What A Pest

Every pet specialty retailer that sells small animal products should know how to identify and treat common external parasites.


External parasites are common in many small animals, but each species has to deal with different parasites. In rabbits, for example, the most common parasite is the ear mite, but rabbits can also be prone to fur mites and fleas. Guinea pigs commonly have fur mites and can, in rare occasions, suffer from mange mites, which can cause fur loss, skin damage and debilitation. Ferrets typically have problems with fleas, and sometimes with ear mites. The most common ectoparasite in hamsters is a demodex mange mite, but it rarely causes symptoms. The most common parasites in mice are mites, and rats commonly suffer from fur mites and lice. External parasites are not common in gerbils and chinchillas, probably because the dust they bathe in helps to prevent them.

Most of these parasites only attack their host, but there is one, the tropical rat mite, that will bite anything and anyone, including humans. The adults are smaller than a pinhead and the larva are microscopic. Because this pest lives in the environment and only crawls on its host to feed, treating the animals is not enoug–the surrounding area must be cleaned and treated with a pesticide too. Fortunately, this pest is rare.

Topical Products
Topical products to control external parasites come in the form of sprays, powders, shampoos and dips. The active ingredient in most of these products is pyrethrin. This is a naturally occurring chemical that is produced from the chrysanthemum plant. There is also a stronger synthetic pesticide called permethrin. Products with permethrin should not be used on small animals; they are usually labeled only for dogs. 

Pyrethrin is generally effective for external parasites that live on top of the skin. This includes fleas, lice, ticks and some types of mites. It is effective against tropical rat mites. Mange mites that burrow into the skin are protected by the skin and will not be killed by a topical pyrethrin product. The rat fur mite also does not seem to be eliminated with topical treatment; perhaps the larvae are small enough to hide inside the hair follicles.

Some pyrethrin products are specifically labeled for use on small mammals. These are usually sprays. There are also products designed to be put into the ear to combat ear mites in ferrets and rabbits. When used according to label directions, these pyrethrin products are safe for use on most small pets. Occasionally, an individual can have a bad reaction and might become weak or wobbly, and sometimes they will drool. In this case, pet owners should immediately bathe the pet with a mild soap to remove the pesticide.

Systemic Treatments

Spot-on and oral products are gaining popularity. Oral products are absorbed into the bloodstream and then delivered to the parasite when it sucks the animal’s blood. Some oral products are designed to kill the parasites outright; others are insect growth regulators that prevent fleas or lice from developing. Growth-regulators do not work for mites. Mites and ticks are arachnids, not insects, so only products that work for ticks will work for mites. Of the spot-on products, only ivermectin, selemectin and fipronil will kill most mites. Ivermectin, an over-the-counter product, can also be given orally.

Spot-on products come in two types. In one type, the active ingredient stays on the skin, spreading across the body through the natural skin oils, and is not absorbed into the body, so it really isn’t a systemic treatment. The other type is absorbed into the blood and then reappears in the skin oils.

Most spot-on and oral products are labeled and marketed only for dogs and cats, but they can often be used for small pets. When a spot-on product is applied to a small animal, the pet should be separated from other animals and distracted with a treat or human attention to prevent grooming until the product dries. Once the spot-on liquid is dry, the animal will no longer be able to lick off a significant amount.

Tough Cases
Pyrethrin products can be used on small animals to treat most ectoparasites. However, mange mites in guinea pigs and fur mites in rats must be treated with an alternative product. Guinea pigs with mange mites usually have hair loss and rough skin with sores, and will typically need to be taken to a veterinarian. The symptoms of rat fur mites, which are extremely common, are usually not so dramatic, often just some scabs around the rat’s neck. 

Ivermectin used to work for rat fur mites, but now the mites have developed a resistance to it. I recommend selemectin for treating fur mites in rats. Selemectin is sold through veterinarians only. However, since they are the only products that will work in certain circumstances, retailers must know when to recommend them and when to sell customers a product off their shelves.

Debbie Ducommun has a B.A. in animal behavior and has worked in the animal field since 1982. She is the author of Rats!, the booklet Rat Health Care, and The Complete Guide to Rat Training: Tricks and Games for Rat Fun and Fitness.

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