indicate possible parasitic infestation.

Support the client by:

• Being prepared to answer questions about mite infestation and the effects on the patient’s health and quality of life (see the client handout Mite FAQs & Common Misconceptions)

• Being prepared to answer questions about possible zoonotic infestation; document this conversation in the patient’s medical record

• Providing information about necessary cleaning or fogging agents or products, along with instructions on how to clean the home and kennel

• Inviting the client to ask questions.