How Dangerous Are Fleas?


PetMD Editorial

Published Jun. 13, 2016

by David F. Kramer

What Are Fleas?

Fleas are a class of wingless insects from the order Siphonaptera; they are parasites that live exclusively by hematophagy, the consumption of blood from a host organism. There are more than 2,000 species of fleas, and through evolution they have adapted to feeding on an extremely specific variety of hosts. There are cat fleas, dog fleas, and human fleas, as well as fleas that feed exclusively on singular species of rats, birds, and other animals—talk about being a picky eater!

Unlike other parasitic insects that have the help of wings to aid in their search for a host, fleas really have to sing for their supper. Well, not so much sing as jump. This doesn’t end up being too much of a problem for them because the flea is indeed the superhero of the animal world—at least in terms of leaping a metaphorical building in a single bound.

Fleas, which average between 1/6 to 1/8 of an inch in length, are capable of a vertical leap of seven inches, and a distance of more than a foot. For a six-foot human, this would be the equivalent of a jump 160 feet high and 295 feet long. In fact, only the froghopper (Cercopoidea) is a better insect Olympian. But it’s not all about power. When needed, a flea can also accurately leap less than an inch to get from one place to another.

The legs of fleas are highly developed, but they don’t rely on muscle power alone to jump. Rather, they store up a protein called resilin in a part of their body called the pleural arch. This highly elastic stuff can be primed and used like a spring to make these incredible leaps.

However, not all fleas jump, and this adaptation has much to do with their chosen hosts. The most adept jumpers feed on large animals. Those that have reduced pleural arches and can’t leap far feed on animals that either fly or nest.

Fleas: An Irritating Fact of Life

All of this makes for interesting trivia, but fleas are a fact of life for pet owners. A lion’s share of the pet care industry is devoted to products to combat fleas, as well as to prevent them from becoming an issue in the first place. If sales are any indication, this isn’t a battle that’s going to end any time soon. We can take a closer look at this war by talking to the folks who spend their days in the trenches: veterinarians.

“Fleas can cause a wide variety of issues for your pets,” says Dr. Adam Denish of Rhawnhurst Animal Hospital in Pennsylvania “The most common of which is flea bite dermatitis, which is a specific allergy to flea saliva.”

“It leads to intense itching and scratching for your pet. That constant itching allows the skin to break open and form scabs that can get infected. It can happen on any area of the skin,” says Dr. Denish, “but the most frequent site is the back and base of the tail. It can be treated by your veterinarian. It will need the removal of the fleas as well as medications for the allergy and infection.”

In addition to skin irritation and other external issues, pets are also at risk for internal complications from flea bites and infestations.  


 Internal Infections from Fleas

“A second problem caused by fleas is tapeworms. These are parasites that are passed to your pet when they actually ingest the flea,” says Dr. Denish.

“The tapeworm is initially inside the flea, and then grows inside your pet. They are segmented parasites that can be as small as 1/2 inch and look like maggots, but can also be as long as 12 inches. They can cause an itchy rear end as well as weight loss. But they are easily treated by your veterinarian.”

Another medical issue involving flea infestation on your pets is flea bite anemia. This is when young or small animals (such as puppies and kittens) have a severe flea infestation and the fleas feed so much on these animals that their red blood cell count decreases. Thus, they become anemic. This can be a medical emergency and even fatal in some cases if left untreated. Luckily, treatment by a veterinarian in a timely manner is usually able to reverse the effects.

Seasons Influence Fleas

The amount of time you must devote to fighting fleas has much to do with the climate where you live. In areas that experience freezing temperatures, fleas will either be killed by the cold or will lie dormant until warm weather returns. But the harsh winters of the northeast and northwest only provide a temporary respite from these pests, and those in warmer climates might find themselves battling fleas all year long.

“During the warmer months, from April to October, fleas are always found outside on wild animals and are hence found on the brush and bushes in the area,” says Dr. Denish. “When your pet comes in contact with the flea, the flea looks to your pet as a safe place for a meal.  Additionally, fleas can be on your clothing and come into your house that way.”

But pet owners always need to be on the lookout for fleas, even when the weather turns cool.

“Though most people think that fleas are only an issue in the spring and summer, don't ignore the fall,” says Dr. Denish. “In our practices, we tend to see more fleas from September to October as the cool weather leads the fleas indoors to your warm pets and houses. Fleas will die outside in the cold, but once inside, they can spend the winter. Also, most owners tend to stop flea treatment too early. We recommend year-round protection, or at least through two frosts.”

Fleas Are a Health Risk to Humans, Too

Dog and cat fleas don’t usually look to humans as hosts, but fleas in the home can still be a significant health risk to pet owners.

“Fleas can bite humans but don't actually live on human skin or hair. Certain diseases can be carried by fleas and spread to humans, including plague and cat scratch fever. If you have signs related to any of these diseases, consult your physician,” says Dr. Denish.

Getting Rid of Fleas – You May Need a Professional

Once fleas have begun to infest your home, it’s now time to turn to professional help; in the form of your local exterminator.

 According to Thomas Silvestrini, president of Custom Pest Solutions in Blue Bell, Pennsylvania, here are some of the methods an exterminator might employ to curb an infestation of fleas in the home:

“Often, pre-packaged aerosol products that contain an insecticide and a growth regulator are most commonly used by licensed professionals, which prevents fleas from molting to their final stage and becoming sexually mature,” says Silvestrini. “This combination is designed and tested to have enough residual life to outlast the flea life cycle, thus ending its reproduction cycle.”

While the chemicals professional exterminators use to kill fleas are generally safe, certain precautions do need to be taken once your home is treated.

“The pre-packaged aerosols applied to carpet and non-carpeted areas are safe when used according to the label. However, common sense should prevail.” Before allowing children to re-enter treated areas before they are completely dry, have them (and other humans) wear socks, shoes, or slippers. “The bottom pads on pet’s paws are very tough and the insecticide, in general, will not be absorbed,” said Silvestrini, but err on the side of caution and keep pets off of treated areas until they are dry.

“Some of the commonly used products are Precore 2625 premise spray and PT Alpine Flea and Bedbug Treatment, just to name a few, but there are many others. As mentioned, keeping children and pets off of treated surfaces until dry and following the labeled application rate will ensure safety,” says Silvestrini.

Unlike other parasitic infestations, such as bedbugs, you probably won’t have to get rid of possessions such as sheets, pillowcases, and clothing when treating for fleas. A run through a hot dryer should kill fleas, but it’s important that items be dried thoroughly, as damp bedding and clothes are a welcome breeding ground for more fleas.

“The only items that may need to be discarded would be severely infested items. Vacuuming several days after treatment will help to remove dead insects and stand the fibers of the carpet up, allowing any remaining fleas to absorb the insecticide easily,” says Silvestrini.

However, a single treatment from a professional exterminator might not be enough to keep your home flea-free for the long term.

“Homeowners need to be patient after a treatment. Depending upon the level of infestation, flea eggs may hatch for up to one month after the initial treatment, so immediate control and expecting not to see any fleas is not a reality.”

And while exterminators and pet care scientists have made great strides in fighting such infestations, fleas have also had thousands of years to step up their own game.

“Fleas are truly a significant cause of illness in our pets. It may sound trivial to say that fleas are a nuisance; they are much more serious than that,” says Dr. Denish. “Luckily there are great veterinary approved products to help prevent and treat your pet. Remember, preventing fleas is much better than treating for fleas.”

This article was verified and edited for accuracy by Dr. Katie Grzyb, DVM.


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