By Matthew Kearns, DVM
Flea allergic dermatitis was something that I used to only warn pet owners about in the summertime. However, with warm spells in the fall and winter, as well as the flea’s ability to set up shop in our homes, we really have a year-round problem.
Before we can address the problems fleas cause and how to treat/prevent them, we must understand the life cycle of the flea. The flea has four stages in its lifecycle: egg, larva, pupa, and adult.
An adult female flea can lay up to 2,000 eggs in a lifetime and eggs will usually hatch in one to six days. Once the eggs hatch, a slender, white, segmented flea larva forms; it looks similar to a maggot but, luckily, is too small to see with the naked eye. These larvae are not blood suckers, but rather feed on organic debris in the environment. The organic debris can be outside — leaves, dirt, etc. — or inside — carpet fibers and fibers from furniture or bedding.
After five to 11 days, the larvae will spin a whitish, loosely spun, silk-like cocoon, where they develop into pupae. The pupal stage, because of the outer cocoon, are very resistant to the environment and insecticides. The pupa is usually fully developed at seven to 14 days. However, the pupa can develop into an adult flea as quickly as a few days, or slowly, for many weeks, up to 180 days, depending on environmental conditions.
Once the adult flea emerges from the cocoon, it immediately starts looking for a host — our dogs and cats — for a blood meal. Fleas find hosts via various stimuli: body heat, movement, and exhaled carbon dioxide. Once a host is found, the flea feeds through a long, slender mouthpart called a proboscis. Before feeding, the flea pumps anticoagulant-containing saliva into the wound to prevent the blood from clotting. It is suspected that the anti-coagulant proteins in the saliva may be responsible for what is called Flea Allergic Dermatitis.
Luckily, fleas do not carry many parasites or organisms that cause significant disease in our pets. The most common parasite associated with fleas, in my experience, is tapeworm. This parasite is significant in younger pets but I will usually take tapeworms, seen on the fur, or in the stool, as a clue that there is an undiagnosed flea infestation in adult dogs and cats. More commonly, fleas lead to FAD.
Now, I understand that any dog or cat that has a flea infestation is going to be itchy. However, dogs or cats with FAD will break out with a rash that is much more severe from very few, or even a single, flea bites. More specifically, cut your pet in half — just kidding!
Actually, make an imaginary line dividing your pet into two halves: toward the head, and toward the tail. If the rash is primarily in the half of your pet towards his or her head, it is probably not FAD. If it is toward the tail, which would include the ventral (lower) abdomen, inguinal (groin), base of tail, and back legs, then one should put FAD at the top of the list.
Previously, we had to not only treat our pets with foul smelling, and even dangerous, shampoos, powders and dips, but also many times expose ourselves to noxious chemicals to treat the environment, like “flea bombs.” More recently, we found that although fleas need a host and will bite humans, they cannot live on us. More specifically, by treating our pets, we can treat the entire environment.
Nowadays, there is a large selection of flea preventatives that are much safer and treat the pet specifically. Some of the older products, and still best advertised, are now available over-the-counter. This is a double edged sword — the products are much safer and readily available without a prescription, but these products are ones in which I personally see significant failure and suspect resistance.
If you are seeing a specific rash that resembles FAD, even if you are using flea preventatives, see your veterinarian to not only get relief for your pet, but also to discuss alternative flea preventatives.
Dr. Kearns has been in practice for 16 years.