FELINE INFECTIOUS ANEMIA

(also called "Feline Hemotropic Mycoplasmosis" or infection by Hemobartonella felis, or
infection by Mycoplasma haemofelis or by Mycoplasma haemominutum or by Mycoplasma turicensis)

(Photocredit: Morguefile.com)

Parasitic organisms survive by attaching themselves to a host and using the host's body to thrive, generally at the host's expense. Parasites find themselves protected from the harsh temperature and moisture changes of the external world when they live within the rich, warm body of their host. The parasites this article is concerned with are special bacteria that attach themselves to the actual red blood cell membranes of their host, happily riding around, feeding and reproducing until the host's immune system sees them and begins destroying red blood cells in an attempt to remove them.

(original graphic by marvistavet.com)

Parasitic organisms survive by attaching themselves to a host and using the host's body to thrive, generally at the host's expense. Parasites find themselves protected from the harsh temperature and moisture changes of the external world when they live within the rich, warm body of their host. The parasites this article is concerned with are special bacteria that attach themselves to the actual red blood cell membranes of their host, happily riding around, feeding and reproducing until the host's immune system sees them and begins destroying red blood cells in an attempt to remove them.

Mycoplasma Haemofelis (formerly named Hemobartonella felis) and its smaller relatives

The agent of what has traditionally been called "feline infectious anemia" is an organism called Mycoplasma haemofelis." These creatures are technically bacteria but they are of a special type called "Mycoplasmas." Mycoplasmas are different from other bacteria because they do not have a cell wall surrounding and protecting their microscopic bodies. They cannot be cultured in the lab like normal bacteria because they must reside inside living cells. This feature not only makes finding them a little tricky but it also limits treatment to antibiotics that can penetrate inside of a hosting cell.

This graphic shows a number of red blood cells parasitized by Mycoplasma haemofelis.
The small dots within the red blood cells are Mycoplasma organisms attached to the outer surface of the red blood cells.
(Photocredit: NR387241 via Wikimedia Commons)

The term "feline infectious anemia" has also recently been felt to be inaccurate as there are many infectious organisms that might cause an anemia (lack of red blood cells). For this reason the disease itself has been re-named "Feline Hemotropic Mycoplasmosis" which literally means a blood infection of Mycoplasma organisms in cats.

Hemobartonella felis, as it was then called, was first discovered in Africa in 1942 but it was not recognized as a Mycoplasma until recently with the advent of gene sequencing. This has led to a renaming of Hemobartonella felis to Mycoplasma haemofelis, though after decades of celebrity under the original name many veterinarians will still refer to "Hemobart." Complicating matters further, gene sequencing has revealed two additional species, previously thought to be variants of Hemobartonella felis. These parasites, which are smaller, have been named "Mycoplasma haemominutum" and "Mycoplasma turicensis." They are much more common than Mycoplasma haemofelis but do not cause as serious an anemia as does M. haemofelis. That said, however, when they are combined with the feline leukemia virus, the former organisms tends to create serious bone marrow disease called "myeloproliferative disease" while the latter tends to promote the virus' cancer inducing abilities. It has been estimated that one cat in 5 is chronically infected with Mycoplasma haemominutum.

The infected sick cat is pale (sometimes even jaundiced) and weak. Anemic cats often eat dirt or litter in an attempt to consume iron. A fever may be present. The initial blood tests show not only red blood cell loss but evidence that the bone marrow (where new red blood cells are manufactured) has recognized that the body is losing red blood cells and is responding. A deficiency of mature red blood cells is evident but a large number of immature red blood cells are circulating, having been released prematurely to "take up the slack." This is called a "responsive anemia." Cats with concurrent feline leukemia virus infection tend to have more severe anemias as the virus does not permit the bone marrow to respond.

It can take up to a month after the initial infection before there are enough organisms to make the cat sick. It is this second month when organisms have reached peak numbers where mortality is the highest. If the cat recovers, it will become a permanent carrier though stress can re-activate the infection.

How is diagnosis confirmed?

Confirmation of diagnosis has been problematic since the first discovery of the organism in 1942. Because Mycoplasma haemofelis lives inside red blood cells, it cannot simply be cultured in the lab like other bacteria can.

