With flea season in full swing, we wanted to offer some advice for pet parents who may be dealing with itchy dogs and cats. Below, read a helpful article written by VCA SFVS’s own Karen Truong, DVM, and Carlo Vitale, DVM, DACVD. Learn more about our dermatology and allergy department.
Fleas and Flea Allergy
– By Karen Truong, DVM, and Carlo Vitale, DVM, DACVD, VCA San Francisco Veterinary Specialists
My dog has been chewing obsessively at himself. His tail is naked, and his underside is red and raw. My veterinarian thinks he is allergic to fleas. I use medication for fleas through the spring and summer whenever fleas are around, and I never see fleas on him. What is flea allergy, and how do I treat it?
Flea allergy dermatitis (FAD) is the most common skin disease of dogs and cats and is caused by an allergic reaction to flea bites. FAD occurs worldwide, affecting dogs and cats of any age, breed or sex. Just one flea is enough to cause FAD.
FAD is characterized by itchiness:
- In dogs, biting, chewing and licking are mainly observed at the rear half of the body, especially near the tail base and inner thigh. This obsessive behavior can result in hair loss, redness, hot spots and secondary skin infections.
- Flea allergy in the cat can be slightly more subtle. A cat may present with just hair loss on the back half of the body, especially inner and back thigh, without obvious redness caused by over-grooming. Some cats have tiny bumps around the neck and/or base of rump.
With FAD, you may observe waxing and waning itchiness that may correspond with flea season, although with the moderate weather we enjoy in the Bay Area, licking and chewing may be observed year-round. Occasionally, a flare-up may be associated with a new pet in the household, a recent visit to a boarding or grooming facility, or discontinuation of regular flea control, or just before flea medication is due. Rarely do we find an infestation of the pet or home.
Treating FAD requires:
- Complete flea eradication
- Symptomatic relief to the pet
- Prevention of future infestation
Warning: This next section may make your own skin crawl! Adult fleas begin to feed within a few minutes after hatching. They remain on their host for the entirety of their adult life. They begin to breed on the pet within a day or two. Female fleas are capable of laying up to 50 eggs per day. The eggs fall to the ground and hatch into larvae. Larvae can live in soil, grass, carpets, pet bedding, furniture and cracks between hardwood floors. Mature larvae will transform into a pupae with a protective cocoon. Approximately one week later, the newly emerged adult is ready to leap onto the host to begin the cycle again.
All stages of the flea lifecycle can survive temperatures as low as 28°F, and as high as 95°F. In colder climates, fleas may continue to survive on hosts, in animal bedding, in carpets or in wild animal burrows. In San Francisco and the Bay Area, where conditions are moderate, fleas survive year-round.
If environmental conditions are poor, the emergence of adults can be delayed up to seven to eight months! The triggers that promote the emergence of the adult flea include exhaled carbon dioxide, body heat and vibrations.
Flea eradication begins with washing any blankets and bedding your pet has contact with. Vacuuming is believed to stimulate emergence of adults from the pupal stage, which are then more susceptible to eradication. Avoiding wildlife, which are reservoirs for fleas, will decrease the flea burden of your pet.
The pupal stage acts as a fortress, allowing new fleas to emerge continuously. Thus, treating the indoor environment with insect growth regulators (IGRs) that target and kill most of the larval and egg stages may be warranted. Sodium polyborate (Fleabusters) is effective in the home and “dehydrates” larvae. It is thought that larvae may also choke on the product itself, which is a fine dust.
For the outdoor environment, malathion, diazinon or other traditional insecticides are not recommended, as these chemicals are unsafe to both owners and pets. An alternative is a biological product containing nematodes (Steinernema), which tend to be more environment-friendly. These nematodes preferentially feed on parasitic larvae (fleas, cutworms, Japanese Beetles, etc.). They need some moisture periodically and may need to be replenished every few months.
Even more important than treating the environment is treating our pets. Immediate relief from itching can be achieved with corticosteroids and occasionally antihistamines and fatty acids. If secondary infections are present, the pet must be treated with oral antibiotics and occasionally antibacterial shampoos. Secondary infections can make itchiness exponentially worse.
In general, good-quality monthly adulticides – such as the topical spot-ons Advantage®, Frontline®, Vectra 3D® or Revolution® – or the monthly oral flea product Comfortis® are effective in killing adult fleas. Some of these products may “wear off” in about two to four weeks, depending on other factors, such as frequent swimming or bathing. Capstar® can be used for a rapid onset in flea death. It can also be used for long-term control on an every-other-day or every-third-day maintenance regimen. All pets in the household should also be regularly treated, as they can act as reservoir for fleas. In general, flea powders, shampoos and collars, while widely available, are not effective for animals affected with FAD.
In summary, flea allergy dermatitis is a very common skin disease in our pets. Diagnosis is based on history and physical exam findings. Treatment is aimed at minimizing flea exposure by treating the environment and avoiding wildlife, providing comfort to pets with antibiotics and anti-inflammatory medication, and preventing infestation with appropriate flea medication.