Mites: Can we scratch that itch?

by John Maniatty, DVM

Your puppy or kitten constantly scratches and licks; they cannot get relief. Their skin is crusty, and they are losing clumps of fur. You bathe them, but it is not helping. It doesn’t appear to be fleas, and you have given them Benadryl, still with little relief. What is causing all itchiness? Could it be Mites?

Mites are microscopic arachnids of the skin. Some live on top of the skin, like those of the family Trombiculidae (Chiggers) and Otodectes Cyonitis (Ear Mites). Others live just below the skin, like Cheyletiella (Walking Dandruff), Sarcoptes scabiei (Scabies), and Demodex species mites (Mange). Demodex are normal skin inhabitants, while all the rest come from outside sources. Mites generally do not live long off the host body but can be transferred from animal to animal/human and plants, bedding, and soil. Mites feed on the material in the skin and the skin cells themselves. The digestive juices they use to break down the cells and other materials in the skin lead to inflammation. The mites also tunnel into the skin and lay eggs, creating inflammation and can lead to allergic reactions. Clinical Symptoms you may see because of this are pruritus (itching), licking, chewing, skin sores, crusts/dandruff, and alopecia (hair loss).

A skin scraping, acetate tape preparation, hair plucking, skin biopsy, and treatment response can determine a mites diagnosis. Skin scraping requires using a scalpel blade to scrape the skin deep enough to make capillary bleeding. The sample is then examined on a microscope slide. Unfortunately, mites or eggs are only seen 50 % of the time with this technique.

For the acetate tape preparation, one takes the clear scotch tape and touches it to the skin at areas of sores and irritation. It is then transferred to a microscope slide. Only 50 % of the time will you see mites or eggs. One of the benefits of the acetate tape test is that it allows for staining of the tape prep and looking for secondary bacterial or yeast infections.

A biopsy is much more sensitive, and if mites are present, they will be seen at a higher percentage than the previous techniques. It also can be used to diagnose other possible causes. The significant drawbacks are that it is much more traumatic and expensive.

Hair plucking is used for Demodex identification because they live in the hair follicles and sebaceous glands/blackheads.

In some cases, treatment response and patient history are all we can use to diagnose mites. We do this sometimes when we are highly suspicious of mites and the less sensitive tests return negative.

A mite’s ability to infest other animals varies from mite to mite. Chiggers are rare in dogs and cats but are more common in humans. The eggs are in the soil or decayed plant/wood, and the larval stages are mites when they hatch. The mites crawl on the skin and place digestive enzymes down to dissolve the skin to ingest and make tunnels to crawl in the skin. Next, inflammation occurs, which can be seen in the form of sores, nodules, wheels, and plaques.

Ear Mites live in the ears and on the head. They are species-specific to dogs and cats; they do not infect humans. They lay eggs in the ear that hatch and are asexual when hatched. The asexual mite binds to the male mites and develops into male or female. Males disconnect. Females stay connected and copulate with males and lay their eggs. There is a 4-day incubation period. Once hatched, they feed on the skin cells and waxy debris. They do not live long off the body. Their life span is about 21 days.

Cheyletiella, commonly called Walking Dandruff, are not host-specific mites. Dogs, cats, humans, and rabbits are prone. Different species of these mites are more prominent in dogs versus cats versus rabbits, but all can infest each other and humans. They do not always cause a reaction; if not, the more common species may be temporary. They are transmitted by contact with the infected animal or from fomites such as plants, bedding, and cages. Unlike many other mites, they can live off the host for 21-30 days. In addition, these mites can lay eggs in the environment leading to sources for re-infestation.

Sarcoptic mites (Mange) tend to be somewhat species-specific in that the specific host can be infested, and the mites can continue to propagate for a long time, while with other mite species, it can be transient (short-lived) or not at all. Mites are passed through direct contact and fomites. Their life span is roughly 21 days.

Demodex are normal inhabitants of the skin. However, they overgrow in young puppies and kittens whose immune systems are immature and not strong enough to keep the mites in check. It is also seen in immune-compromised older pets. In this case, further workup may be needed to determine what led to the weakened immune system. Their life span is from 20-35 days.