Fleas – Those Blood Sucking Little Vampires!

Fleas – those blood sucking little vampires

February 27, 2014

From the desk of Dr. Voorheis

To produce a mighty book, you must choose a mighty theme. No great and enduring volume can ever be written on the flea, though many there be that have tried it.” (Herman Melville)

Well, I’m going to try it! But you might be asking “are you kidding me Doc? A whole blog devoted to fleas?” Yes, absolutely! With regard to the amount of disease and visits to the veterinarian regarding fleas and flea related illness, I could devote two blogs or more! You’ll come to realize that I am NOT a fan of fleas…nor should you be. They are the enemy.


From Wikipedia: Fleas are wingless insects (1/16 to 1/8-inch (1.5 to 3.3 mm) long) that are agile, usually dark colored (for example, the reddish-brown of the cat flea), with tube-like mouth-parts adapted to feeding on the blood of their hosts. Their legs are long, the hind pair well adapted for jumping: a flea can jump vertically up to 7 inches (18 cm) and horizontally up to 13 inches (33 cm),[3] making the flea one of the best jumpers of all known animals (relative to body size), second only to the froghopper.

Charming, right? That’s just the beginning. Historically, fleas have been the harbinger of tragic, wide spread illness. The most famous instance was “The Black Death” or “Black Plague” which decimated Europe in the mid 14th century, wiping out roughly 1/3 of Europe’s population. More than 75 million people lost their lives. This plague was caused by a bacterium called Yersinia Pestis and you guessed it, it was carried by fleas. These fleas lived on rats that traveled on merchant ships from the Far East to Europe. We still see plague today, such as the bubonic plague, which is still caused by the Yersinia Pestis organism. And yes, this is still carried by fleas. The charming little flea that carries it is found on ground squirrels and other rodents. Every now and then, we will read about a campground in the local mountains being shut down because plague was found in a ground squirrel. The good news is that the disease is now easily treated with the tetracycline class of antibiotics.  

“Ok Doc, nice history lesson. But what about my pets?” Nope, not yet. Sun Tzu’s second century book, “The Art of War”, tells us to “know our enemy”. So let’s learn a little bit about the flea that likes to make a convenient meal of our pets.

The most common flea that affects both our dogs and our cats is the cat flea, Ctenocephalides felis. Virtually all of the fleas affecting both dogs and cats in the United States are the cat flea. Fleas have 4 life cycle stages which are eggs, larva, pupa and adult.

Below, you’ll find a picture of an adult flea. In the words of a line from my favorite movie, Ghostbusters, “it’s an ugly little spud isn’t it”?


So, what came first, the chicken or the egg?  I think we should start with the egg and work our way forward. 

Eggs:  These are tiny white fleas eggs can hatch in as little as two days, or as long as few weeks depending on environmental conditions. The eggs can be found where the pet sleeps, on bedding, carpet, floor boards etc.

Larva: The larval stage is skinny, long and semitransparent. It has small hair on its body. They eat the feces of adult fleas, made mostly of dried blood. Depending on the amount of “food” and other environmental conditions, this stage can last from 5 to 18 days. The larva then spins a cocoon.

Pupa: The cocoon phase. This is the last phase before emerging as an adult. The adult flea can emerge in as little as 3 to 5 days, or it can stay in the cocoon phase waiting for the right time to emerge.

Adults: Emergence is stimulated by vibration, warm ambient temperatures, high humidity and increased CO2 levels. They are about 1 to 3 mm in size, reddish brown to black in color and possess powerful hind legs to jump and run through the animal’s hair coat. Adult fleas begin feeding immediately once they acquire a host and defecate flea feces (digested blood) in as little as 8 to 9 minutes. Adult cat fleas require blood to produce eggs. This is the only stage in the life cycle when the fleas live on the pet. They live 4 days to a couple of months and can lay up to 50 eggs a day. Yikes!

So let’s add it up:

  • Eggs can hatch in as little as 2 days.
  • Larval stage lasts from 5 to 18 days
  • Pupal stage – 3 to 5 days
  • Adult – A flea can go from egg to adult producing eggs in as little as 11 days in optimal conditions.

Optimal living conditions for an adult flea can be defined as Southern California spring, summer and fall. Less optimal is winter time, however we NEVER get cold enough to stop fleas altogether.


So what’s the big deal?

“So what is the big deal Doc?  A little itch? Fido scratches a bit? Big deal.”  

