Ectoparasites: Fleas

The most common external parasite of the dog and cat is the flea. Fleas love warm, humid environments and do not survive for long periods in extreme heat, cold, or low humidity. Depending on where you live, fleas can definitely be a year-round concern, though we tend to have heightened awareness during warmer weather. Fleas are wingless insects and cannot fly, but they are capable of jumping as high as 2 feet. Adult fleas feed exclusively on the blood of the host animal.

How do you know if your pet has a flea problem? He might be scratching and have inflamed skin because flea saliva contains components that cause irritation and inflammation. You may see adult fleas on your pet or in the environment, or you might see something called flea dirt. Flea dirt looks like comma-shaped flecks of dirt and is actually the flea fecal matter that contains ingested blood. If you see something that resembles flea dirt on your pet and want to confirm what it is, you can place it on a moist cotton ball or piece of paper. If it is flea dirt, it will turn reddish-brown because of the blood it contains. Some pets can also have an allergic reaction to flea saliva, which can cause a serious condition known as flea bite hypersensitivity. Affected pets may have extremely itchy, red skin, hair loss, or other skin lesions.

Animals with a flea infestation may also have a tapeworm infection because fleas are an intermediate host in the life cycle of some species of tapeworm and are commonly swallowed during grooming. (In these cases, be advised that eliminating the fleas will not eliminate the tapeworms.) Animals that are severely infested with fleas may also develop anemia; typically this is observed in puppies and kittens.

The most important thing to keep in mind when protecting our pets from fleas is that we are not dealing with just the adult flea but the entire life cycle, which has several stages. In fact, it’s estimated that only 1% of the flea population is in the adult stage at any given time. The majority of fleas are in the egg, larval, or pupal stages, and these stages cannot be ignored if we are going to keep our pets flea-free. The adult flea spends virtually its entire life on its host, where the female adult lays her eggs. These eggs fall off the host into the environment, where they develop into mobile larvae and feed off organic debris. The larvae develop into pupae that are highly resistant to cleaning and chemicals and are encapsulated in tough, sticky cocoons. When they hatch into adults, they can leap onto an unsuspecting host, and the cycle continues.

With all of these stages of the flea’s life cycle in the environment, it used to be that we would have to treat the pet and the environment separately with multiple products. Now there are several convenient topical products that eliminate this need. These products are applied to the skin at the base of the neck and have residual action; the active ingredients get absorbed into the hair shaft and then get slowly released over time throughout the skin. They differ in their method of action, but what these topical products have in common is that they disrupt the flea life cycle by killing or inhibiting one or more of the developmental stages. These effects then get carried over from the animal to the environment when dead fleas, hairs, and skin flakes are shed and carry the active ingredient with them.

Even with the new flea products, it is still a good idea to reduce the number of fleas in the environment by vacuuming carpets and washing pets’ bedding frequently. Also, because flea larvae cannot survive dry environments, a dehumidifier can help control fleas indoors. Outside, reduce the number of fleas by keeping the grass cut short to provide less dark space for light-sensitive larvae to hide. These larvae can easily hitch a ride indoors on the shoes or clothing of family members, making fleas just as much a concern for indoor pets as for those that venture outside.

Amy Fischer, Ph.D. – University of Illinois