Dealing with Fleas

American Veterinarian®December 2016
Volume 1
Issue 3

Most people want to know only one thing about fleas: how to kill them. Flea control is much easier than it once was, though preventing fleas is still simpler than treating an established infestation.

Most people want to know only one thing about fleas: how to kill them. Flea control is much easier than it once was, though preventing fleas is still simpler than treating an established infestation.

How to Know if Your Pet Has Fleas

Fleas are tiny brown insects about the size of a pinhead. Their bodies are oval and flattened a bit from side to side. You can sometimes see fleas on your pet. If you try to capture a small insect crawling on your pet and it jumps an enormous distance (for its size), it’s probably a flea. If it’s attached to the skin, it’s more likely a tick.

Fleas can be hard to find if they are present in small numbers or if the pet has been chewing the skin. However, you might see flea dirt, which looks like black dandruff. Fleas are blood suckers, so flea dirt is actually digested blood that they have excreted. If you’re not sure if what you’re seeing is flea dirt, brush some of it onto a white cloth or paper and add a drop of water. If the wet dirt leaves reddish streaks on the white surface, it’s flea dirt.

Fleas can also cause a telltale pattern of hair loss. Dogs with hair loss on the lower back, tailhead, and inner thighs often have fleas even if no fleas can be found. Cats may have skin problems over a wider area of the body, especially the face and neck.1

Flea-Related Diseases

Fleas are more than just an itchy nuisance. They can cause a number of problems:

• Anemia: A heavy flea infestation can cause anemia and even death from blood loss.

• Transmission of infection: Fleas carry bacteria and parasites that can infect both pets and people, including the following:

  • Tapeworms
  • Typhus
  • Tularemia
  • Bartonellosis (cat scratch disease)
  • Plague2

Why One Dose of Flea Tretment Isn't Enough: The Flea Life Cycle

The most common flea species affecting dogs and cats in the United States is Ctenocephalides felis, the cat flea. Cat fleas survive best in warm, humid climates and have a 4-stage life cycle1,2:

• Eggs: Fleas deposit eggs in their host’s fur; the eggs then drop into the environment.

• Larvae: Eggs hatch into larvae, which develop in protected areas away from sunlight like carpet fibers and shaded places outdoors.

• Pupae: After a few days to weeks, larvae spin cocoons and become pupae. Pupae can remain stable in their cocoons for months if they do not dry out. Pressure, carbon dioxide (from breathing), and increased temperature all stimulate pupae to develop into adults. Simply walking around a room can trigger the emergence of adult fleas, even if the room has been vacant for weeks or months.

• Adults: Most adult fleas emerge within a month after pupa formation. They jump onto a passing host and begin feeding right away. Females usually lay eggs within 24 hours.

By the time you notice fleas, they have already begun laying eggs.3 Larvae and pupae that are still in the environment continue to develop. After you use a flea control product that kills adult fleas, more will emerge over the next few weeks. These newly emerging fleas are the reason to use a flea product that has residual activity and to continue using it for several months.

Flea Prevention

The Companion Animal Parasite Council recommends the following2:

• Treat all dogs and cats with flea control products yearround for life.

• To eliminate an established flea infestation, treat all pets in the home and understand that controlling the infestation could take months.

• Consider flea infestations a public health concern.

Very effective flea control products have become available in the past several years. Talk to your veterinarian about the best product to use on your pet; many are available by prescription only.

If you are considering over-the-counter products, be aware that those containing synthetic pyrethrins, including permethrin, can be toxic to cats. Flea combing is the safest way to remove fleas from puppies and kittens that are too young for flea products.4

You might see fleas after using a recommended product even if you have followed label instructions and treated all household cats and dogs. This does not necessarily mean that the product failed. It takes time for all of the pupae in the environment to develop into adults. Many of these products kill adult fleas before the females can lay eggs, so in time the flea population will be eliminated because no new eggs are being laid.

Dr. Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC.


  • Overview of fleas and flea allergy dermatitis. Merck Veterinary Manual website. Revised December 2014. Accessed March 31, 2016.
  • Fleas. Companion Animal Parasite Council website. Reviewed June 2015. Accessed March 31, 2016.
  • Dryden M. The case for year-round flea and tick control. Companion Animal Parasite Council website. Accessed March 31, 2016.
  • Safe use of flea and tick preventive products. American Veterinary Medical Association website. Accessed March 31, 2016.
Related Videos
merck leptospirosis panel
merck leptospirosis panel
merck leptospirosis panel
dvm360 Live! with Dr. Adam Christman
Vet Perspective parasitology discussion
Vet Perspective parasitology discussion
Vet Perspective
© 2024 MJH Life Sciences

All rights reserved.