It actually is a big deal. Close to 70% of the itching, scratching dogs that are presented at a veterinary hospital have flea bite dermatitis or flea bite hypersensitivity which we commonly call flea allergic dermatitis.  That is a huge number of cases. To be more accurate, flea bite dermatitis is caused by direct irritation at the site of the bite while flea bite hypersensitivity is caused by immediate (type 1), delayed (type 4), and cutaneous basophil hypersensitivities.

Have you ever seen tapeworm segments in the feces of your dog or cat? I know, gross! Dogs and cats get tapeworms from ingesting fleas. Fleas get tapeworms from the flea larval stage ingesting tapeworm eggs. If your pet has tapeworms, your pet has fleas. Bottom line, end of story. I told you fleas were the enemy!

Every year, we see kittens, puppies, and less mobile older dogs that are suffering from such a large flea load that they are actually anemic. In case you didn’t catch that I will say it again – ANEMIC….caused by fleas! Those blood sucking little vampires.

Flea and other parasite control is essential to your pet’s good health. Essential. I will describe the best methods of flea control below, but for now I will talk about the skin disease caused by fleas. It isn’t pretty and it can make your pets absolutely miserable.

Flea bite dermatitis and flea bite hypersensitivities are the most common form of skin allergy in the dog and cat, comprising 70% of all skin allergies in dogs, and approximately 50-60% of all skin allergies in cats.

Flea saliva contains histamine like compounds, several complete allergens and haptens which are substances that when combined with other molecules act like allergens.

Do you remember my description of the allergic reaction? Type 1 reactions are a form of acute inflammation that results from the interactions of antigens, i.e. in this case the proteins in a flea’s saliva with mast cell bound IgE which is a type of antibody. This leads to the release of mast cell contents which in turn cause acute inflammation. This excessive release of inflammatory mediators is also happening with other cells in the skin like white blood cells called eosinophils and basophils. The end result is a very itchy, miserable dog.

Flea allergies are also type 4 hypersensitivities where the itching can occur days after the bite. This type of inflammation is mediated by different cells called T-cells.

The important take home point here is that allergic reaction from flea bites can be immediate, and can also be delayed. You don’t have to find fleas on your dog or cat for the pet to have flea related skin issues. That is worth repeating. Remember my second blog, in which I talked about the microbial world we all live in. Somehow, we humans would like to think we are above all that and we extend that vision to our pets. As a clinician, I am not judging you if your dog or cat as a flea allergy. I don’t make an assessment as to your housekeeping or general character if the dog or cat has an allergy to the bite of a flea. Many people are actually offended when I talk about flea allergies. Comments I often hear are things like “my groomer has never seen fleas on my dog”, “I’ve never seen a flea on my dog”, “my cat couldn’t have fleas – it’s in the house all the time”, “I give yeast tablets so they can’t have fleas”, “I add garlic to the food to repel fleas”.

All and I repeat all dogs and cats in Southern California, unless they are residing in a plastic bubble, will pick up fleas. Some more than others, and some with bigger reactions to fleas than others.

What does a flea allergy look like?

The textbooks say the age of onset of a flea bite hypersensitivity is usually 3 to 5 years. My experience is that I have seen flea allergies start as soon as 15 months of age and in some cases even younger. They tend to worsen with age, with fewer and fewer flea bites required to stimulate the allergic response. It tends to develop with intermittent exposure to fleas as opposed to continuous exposure. The same holds true for cats. Please do not take that as a reason to not treat for fleas.


Some signs to look for are:

  • a mild rash (small red bumps)
  • broken hair follicles (from chewing)
  • significant itching on the BACK half of the body

Hair loss and itching occur especially in a “triangular patch”. This looks like a backward “V” extending from the base of the tail to the middle of the back. The back of the thighs, the tail and the area of the belly between the rear legs are also affected. The incisor teeth will even wear down with chronic chewing.  


Secondary skin infections with both bacteria and yeast organisms are common especially with chronic conditions. These secondary skin infections complicate treatment, requiring additional treatment to resolve the patient’s discomfort.

Dogs with flea allergies will also develop painful “hot spots” or “pyotraumatic dermatitis”. These are deep skin infections and inflammation associated with the trauma of scratching an itchy spot.

In cats, this often takes on the appearance of a skin condition called “miliary dermatitis” which can be generalized over the cat’s entire body or confined to the same area as the dog seen above. The other place we see it is the head and neck region. Cats also get a condition called “eosinophilic plaques” which can be caused by flea bites.


