Feline Infectious Anemia in Cats: The Flea-Borne Blood Infection
A cat that's suddenly pale, weak, and uninterested in food might be dealing with something a routine look wouldn't catch: a bacteria living directly on the surface of its red blood cells. Feline infectious anemia sounds like an older, vaguer diagnosis, and in a sense it is, the name has been updated as the science caught up with what's actually causing it.
What it actually is (and why the name changed)
What used to be called feline infectious anemia, or hemobartonellosis, is now more accurately known as feline hemotropic mycoplasmosis, caused by the bacterium Mycoplasma haemofelis (along with a couple of related, generally milder species). According to the Merck Veterinary Manual, genetic sequencing reclassified the organism from the genus Haemobartonella into Mycoplasma, which is why the name changed even though the disease itself hasn't.
How a bacteria on a blood cell causes anemia
Mycoplasma haemofelis attaches to the outside of red blood cells. The problem isn't direct damage from the bacteria itself so much as what happens next: the cat's own immune system recognizes the altered red blood cells as abnormal and destroys them, which is what actually causes the anemia. VCA Animal Hospitals notes that in an otherwise healthy cat, this can still cause acute, potentially severe anemia, not just a mild dip in red blood cell count.
How cats actually get it
Fleas are the suspected primary route of transmission, though the exact mechanism hasn't been definitively confirmed. Bite wounds from an infected cat, most often during a fight, are another well-documented route, which is part of why outdoor, unneutered male cats show up disproportionately in case data. This flea connection is a big part of why reliable flea prevention functions as disease prevention here, not just a comfort measure.
What symptoms actually look like
Lethargy, reduced appetite, and fever are the most consistently reported signs. Less commonly, a vet might find an enlarged spleen or jaundice (a yellowish tinge to the gums or eyes) on exam. Because these signs overlap with a lot of other illnesses, blood work showing anemia is usually what prompts specific testing for the organism rather than symptoms alone pointing straight to it.
Treatment and why speed matters
The bacteria typically responds well to tetracycline-class antibiotics like doxycycline. That's the encouraging part. The less encouraging part: a review on the clinical significance of hemotropic mycoplasmas notes that the more pathogenic form of the infection can be fatal in as many as one in three untreated cats, which is why prompt diagnosis and treatment, rather than a wait-and-see approach to a pale or lethargic cat, genuinely changes outcomes. Severely anemic cats may also need a blood transfusion and supportive care alongside antibiotics while their red blood cell count recovers.
Prevention comes down to flea control
Since fleas are the leading suspected transmission route, according to the ABCD's clinical guideline, year-round flea prevention is the single most practical thing an owner can do to reduce risk, particularly for cats with any outdoor access. Reducing fight risk (spaying and neutering, minimizing exposure to unfamiliar outdoor cats) helps too, since bite wounds are the other established transmission route.
Frequently asked questions
Is feline infectious anemia contagious to humans?
No, Mycoplasma haemofelis is specific to cats and isn't known to infect people.
Can indoor-only cats get this?
Yes, if fleas get into the home or if there's any contact with another infected cat, though the risk is meaningfully lower than for cats with regular outdoor access.
How long does treatment take?
Antibiotic courses typically run a few weeks, and while treatment usually clears clinical illness effectively, some cats can remain carriers of low levels of the organism afterward without ongoing symptoms.
Sources
- Merck Veterinary Manual, "Hemotropic Mycoplasma Infections in Animals"
- VCA Animal Hospitals, "Feline Hemotrophic Mycoplasmosis"
- "Haemotropic mycoplasmas: What's their real significance in cats?", PMC
- ABCD (European Advisory Board on Cat Diseases), "Guideline for Haemoplasmosis in Cats"
This article is for general information and isn't a substitute for advice from your own veterinarian. A pale, lethargic cat needs prompt veterinary evaluation.
