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Flea Anemia in Cats and Dogs
Revised: April 01, 2023
Published: July 30, 2001

Cat in hospital cage with tubing and covered in blankets
After several days in the hospital, the outcome was a good one for this cat. Photo Courtesy MarVista Vet.

It is important to get the message out early: Fleas aren't just a nuisance. They drink blood, and blood loss can kill.

In almost every case, the owner had no idea that flea infestation could be lethal.

It is hard to imagine that something as tiny as a flea could be dangerous. We all know that fleas can make pets itch. Some of us are all too familiar with the spectacular skin inflammation in a flea-bite-allergic pet, but many people forget that fleas drink blood and that lots of fleas can drink a lot of blood. The physical state of inadequate red blood cells is called anemia, and when it is severe enough, it is a life-threatening condition.

Pets will not itch from their fleas unless they are allergic to flea bites. No scratching does not mean no fleas.

It is easy to underestimate a pet’s infestation. Only animals allergic to flea bites will itch from their fleas. This means that the animal who is not allergic to flea bites will not be scratching or losing hair. Thus the owner may not realize that the pet has a heavy infestation. If your pet is effective at licking and self-grooming, it may be hard to see the fleas, especially if the owner does not have a flea comb. Do not rely on your own ability to see the fleas; use reliable flea control regardless of what you see or do not see.

Check for Flea Dirt

The black, pepper-like specks found in an infested pet’s coat are actually bits of blood that have been sucked up by the flea and excreted in neat little packages to feed the larval fleas that hatch in the environment. Even if live fleas are not seen, flea dirt means that live fleas are there.

Who Are the Victims?

Cast and puppy in tall grass, touching noses

It takes a lot of fleas to produce enough blood loss to create a life-threatening situation for the host pet, but it still happens commonly. The following situations are high-risk for flea anemia.

  • Very young kittens being raised outdoors or by a mother cat who goes outdoors. Young kittens are small and do not have blood to spare. Furthermore, they are growing and trying to expand their blood volume; they are too young to groom themselves effectively and remove their own fleas. Flea anemia is probably the number one cause of death in open-household kittens.
  • Elderly cats who go outdoors. The elderly cat is often debilitated from other metabolic problems. Grooming is less efficient, besides which an older cat is just not strong enough to withstand much blood loss.
  • Outdoor puppies. Their situation is similar to that of the kittens’: too small to effectively groom and trying to grow in the face of ongoing blood loss.

Eventually, the weakness catches up with these animals, and they will die unless they receive a blood transfusion.

Evaluation and Treatment

The good news is that these patients can still be treated even fairly late in the course of the disease. Often they will need blood transfusions or transfusions with blood substitutes. They will also need to have their fleas removed and will ultimately need to be returned to an environment where they will be protected from further flea infestation.

The first step is recognizing the problem. This is not difficult for a trained veterinary healthcare worker, but it may not be easy for an uninformed pet owner. The affected animal will have pale gums (normal gums are shell-pink; anemic gums can be completely white). In advanced diseases, the patient will be listless and even cold. A flea comb can be used to check for flea dirt. Pets sometimes eat small pebbles, dirt, or cat litter when they are anemic in an effort to obtain more iron.

  • Be familiar with the normal color of your pet’s gums so that you can recognize a problem.
  • Regular flea combing can help nip a big problem in the bud.
  • Use flea control products all year round so you don't get caught with a surprise heavy flea burden in the spring.

A test called a hematocrit (HCT) or packed cell volume (PCV) is easily done in your veterinarian's office to assess the degree of anemia. The hematocrit or PCV reflects the percentage of red blood cells that should be in a sample of blood. In dogs, the normal range is 38 to 57; for cats, 24 to 45. Blood transfusions are considered when values reach 20 or less.

Ridding the critically ill patient of fleas can be problematic. Often the patient is too sick to tolerate the stress of a bath and is too young or too small for flea control products. In this situation, veterinarians have to use their judgment on what is the safest route to removing the fleas. It is worth mentioning nitenpyram (brand names Capstar®, PetArmor FastCaps®, and Capguard®) at this point as this simple product has greatly enhanced our ability to clear fleas from a patient quickly and safely. Nitenpyram is available as a fast-acting flea-killing tablet with no known side effects for mammals. It is labeled for use in animals weighing 2 lbs or more and begins killing fleas within 20 minutes of oral administration. While it does not have long-acting flea protection, its ability to rapidly remove a lethal flea burden has made it especially popular for use on patients with dangerous flea infestations.

Returning Home

Of course, after all the blood transfusions, heat support, and flea removal, the pet will ultimately go home, potentially to the same environment where the infestation occurred in the first place. Usually, topical flea control products will provide adequate future protection, and the use of a vitamin and iron supplement will help the patient rebuild red blood cell reserves. 

If the infestation is severe, consider treating the home environment separately before the patient returns to it. Your veterinarian can help you select safe and effective home treatments. The most important prevention is the owner's education.

There Is No Reason for a Pet to Carry a Flea Burden in This Day and Age

There are still common misconceptions among pet owners:

  • People commonly believe they have a flea bite sensitivity, and if they themselves do not perceive fleas biting, then there cannot be a significant flea burden. Fleas actually only bite people when they are newly emerged from their cocoons and are hunting for their permanent host. Waiting for a person to perceive a flea bite requires the flea population to have successfully established in the environment (i.e., the house) and progressed all the way to the production of new adult fleas. In reality, when the fleas are biting people, a significant population has been present for weeks or longer.

  • Many people believe that a pet with fleas will scratch or be itchy. In reality, only the pets allergic to fleas will be itchy.

  • It is also commonly believed that fleas are simply part of pet ownership and that there is no way to avoid them. This may have been true at one time, but, in reality, fleas have been optional for decades, with flea control methods achieving higher levels of convenience and safety each year. The days of sprays, powders, and foggers are largely gone, supplanted by chewable tablets and spot-on preparations. No pet needs to have fleas in the 21st century, and new products are being released every year.

The general pet-owning population has certainly heard of fleas and is aware of most of the modern flea control products. Yet, still, pets die from this easily preventable problem because people do not realize how serious it can be and cannot recognize when it has gotten to a serious point. Be proactive and keep up your flea control all year round; if you wait for what you think of as warm weather, your pet may well already be infested. Do not assume a pet with fleas will scratch. Do not assume that if the humans are not being bitten, then the flea burden must be light. Do not be one of those people whose beloved pet is lost to an easily preventable disease.

Compare flea-preventive products to help you decide which product is best for your situation. If you need help selecting flea control products, remember that your veterinarian and staff are professionally educated in this subject and will be happy to assist you.

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