Differential Diagnosis

Whenever a case of “itchy skin” is presented to me, I have a mental checklist to go through. Many dogs and cats have multiple allergies but fleas and flea bite hypersensitivity must be brought under control prior to tackling those other conditions. So I have to bear in mind that the apparent flea bite hypersensitivity in front of me could be a food allergy or atopic dermatitis masquerading as a flea allergy. I may require skin scraping to determine whether or not one of three different types of mange may be involved, those being sarcoptic mange, demodectic mange and chelyetiella mange. I also may perform cytology on the skin to determine the level and type of secondary skin infections contributing to the skin disease.

It is my experience, that flea bites and flea bite hypersensitivity are not glamorous diagnoses. Folks would much rather have their dog allergic to food than fleas. Think of it, a brightly lit store with an “oh so friendly” helper in a blue shirt, solving your dog or cat’s problems with a bag of food. Unfortunately, things don’t usually work that way.


There are two forms of treatment. First, we must treat the affected pet. The dog or cat brought in with the kinds of signs mentioned above is miserable. We must bring some relief to that patient. Flea control and flea elimination will be a critical factor in treatment. However, the dog or cat is itchy now. Relief of itching can be accomplished by using a variety of anti-inflammatory medications. Relief of itching may also involve use of antibiotics and antifungals to treat secondary bacterial and/or yeast infections. Relief of itching may be brought about by the use of topical or systemic corticosteroids, omega-3 fatty acids, anti-histamine therapy, or the new medication Apoquel. Corticosteroids and Apoquel are used to get the majority of the inflammation under control while flea control measures are undertaken. In mild cases, relief may be achieved by a combination of topical corticosteroids, omega 3 FA’s and flea control. In more significant cases, systemic corticosteroids or Apoquel will be needed to bring the inflammation under control and relief to the pet. Traditionally, that control may look like an injection of a corticosteroid and oral corticosteroids to bring about relief. In January of this year, a new medication to control skin inflammation called Apoquel was released and it has been proving very effective at controlling skin inflammation and itch thus far. Its cost per pill is higher than corticosteroids, but is about the same as what you would pay if an injection of corticosteroids was given along with a prescription to take home.

A word about corticosteroids. It is my belief that the judicious use of corticosteroids is safe and effective. The key word is judicious. Most of us in veterinary medicine are reluctant to use them long term because over the long haul they can have side effects. Appropriate management involves discussion with your veterinarian and monitoring your pet. It may include laboratory work to assess how the animal is handling the medication.

For the most part, both Apoquel and corticosteroids can be used the same way in flea bite hypersensitivity reactions. We use them to get the inflammation under control and use our flea control to keep things that way.

What about omega-3 fatty acids and/or antihistamine therapy? Omega 3 fatty acids work their way into an inflammatory cascade, blocking the body’s ability to make arachidonic acid which is a key component of inflammation. This is effective in both arthritis and skin inflammation but slow to work and certainly cannot “hold” the severely affected dog. The dose is 180 mg of the EPA fragment per 10 lbs of dog per day. This means a 40 lb dog would require 4, 1000 mg fish oil capsules per day. There are super concentrated forms available.

Antihistamine therapy? We all use it to try to decrease the amount of corticosteroids used to control itching. I think if you actually pin down a veterinary dermatologist they will admit that antihistamines are not very effective at all in controlling itching in the dog and cat. This is mostly because histamine is not the main chemical mediator of inflammation in our pets.

What about cats? Can we use this new anti-itch medication in cats? Sadly, no. Once again, I must remind everyone that cats are not small dogs. Dogs and cats have entirely different metabolisms and this new drug is not tolerated in cats. And while we are on the subject, cat flea control should NEVER EVER be applied to a dog and dog flea control should NEVER EVER be applied to a cat. Did I say NEVER EVER? Good. Cats bring the added challenge of sometimes being a little reluctant to be medicated. Again, corticosteroids may make up an important part of inflammation relief. However, the type of corticosteroid and the method of its administration mandate a discussion between veterinarian and client. In some middle aged and older cats, corticosteroids may not be used and a drug called cyclosporine will be substituted.

The prime aim of treatment of flea bite dermatitis and flea bite hypersensitivity is flea control. Appropriate treatment will be directed against certain life cycle stages mentioned above. Remember that we and our animals live in a microbial world (second blog) and the organisms we are trying to eliminate and control will, over time, develop resistance to the products designed to eliminate them. In fact, continued use of these products will exert selective pressure on flea populations and will most likely result in resistant flea populations.

New populations of fleas are being brought into our yards by untreated animals, feral cats, raccoons, and opossums. In suburban United States, the raccoon is a main carrier of fleas.

