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Medical Corner:
What's Bugging Your Rats and Mice?


Jan McArthur, RVT
From the March/April 1999 Rat & Mouse Gazette

Ecto-parasites are the external parasites that infect all living creatures. Those that infect rats and mice most commonly include lice and mites. Sometimes, even though it is less common, we see infestations of fleas, flies, or ticks, but since the main ones to affect our pets are lice and mites, this article is only about those nasty critters. Once your pets are infected by external parasites, it can be difficult to treat them successfully, but it isnít impossible. It is important to understand the life cycle of parasites in order to successfully treat your pets and keep those pesky bugs off of them.


WHAT IS THE DIFFERENCE?


Taxonomy is the system to establish the hierarchy and classification of a given group of organisms. Mites and ticks are classified as arachnids; lice and fleas as insects. The lice are further classified into groups of blood sucking (Anoplura) and the non-blood sucking, biting lice (Mallophaga). Mites can cause mange in rodents just as they can in dogs. Lice, and some mites, can be seen without a microscope, but other mites need to be diagnosed by a vet using the skin scraping method and a microscope.


LICE ARE NICE


Keeping that little phrase in mind helps you to remember that lice are species specific. Infestation by lice is called pediculosis. Although rats and mice may both be infected with lice, those lice will not cross over from one species of animal to another. The lice of rats and mice are the same genus, but they are not the same species. Rat lice are Polyplax spinulosa and mouse lice are Polyplax serrata. If a mouse louse jumps onto a rat, it wonít take long for it to realize this rat is not its food source and will jump off to find a mouse, and vise versa. This also means you will not catch lice from your pets, and if you were infected with head lice, you could not transfer them to your pets. Transmission from mouse to mouse or rat to rat is by direct contact and by fomites (objects).

Both the mouse and rat lice are Anoplura (bloodsuckers), making it vital to your pet that you rid them of these pests as quickly as possible. These can cause anemia, but even more importantly for rats, they may transmit the blood parasite Hemobartonella muris, which is a rickettsial blood parasite similar to tick fever. They may also transmit Rickettsia typhi between rats. The Ricketsia typhi (not typhoid fever, but much like tick fever) may be passed to humans via rat fleas. These blood parasites can be more deadly to your pet than the lice.


MITES ARE NOT SO NICE


Mites are different than lice because they are not species specific. However, they are generally host specific, meaning they will usually attack only a certain species host, but they will sometimes cross over from one species to another. They will do this if their choice of host is not available. Infestation by mites is called acariasis. There are three categories of mites that infect mice and rats: fur mites, burrowing mites, and the most serious, bloodsucking mites.


MOUSE MITES


The three most common mites of mice are the fur mites, Myobia musculi, Myocoptes musculinus, and Radfordia affinis. These are not bloodsuckers and are often endemic to mice populations with no visible symptoms. Transmission between mice is by direct contact. These mites are not known to infect humans. These mites wonít cause harm to the mouse unless the infestation is heavy, or unless the mouseís immune system is in some other way compromised. Symptoms you may see are patches of hair loss or skin lesions and ulcerations. That sounds as if itís not so bad for mice, however, mice donít get off so easily because rat mites may also attack them and cause severe problems.


RAT MITES


Rats may be infected with three types of mites. Radfordia ensifera, the fur mite of rats, is very similar to the fur mites of mice. They wonít cause problems unless the infestation is heavy or the rat is ill with another disease. Symptoms will be the same as those of mice, patches of hair loss with possible skin ulceration or lesions. These also are not known to infect humans.

Burrowing mites of rats are Notoedres muris. These are the ear mange mites. A skin scraping and a microscope are needed to see these mites. They attack the ear pinnae, tail, nose, and extremities. Lesions caused by this mite are reddened, crusty, itchy areas. These mites are spread by direct contact, so it is important that you keep wild mice and rats away from your pets. They may also infect other rodents, but are not known to infect humans.

The bloodsucking mites that infect rats and may also infect mice are Ornithonyssus bacoti. They are the most dangerous to your pets. This one is closely related to ticks and is especially common in tropical and subtropical areas. This is the one that will feed on rodent blood, then drop off to hide in wood products, cracks, and crevices in or near the cage. O. bacoti will cause anemia, and, like the lice, it will also transmit rickettsial blood parasites. These may be seen without a microscope in the bedding or in and around the cage. This mite has a wide range of hosts that includes other rodents, and this one will attack humans. It is transmitted by direct contact with an infected animal, but also may arrive in contaminated bedding or wood products. Be careful not to buy open bags of bedding for this reason. Freezing your bedding before using may help eradicate these mites.


WHAT TO DO ABOUT EXTERNAL PARASITES


The life cycles of external parasites are fairly simple as compared to internal parasites. In order to rid your pets of external parasites you need to understand their life cycles. The adults are easily killed, but the eggs are left behind and will hatch after the first treatment. Mites are arachnids, so they have eight legs. In the mite, life cycle stage one is the egg, or nit, which hatches to stage two, the six-legged nymph (larvae). In stage three, they molt into the eight-legged nymph, and then into the final stage, the adult. It may take only a week for the mites to complete the life cycle.You have to hit them when in the nymph or adult stage of life. This is why itís so important to disinfect your cage at least once a week, and, anything in it, as well as treat your pets more than one time to kill all the parasites. Disinfecting with bleach is the fastest and easiest way to kill any type of microorganisms in the cage, including bacteria, virus, or fungi. Throw away anything made of wood as the eggs or nits may be hidden in it, and wood is not easily disinfected.

Insects such as lice are six legged creatures. Lice spend their entire life cycle on the host in just three stages: egg, nymph, adult. Their life cycle may be as long as 14-21 days. They lay their sticky eggs (nits) on the hairshaft so you can actually see them. This is where the phrase ďnit pickingĒ comes from; you can actually pick them out of the fur yourself.

The life cycle will determine how often you treat, but the type of treatment is also a factor. There are several ways to treat: oral, injectable, and topical. Each type of treatment has its advantages and disadvantages. Itís best to see your vet to get a diagnosis before initiating any treatment, although treatment for most of these creatures is the same.

Ivermectin, dosed orally or as an injectable, is often used safely in rodents, but it is not the be-all, end-all answer to parasite problems. You must still disinfect the cage and everything in it, or you will never stop the problem. Be aware that Ivermectin is a drug, and while it is relatively safe, as with any drug, the possibility exists that it can have adverse reactions in certain individual pets sensitive or allergic to it.

Topical treatments are sometimes safe, but they, too, can cause adverse reactions, and often are not very effective. There are powders, dips, foams, sprays, shampoos, insecticide strips, and guards on the market. Many of these are not at all safe for rodents. The dog and cat flea powders are not safe, they are too powerful and can poison your rat or mouse. The insecticide strips and mite guards for birds also are not safe. Rodents may eat them through the bars of the cage, or the odor from them may expedite respiratory problems, forcing them to be placed so far away from the mice and rats that they are not effective.

Dips, foams, sprays, and shampoos with the active ingredient pyrethrins, at no higher than 0.15%, are fairly safe, and some of them are effective. Pyrethrins are a natural substance that is extracted from chrysanthemum flowers. However, just because it is a natural substance does not mean it cannot be toxic to rodents. If a product is safe for two-week-old kittens, it is probably safe for rodents, but you should check with your vet before using one.

If your rats or mice are miserable, itchy, and developing lesions, think about these nasty bugs, but have no fear because you can get rid of them!


Ed. Note: For more information including Sarcoptes Scabiei, please refer to the Rat Guide article on Ecto-Parasites.