Flea Allergies

Photo-micrograph of a fleaWhen dogs and cats get fleas it is common for them to bite, chew, and lick obsessively, even to the point where they completely damage the skin. To us it makes sense that the bite of the flea is very itchy. However, it’s not the bite of the flea that technically makes the pet itch. Instead, it’s an allergy that animals have to a protein in flea saliva.

Flea Allergies in Dogs and Cats

That’s right. In our pets the incessant licking they do secondary to flea infestations is due to an allergy. The crawling and biting of the fleas itches a little, but it’s this allergy that makes the pet truly uncontrollably itchy.  And in fact, most allergies in pets – be they flea allergies, food allergies, or environmental allergies – cause itchy skin. You can read more about allergic skin disease in your pet here.

Most of the allergies we see in pets tend to present with similar signs in different animals. Flea allergies tend to present as itchy skin along the back towards the animal’s tail. This “caudal-dorsal” (caudal means toward the tail, while dorsal means up, or toward the pet’s back) presentation is a huge clue for us that the pet is suffering from fleas, even if we can’t find any on her.

In our experience, upwards of 90% of all dogs and cats suffer from flea allergies. And in the most severe of these pets, a single bite from a single flea is all it takes to trigger intense biting, chewing and scratching.

For the lucky 10% of dogs and cats that are not allergic to fleas, they may have dozens of fleas, and yet the owner barely sees the pet scratch at all. Because of this, it is not uncommon for us to see two animals from the same household that have completely different responses to their flea issues. Routinely, we’ll see a dog or cat present with extreme signs of flea allergies, including red, raw, bleeding, scabby skin, and severe hair loss, and yet we can barely find any fleas or flea dirt. Yet when we examine this dog’s brother, we find no sign of skin irritation, while simultaneously finding multiple fleas.

The reason for this apparent paradox is that the dog with severe flea allergies is aggressively biting and chewing and licking his skin. This flea allergy hypersensitivity causes the dog to severely damage his own skin, but it also means he’s doing yeoman’s work of removing fleas and flea dirt from his coat. That’s why it’s very common for us to have difficulty finding fleas on the coat of severely flea allergic pets.

The brother dog, on the other hand, has no allergy, and so barely licks at all. That allows the fleas to set up shop on his coat and feed and reproduce there. Ironically, the owners never think to look on this dog for fleas, since it’s his brother who’s scratching like crazy.

Diagnosing Flea Allergies

Diagnosing flea allergies is usually pretty straight forward. It starts with a dog that’s scratching and chewing obsessively, along with a caudal-dorsal bite distribution. The skin over the rump may have any degree of damage from a very mild red rash to a full-blown, scabby, bleeding, infected pyoderma (skin infection).

Seeing this bite pattern the next part of the exam is to run a flea comb through the pet’s coat from top to bottom. A flea comb is a small comb with extremely narrowly spaced metal teeth that catch any fleas or flea dirt (flea poop).  Flea dirt is small, black curly specs that resemble pepper.  Even if we can’t find fleas on the pet, we can usually find flea dirt. Any flea dirt at all is a clear sign the pet has fleas, and along with the chewing pattern described above means the pet is suffering from Flea Allergy Dermatitis (FAD).

Treatment for Flea Allergy Dermatitis (FAD)

Treatment for FAD is 3-pronged:
1.) Getting rid of the fleas
2.) Blocking the flea allergy
3.) Treating any secondary infections associated with the chewing and scratching.

Flea treatments have come a long way in just the last 2-3 years. Until recently, the commercially available topical treatments such as Advantage and Frontline worked very well. However, we now routinely see dogs and cats that have had these preparations applied religiously every month and yet are still covered with fleas. It’s clearly evident: Frontline and Advantage (and all their generics) absolutely do not work anymore.

Fortunately, there are multiple new preparations on the market that are very effective in treating fleas. One of the newest ones is Bravecto from Merck Pharmaceuticals. Bravecto is a chewable treat that most dogs love and will eat readily. The best part is that Bravecto is labeled to kill fleas and ticks for over 3 months. So one chewable treat and your dog is protected against fleas and ticks.

Unfortunately, Bravecto is not currently labeled for cats. However, there are other options available regarding flea control, and we can cover those with you when you bring your pet to us.

The second part of treating an FAD is to block the flea allergy. When a pet presents to us with and obvious FAD, that means they’ve had a flea issue for at least a little while, which means there’s probably some degree of flea infestation in the house and yard. That means it will take even the best flea products a while to work through the entire flea life cycle and make your pet flea-free. In the meantime, something needs to be done to get your pet to stop chewing.

In most cases, the only thing that is strong enough to block flea allergies is cortisone. This can come as a topical cream, an oral tablet or liquid, or as an injection. Each case is different, and we evaluate each case individually to make sure we give the pet maximum relief with the fewest side effects. Once the fleas are gone the cortisone treatment is discontinued.

The third component of treating an FAD is to treat the secondary infection. When dogs bite and chew themselves, they damage the skin and disrupt the natural immunity within it. This allows bacteria and yeast that is normal on every dog’s skin to get started as an infection.

Once these organisms get a foothold and start to flare up as a skin infection, they start to make the dog itch on their own. So even if we get rid of the fleas, these secondary infections make the pet continue to bite and chew and scratch, even long after the fleas are gone.

Treating these secondary infections is usually straight forward, and involve a combination of medicated shampoos and oral antibiotics. The main caveat here is that it can take weeks to months to get the skin to clear correctly. And treatment must be continued until the skin is completely cleared or the infection will just come right back.