There is no question that those of us on the frontlines of daily flea treatment believe we are in a situation that is worsening with regard to flea related illness. There are some basic principles that need to be followed if we are going to achieve success in treating fleas and flea bite hypersensitivity.

1. Every animal in the household, symptomatic or not, needs to be on a monthly flea control program. That includes the outside dog with no skin problems and the cat who “never gets fleas” along with his brother who “always gets fleas”. Please understand that in that situation, the cat who “never gets fleas” may have just as many fleas as the cat who is symptomatic for his/her flea allergies.  That can be daunting for those of us who have multiple cat/dog households. The bottom line whether you like it or not is: Everybody. Every month. Did I say every animal in the house every month? I hope so.

2. Understand that the only life cycle stage of the flea that lives on the pet is the “adult”. The larva, the pupa, and the eggs are in the environment. Where? Here’s a hint: wash the bedding where the dog or cat sleeps at least once a week. Vacuum your carpets at least once a week.  Fleas hide and do their business in these areas.

There is a dazzling array of flea products with more being produced every year. In addition there is a large number of products that are claiming to be “just like” a well known or better product with slick packaging and.box store prices. Many of these are recycled products that the veterinary profession knows are ineffective and in some cases not all that safe.

The following is an abbreviated list of products that are available. I will make some recommendations but please keep in mind that as it is with vaccinations, not every animal needs the cookie cutter recommendations for flea control. Depending on housing, skin problems and multiple animal households, we make different recommendations for your pets. I prefer to treat the individual pet and not make blanket recommendations.


Program, Advantage, Advantix, Advantage-multi, Advantage II, Topspot, Frontline, Frontline Plus, Parastar, Parastar plus, Knockout, Ovitrol, Adam’s Spray, Biospot, Preventic Plus, Revolution, Sentinel, Capstar, Promeris, Vectra 3D, Comfortis, Trifexis.

For some dogs and cats with flea bite hypersensitivity, a topical adulticide applied monthly to every animal in the house will work and will be effective. The key is every animal, every month. There are veterinary parasitologists who recommend that you rotate products to try and prevent resistance to product. For example, I might recommend Revolution applied every month to all pets in the house for six to nine months and then rotate in with Comfortis for six months. The same thought process can still be used using Frontline or Advantage, although for these two older products I am currently recommending the application frequency be changed to every 3 weeks.

For dogs with the severe flea bite hypersensitivities, consider using two products. For example, use Revolution once a month, e.g. on the first of every month along with Sentinel every month, e.g on the 15th of every month. The revolution would act as an adulticide and the Sentinel as a flea sterilizer. Fleas that lay eggs after ingesting the blood of a dog who takes Sentinel will not hatch.

There are some dogs whose flea bite hypersensitivities have resulted in such severe skin disease that frequent bathing will be needed. “Wait a minute Doc, am I going to wash off product”? Yes. For those dogs I would recommend Comfortis once a month AND Sentinel once a month. The products will still be on the dog even if they have to be bathed once a week. For severely affected cats, very similar recommendations in that Comfortis and Program should be used.

The bottom line is a conversation with your veterinarian is going to be needed to decide together what flea products are necessary in your home, for your pet or pets.

Treatment failures

The number one reason for treatment failures is interrupted or intermittent flea control. Poorly applied or inadequately applied product is also a big problem. Another epic failure is treating only the affected dog or cat and ignoring the pets who have fleas but don’t have flea allergies. How many people apply monthly product, but give their dogs and cats weekly or biweekly baths? Poor products are another problem. Those products being marketed as “just like” the better products mentioned above, but somehow the magic of Wal-Mart or Costco makes them cheaper. Don’t believe it. Problem is they contain product that we discarded as effective more than 20 years ago. Recycling and repackaging ineffective product has become commonplace. Buying these products saves a few dollars now but believe me when I tell you that you will spend A LOT more money later treating the dog or cat that is now infested and miserable because the bargain stuff didn’t work properly. You get what you pay for, buyer beware. Your pet’s well being is worth a lot more than a few dollars saved, is it not?

As I mentioned above, a flea allergy is not glamorous.  It seems like people would sooner have their pets allergic to food or have atopic dermatitis. Atopic what?  We shall talk about these two topics next week. I hope you have enjoyed your crash course on fleas and flea prevention…on a parting note I will say once more….. : Everybody. Every month. Did I say every animal in the house every month? I hope so.

Until next week…………………….

Dr. Voorheis

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