Most reference labs scan all feline blood samples under the microscope looking for the characteristic appearance of infected red blood cells (see graphic at the top of the page). Unfortunately, the number of detectable organisms cycles in a matter of hours such that the number of visibly infected cells can change from 90% to 1% in a matter of 3 hours. This makes it very easy to miss infected cells even in a grossly infected cat. Luckily, all this microscopic scrutiny has been made largely obsolete by PCR technology. PCR testing uses a technique which amplifies very small amounts of DNA, allowing for detection of elusive organisms. Not only can Mycoplasma haemofelis be detected but the test can also detect and distinguish the smaller less harmful Mycoplasmas as well. Testing is best performed prior to antibiotics so to allow for best ability to detect parasite DNA. PCR testing is the best test to determine if a cat is suffering from a hemotropic Mycoplasma. PCR tests become positive 4-15 days after infection and peak in their ability to detect infection after 2-4 weeks.

(Photocredit: CDC Public Health Image Library)

What cats are at risk? The cats at highest risk are those that roam outside in the spring and summer (obviously these cats have the highest risk for flea infestation). Cats that are statistically likely to be infected are male cats younger than age 4-6 years, with a history of cat fights, and incomplete vaccination histories (in short, cats with somewhat casual care most likely including casual flea control).  Infection with the feline leukemia virus is also a factor in diagnosis. This may be because this immune-suppressive virus allows proliferation of the organism not possible in normal hosts or perhaps the anemia associated with the virus directly leads to a sicker cat who is thus more likely to see the vet and have testing. Making matters worse, the presence of the Mycoplasma seems to enhance the ability of the feline leukemia virus to create bone marrow cancers. An abnormal immune system is absolutely not a necessity in infection with hemotropic Mycoplasmas; normal cats are infected as well. Further, infection with feline immunodeficiency virus does not enhance the severity of hemotropic Mycoplasma infection as the leukemia virus does.

(Photocredit: Morguefile.com)

Blood sucking parasites such as fleas, ticks, lice, and mosquitoes are the leading candidates for spread of the organism. This makes flea control paramount in protection. Fortunately, there are numerous safe and effective products available to prevent flea infestation. Click here to view a comparison chart.

(Photocredit: Luiz Fernandez Garcia via Wikimedia Commons)

Cats can become infected by blood transfusion, though animal blood banks routinely screen donors so this is an unlikely route.

Infected mother cats appear to be able to infect their kittens though it is not entirely clear if this is done prenatally, through milk, or by oral contact. Oral transmission through bite wounds is thought to be possible but not confirmed.

Treatment

If hemotropic Mycoplasma infection is suspected, initiating treatment is probably a good idea as treatment is much easier than diagnosis. All Mycoplasma infections are susceptible to the use of tetracycline. In cats, the derivative doxycycline tends to be most easily dosed as it can be compounded into an oral suspension. Tablets must be used with caution as they can stick in a cat's esophagus, cause irritation, and scarring; liquid formulations can be made through a compounding pharmacy. The quinolone class of antibiotics (enrofloxacin etc.) are also effective against hemotropic Mycoplasmas. Three weeks of medication is needed to adequately suppress the organism. Complete clearance of the organism is not generally necessary unless the cat in question is immune-suppressed, felv-infected, has had its spleen removed, or is to be bred. If complete clearance is sought, sequential use of both doxycycline and a quinolone antibiotic can be used.

Killing the Mycoplasma is only part of the therapy, however; it is the host's own immune system which is removing the red blood cells and this must be stopped. Prednisolone or similar steroid hormone is typically used to suppress this part of the immune system so that the red blood cells are not removed as quickly. Very sick cats will probably require blood transfusions to get through the brunt of the infection. Happily, prognosis is fair if the diagnosis is made in time as cats generally respond well and quickly to treatment.

Carrier cats are generally not treated. As long as fleas are controlled, a carrier cat is not contagious.

Can dogs be infected?

There is an organism previously called Hemobartonella canis (now renamed Mycoplasma haemocanis). It is not generally considered to be a problem except in dogs who have lost their spleens and thus cannot effectively remove infected red blood cells. Gene sequencing suggests that this may actually be Mycoplasma haemofelis able to disguise itself slightly when it lives in a dog's body. Blood from infected dogs (via flea or mosquito) however, will not infect cats. It is not at this time clear, what the relationship is between these two Mycoplasmas but it appears that cats cannot infect dogs and dogs cannot infect cats. There is a hemotropic Mycoplasma disease in dogs but it is separate from that in cats.

Page last updated: 1/21/2023