Insect bite allergy: Fleas, mosquitoes and Culicoides (Proceedings)


The diagnosis and management of insect bite allergy is still an important part of my specialty practice. I diagnose on average 2 to 3 new cases per week.

The diagnosis and management of insect bite allergy is still an important part of my specialty practice. I diagnose on average 2 to 3 new cases per week. With all the safe and effective insect control products currently on the market, you would expect these numbers to be lower. But because of these wonderful products, we sometimes are neglecting to explain good flea control to our clients. This is unfortunate, since flea allergy dermatitis is relatively easy to control but is extremely uncomfortable if left untreated.

The diagnosis of flea allergy dermatitis (FAD) is based primarily on history and clinical signs. Some of the clues that lead you to the diagnosis of FAD are a history of fleas in the environment and on the pets, indoor/outdoor cats, no existing flea control program and exposure to other pets and environments outside the family. The most common clinical signs include moderate to severe pruritus, the presence of fleas or flea dirt, and the loss of hair on the lumbosacral area and caudal thighs. Some dogs will also "corn cob" or chew their forelimbs. As time goes on, many of these dogs will develop secondary yeast and/or bacterial pyodermas. The diagnosis of FAD is confirmed by intradermal testing with flea antigen or by response to complete flea control.

To accomplish complete flea control as quickly as possible, flea feeding must be kept to a minimum. Unfortunately, this is not as easy as we would like, even though we have multiple safe and effective products available. The reasons for this vary, but may include unrealistic expectations of these products on the part of practitioners and clients. Remember that fleas are not killed instantaneously by any of the products, nor are any of the products 100% effective all month against every strain of fleas. Because of differences in the products' speed of kill, some products may take longer than others to achieve complete flea control. Also, it must be remembered that the time to kill increases and the percentage of fleas killed decreases as the month progresses. Therefore, if the environmental infestation is not controlled, the client will probably see fleas on the pet by the end of the month. This does not mean that the product is ineffective, just overwhelmed. None of these products present an impenetrable barrier to fleas. The fleas will still jump on the pet and may be present several hours before dying.

Another obstacle to accomplishing complete flea control is the lack of client education about the flea life cycle. Informal surveys have revealed that veterinarians may not be explaining the flea life cycle to their clients. Clients need to understand that only the adult flea spends its life on the pet and adult fleas make up only 5% of the entire flea biomass. The adult flea can start to feed within 10 minutes and start to lay eggs within 24 to 48 hours after feeding. The eggs are laid on the pet, but soon drop off into the environment where they hatch and develop into larvae. In a few days the larvae become pupae. The flea can remain in the pupal stage for as short as a week or as long as 6 months, depending on environmental conditions. The pupae are also extremely resistant to all current flea control products. It is the adult fleas emerging from these protected pupae that can cause a re-infestation 3 to 6 months after an environment has been treated effectively.

Inappropriate use of topical flea control products also leads to failure to achieve complete flea control. Bathing and swimming may increase the kill time and decrease the kill percentage for any of the topical products. The only products not affected by water exposure are the oral products. Flea control products must be applied at the proper interval and in the appropriate doses if they are to be effective. All pets in the household must be treated to control infestations.

The final obstacle to reaching complete flea eradication is inappropriate or no environmental flea control. Many dogs no longer live in closed environments. They now go everywhere with their owners. This means they come into contact with many more dogs, other animals and environments that can reinfest them and their home environments with fleas. Many clients now have natural landscaping that exposes pets to more wildlife and to a more flea friendly environment. Finally, more clients are averse to using "poisons" in their yard or home.

Resistance to current flea control products at this time is not an obstacle to complete flea control. Monitoring efforts indicate that true resistance is extremely rare. But flea experts warn that this does not mean that resistance will not occur with continued use of these products.

What can you do to help your clients achieve successful flea control? First, give them a better idea of what to expect from the product they purchase. Be sure to tell them how long the product takes to work and how well the product works after bathing. Also, be sure the client knows that they may still see fleas for a while. Second, the client must understand how to appropriately apply the product, how often to apply and when to apply after bathing. Third, be sure the client understands the flea life cycle and explain why they may see fleas several months after starting therapy. Finally, the client must do some environmental flea control. Frequent vacuuming can remove significant numbers of flea larvae from the environment. Regular washing of dog bedding is also helpful. Using ovicides/larvicides (lufenuron, pyriproxifen, methoprene) on all pets or environmental application of larvicides (pyriproxifen, methoprene)will speed resolution of a flea infestation. If the infestation is severe, spraying an adulticide (usually permethrins) in the house may also be helpful. Outdoor environmental control may consist of removing mulch and leaf litter, as well as eliminating pets' access to humid, dark places. Pyriproxifen (larvicide) or the beneficial nematode Steinernema carpocapsae can be applied outdoors to control immature flea life stages. Adulticides (usually permethrins) can be used initially if the infestation is severe. Client education is the key to successful flea control for the allergic dog. Targeting both the adult flea as well as the immature life stages is the key to delaying the development of flea resistance to the newer generation of flea adulticides. And both of these facts illustrate why it is important that flea control products be dispensed by a veterinary clinic rather than through over the counter channels. Put in flea control handout and client questionnaire?

Allergy to the bites of mosquitoes or Culicoides spp. can cause symptoms similar to flea allergy dermatitis. In our specialty practice in Florida, this is a fairly common hypersensitivity. Unfortunately, awareness of these allergies is not widespread and therefore they go undiagnosed and untreated. The history usually includes proximity to water, access to the outdoors, and sometimes owner complaints about biting insects. Regular screening is usually an effective barrier against mosquitoes, but not Culicoides spp. As mentioned above, clinically hypersensitivity to these insects can look similar to flea allergy dermatitis. They can also cause generalized pruritus and granulomatous lesions. Diagnosis is made by intradermal testing with mosquito and Culicoides antigens (available from Greer laboratories). If intradermal testing is not available, diagnosis can be made black of response to flea control and resolution of signs after the use of insect repellents. Permethrins are currently the best therapy. Dogs must be treated daily with low concentration sprays or gels (less than 1% permethrin) and one to two times weekly with high concentration sprays (2%). Some of the spot on flea control products also contain permethrin. These may be used for insect repellency but may need to be used more often than once a month, especially if pets are bathed frequently. Other ways to help control mosquito/Culicoides hypersensitivity are to keep pets in at dawn and dusk when the insects are most active and to use environmental insect control. Some patients or owners may be sensitive to permethrin. In those cases, skin so soft or other natural repellent products containing plant oils may be tried.

For any insect bite allergic dog, steroids should be available at home for quick use. This can avoid a serious outbreak and secondary infections if the steroids are used immediately after the clients notice an increase in pruritus or after known insect exposure. The dose of oral prednisone should be 0.5 to 1 mg/lb daily for 3 to 5 days. If the patient is still having problems at this point they should be seen.

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