Visiting Veterinarian

A fly in the ointment and everywhere else

By Michele Gerhard Jasny V.M.D. - July 19, 2007

Ah, summer vacation. When I was a kid, it meant endless days of doing nothing, playing tag or kick ball with the neighborhood kids, gathering scraggly bouquets of wildflowers for my mother, and exploring the small woods in our suburban back yard. It meant sitting outside in the evening, getting eaten alive by mosquitoes and no-see-ums, then laying miserably in bed at night, too hot to sleep, picking at my welt-covered legs until they bled. My mother would say "those bugs sure love you" and "stop scratching" and "you must be allergic."

Mosquitoes and no-see-ums are both classified as true flies, belonging to the class Insecta, Order Diptera. The word Diptera comes from the Greek for "two wings," referring to the fact that true flies have a single pair of wings. Other "flies," like dragonflies, have two pairs, i.e., four wings, and belong to a different Order. The Order Diptera contains some 240,000 species of mosquitoes, gnats, and midges, many of which depend on the female having a blood meal in order for her eggs to develop properly. These bloodthirsty gals may feed on a variety of sources, besides people, and can carry all sorts of lovely diseases ranging from Dengue fever, to malaria, to West Nile Virus. Luckily, most mosquito and no-see-um bites in the United States just result in the classic itchy bump that disappears in a few days, but even a disease-free biting fly may cause a big problem in an allergic individual.

Take your cat, Midge. Do the margins of her ears ever get covered with crusty scabs in the summer time? Does she get little bumps or sores on her nose? If you see these things, take a minute and look at her paws, especially right along where the pad meets the furred skin. Midge's luxurious fur coat protects much of her body from mosquitoes, but her ears, nose, and the thin, hairless rims of skin along the margins of her pads are prime dining material. If you see any sores there, Midge is likely suffering from a condition called "ears, nose, and toes syndrome" caused by a hypersensitivity to mosquitoes. These cats react intensely to the bites and develop pruritus, alopecia, crusting, erosions, excoriation, ulceration, swelling, and macular depigmentation on the dorsal muzzle, pinnae, in front of the ears, around the eyes, and at the base of the foot pads. In plain English, Midge scratches until she bleeds, the affected areas swell up, lose hair, develop open sores, and generally look awful.

"Ears, nose, and toes" syndrome can have a sudden, severe onset or it can be more gradual and chronic. The swelling and lesions may be quite dramatic, appearing identical to a host of other nasty diseases including fungal, viral, or bacterial infections, autoimmune disease, even cancer. How do we diagnose mosquito hypersensitivity? One simple way is to keep Midge inside and see if the problem goes away. Another is to document if her symptoms come and go seasonally. It helps to do a number of tests, such as bacterial and fungal cultures to rule out other causes, but a skin biopsy is the most definitive diagnostic tool.

Treatment consists of corticosteroids, antibiotics if indicated for secondary bacterial infections, and minimizing mosquito exposure. If you can't make Midge into a house cat, at very least you should keep her in at dusk and at dawn. Reduce mosquito breeding by eliminating all standing water on your property. Unfortunately, because of cats' sensitivity to many chemicals, you can't use most mosquito repellants on Midge but a kitty-safe pyrethrin flea spray applied according to the package directions may help.

Your dog, Natty, is susceptible to a similar condition known as canine eosinophilic furunculosis in which the top of his entire snout may break out in bumps which become ulcerated and nasty. The lesions may spread all the way around his eyes and can be intensely itchy and painful. This syndrome may be a reaction to all sorts of insect stings from wasps to fire ants, spiders to mosquitos. It can also be caused by food or drug allergies, immune-mediated diseases, even stress. Treatment is the same as for Midge's allergy: corticosteroids, antibiotics if indicated, and insect avoidance. Allergic dogs may benefit from the use of Advantix (TM), a flea and tick product from Bayer that is touted to repel mosquitos. Advantix may be toxic to cats, so Midge can't use it, but it is safe to use on dogs.

How about horses? Yup, your friend Flicka can also be allergic to biting flies. The most common equine insect hypersensitivity is to no-see-ums, officially called Culicoides, and the syndrome seen in allergic individuals is called Sweet Itch. I don't know why. It's also called Seasonal Dermatitis, Summer Eczema, Summer Itch, or Queensland Itch if you're Down Under.

Other biting flies that may cause allergic reactions in horses include blackflies, stable flies, horn flies, mosquitoes, deer flies, and horseflies. Each species of insect has a different area of Flicka that it likes to munch on, and a preferred ambience and time of feeding. Culicoides like to bite horses around the mane and the tail, and prefer a decor of standing water, decaying vegetation, and manure. They are particularly active at dusk and dawn and like it when the air is still. Thus a poorly maintained farm on a breezeless evening will likely have a bigger problem than an immaculate farm on a windy afternoon.

Your average horse will simply find no-see-ums annoying but allergic individuals will develop hair loss, redness of the skin, papules, pustules, hives, or open sores. Flicka may be so itchy that she rubs off most of her mane and the head of her tail. Some horses rub so much they develop distinctive parallel strips of skin damage on their necks.

Mosquitoes like to dine on the sides of Flicka's body and are most active at dusk and right after sunset. They, too, like standing water. Black flies prefer running water and will bother Flicka's face more, as well as her ears, belly, groin, thighs, and the insides of her front legs. Horseflies? They bug Flicka during the daytime, lunching on the sides of her chest, her flanks, and upper portions of the legs. It is thought that insect hypersensitivity may be genetic in horses. Affected horses tend to get worse each year and, in allergic individuals, it only takes a few bites to cause severe skin problems.

If you haven't figured it out by now, treatment for Flicka is similar to that for Natty and Midge. First, reduce the number of biting insects in the environment. Eliminate standing water. Improve pasture drainage. Keep the barn clean. Use fly traps and fans. Next, you want to keep what flies there are away from Flicka. Keep her stabled for an hour before and after each side of dusk and dawn. Insect-proof her stall with fine mesh. If she's out, she can wear commercial sheets or hoods to protect her. Use fly wipes and sprays. Some veterinarians recommend Avon Skin-So-Soft as an insect repellent and the old folk remedy is a tablespoon of vanilla extract in a cup of water. If Flicka is still suffering, consult your veterinarian about the use of corticosteroids.

All these environmental steps are good for people, too. Fewer flies biting Flicka, Natty, and Midge means fewer biting you. Try some green alternative methods of control, too. Get a bug zapper. Better yet, buy or build some bat houses. Then you can sit outside on those endless summer evenings, doing nothing, and watch the bats eat the bugs, instead of the bugs eating you.