Itchy Dog Blog

This month I will discuss food allergy in dogs.  This first installment will describe how frequently food allergy is diagnosed in dogs with itchy skin.  In coming weeks, I will cover the clinical signs of food allergy, diagnosing food allergy, and feeding home prepared and/or raw diets versus commercial diets.

Food allergy, also known as food hypersensitivity or adverse food reaction, can result in skin or gastrointestinal conditions, or both in the same dog.  An allergy is an exaggerated immune response to a substance that most dogs tolerate without problem.  Food allergy may develop for the first time during puppyhood, or as an adult.  Most often they are young adults when signs first begin. Dogs may have eaten a food ingredient for years before developing an allergy to it.

The global pet food industry is a big, competitive business. It is expected to exceed $ 50 billion by 2015.  It is not surprising that more than 500 new foods are introduced every year to try and capture a share of the market.  Nor is it surprising that they are able to shape consumers’ perception of a condition like food allergy with their large marketing budgets.  According to an FDA web site “this [hypoallergenic] marketing niche was detrimental in two respects. The true nature and incidence of food allergies was clearly overemphasized and misrepresented.”

Walking through the aisles at your local pet store, you would think that every other dog must have a food allergy.  Claims like “hypoallergenic” and “natural” are found on nearly every bag or can of food.   What do these terms mean?  A food can be labeled “natural” if its ingredients are from animal or plant origin, or are mined.  They can still be labeled natural if ingredients are extracted, hydrolyzed, or fermented.  They may also contain synthetic nutrients and still be labeled as natural.

The true prevalence of food allergy in dogs is unknown, but it is almost certainly lower than many pet food companies would have you believe.  Based on a variety of studies, estimates of the prevalence of food allergy range from 9% to 36% of dogs with allergic skin disease. This probably translates to about 1-3% of all dogs.  Atopic dermatitis due to environmental allergens is much more common.  The majority of itchy dogs do not respond to strict diet changes, although it can be an important diagnostic step to take.  In the coming weeks, I’ll discuss the signs of food allergy and how to make an accurate diagnosis.

My two favorite flea products are Comfortis® and Trifexis®. Both products are once monthly, chewable tablets.  They contain an active ingredient against fleas, spinosad, and Trifexis also contains milbemycin which prevents heartworms and controls some important intestinal parasites (roundworms, hookworms, and whipworms).  Fleas take a blood meal within minutes of jumping on a dog. In this way they are quickly killed by spinosad, a chemical that is much, much safer for mammals than for insects by virtue of differences in the nervous system.

We used to hear that “even one bite” could cause flea allergy.  But, the number of mites DOES matter and Comfortis and Trifexis kill fleas more quickly than other products, minimizing the number of bites.  They are not affected by getting wet or bathing in the same way that all topical products are, making them the best option for my patients that often require frequent bathing.  Comfortis and Trifexis are prescription drugs that must be prescribed by your veterinarian.  The choice between the products will depend on your pet’s specific needs and other parasite control prescriptions.

Protecting your dog from fleas is much easier than it was 20 years ago. Back then, the best we could do was knock the flea numbers down, but it was challenging with the products that were available.  Lately, the problem is knowing which of the many products out there is right for your dog. I’ll give you my 3 favorites, starting this week with number 3:

Vectra 3D is at the top of my list for topical products (spoiler alert: the top two are given orally). It combats fleas (plus ticks and mosquitoes) on three fronts:

1.  One ingredient (dinotefuran) over-stimulates the fleas’ nervous system. It acts on an insect nervous system receptor, leaving a wide margin of safety for mammals.

2. The second ingredient is permethrin, which helps repel mosquitoes, kill ticks, and fleas.

3. The third ingredient is an “insect growth regulator” called pyriproxyfen.  This ensures that even if eggs are laid by a few surviving fleas, they will not result in an infestation.

Vectra 3D is quite safe for most dogs if applied according to the label, but always consult with your veterinarian for recommendations concerning your individual dog.

The final installment of common myths I hear about fleas

Flea Myth #5: “Product X was ineffective because the environment was so infested.” The observed effect of a product, measured in terms of the number of fleas that can be found on a pet, may indicate that this is true in the case of a heavy flea burden. However, it is all a matter of percentages.  If the product is even 90% effective, the manufacturer can claim efficacy.  But, even leaving 5% of hundreds or thousands of fleas will be too many for a lot of dogs or cats to tolerate.  The product may appear to perform adequately with a low flea burden in the environment, but not so well with a heavy burden, even though it kills the same percentage of fleas in both cases.

The fourth installment of common myths I hear about fleas

Flea Myth #4: “Cat and dog fleas don’t transmit diseases.” A number of important diseases are transmitted by fleas.

Cat scratch disease is caused by the organism Bartonella henselae.  It is transmitted between cats by fleas. Many cats are infected without showing any signs, but they can serve as a source of human infection. Scratches and bite wounds from infected cats may result in cat scratch fever.

Tapeworms are most often acquired by cats with the help of fleas, which they ingest during the normal course of their grooming behavior.

Murine (endemic) typhus, caused by can Rickettsia typhi, be transmitted by cat fleas that infest your pets or wildlife that may share your environment. Most case in the US are reported in southern California, Texas, and Hawaii. Signs in people include headache, rash, and body aches that may last for months if untreated.

Rickettsia felis may cause fever in people, and is considered a disease of emerging importance.  It is also transmitted by the cat flea, Ctenocephalides felis, the most common flea of dogs and cats in the US.

Myth #5 next week!

The third installment of common myths I hear about fleas

flea pyramid

Flea Myth #3: “We only saw a few fleas, so the house isn’t infested.” Not really.  Because fleas are reproductive machines, there can easily be hundreds of fleas in the environment for every adult you see.  Adult fleas are just the tip of the pyramid, and all the other life stages (eggs, larvae, pupae, pre-emerged adults) collect in the pet’s environment. And carefully flea combing for five minutes only turns up a fraction of the fleas on the average dog.  So remember, if you find even one flea, there are hundreds more maturing shortly!

Myth #4 next week!

The second installment of common myths I hear about fleas

Flea Myth #2: “He couldn’t have fleas because he hasn’t been around other dogs.” In fact, once a flea acquires a host (i.e. your dog), she has found her happy place. The old saying that “the grass is greener on the other side of the fence” doesn’t apply so well to fleas. They are content to stay on the same dog for their entire adult life span, typically 2-3 months. During this time, the female flea will be biting hundreds of times every day, and laying thousands of eggs that drop off into the environment. The environment is where the fleas wait to infest your pet (see Myth #1 for more details). So, it is not normally direct contact with another flea infested animal, rather just walking through the same premises as an infested animal, whether indoors or outdoors, that is the source of new flea infestations.

Myth #3 next week!