Feline hemotropic mycoplasmosis is an infectious disease caused by the parasite Mycoplasma haemofelis. It causes hemolytic anemia, a type of anemia where the body destroys its own red blood cells because they "look different" to the immune system. The disease was first described in the United States in 1953.

The causative agent, Mycoplasma haemofelis, is a parasite that affects the surface of feline red blood cells. A large study performed in 1990 helped establish the prevalence of Mycoplasma haemofelis in the general cat population and identify risk factors. The prevalence of feline hemotropic mycoplasmosis was determined to be 4.9 percent in all cats. As might be expected, in healthy cats the prevalence is a bit lower (3.6 percent), while in sick cats, it's a bit higher (7.5 percent). The true prevalence of the disease may be underestimated because of the difficulty diagnosing the disorder.

Factors identified as increasing the estimated risk for hemotropic mycoplasmosis were:

Illnesses

Anemia. A finding of anemia increases the chance of the cat having hemotropic mycoplasmosis

FeLV status. A positive correlation exists between feline leukemia virus infection and hemotropic mycoplasmosis

Infrequent vaccination

A history of cat-bite abscesses

Age. There is a higher prevalence in cats less than 3 years old.

Indoor/outdoor status. Free-roaming, outdoor cats are at higher risk.

The mode of transmission in naturally occurring infection has been difficult to elucidate fully. It is believed that hemotropic mycoplasmosis is transmitted by insect vectors, such as fleas, ticks, and mosquitoes, direct contact between cats such as with bite wounds and via blood transfusions. Transmission in utero or by breast milk has been suggested by the detection of the organism soon after birth; intrauterine transmission was suspected when kittens from an infected queen were found to be infected three hours after birth. There are no known risks to humans.

Cats with hemotropic mycoplasmosis experience four phases of disease.

The pre-parasitemic phase. The first phase lasts from 2 to 21 days; during this phase, cats are infected, but don't show clinical signs, and the organism is not detectable in the bloodstream.

The acute phase. The second phase lasts from 2 to 4 months. During this phase, clinical signs occur intermittently, and parasitemia, which is the presence of the organism in the bloodstream, also occur intermittently. Clinical signs vary. Some cats in the acute phase of disease have signs that are so mild that they remain undetected by their owners, while other cats have such severe signs that they may lead to death if left untreated.

The recovery phase. The third phase can vary in duration. Cats can remain mildly anemic, clinical signs are not apparent, and phases of parasitemia are minimal.

The carrier phase. The fourth phase can last for years. Cats appear clinically normal and the organism is rarely detectable in the bloodstream.

Clinical signs and physical exam findings of Mycoplasma haemofelis infection are similar to that seen with other anemias; the severity of the clinical symptoms is related to the magnitude of the anemia, and how quickly that degree of anemia was reached. Pale (possibly yellow tinged) mucous membranes, fever, fatigue, depression, tachypnea (rapid respiratory rate), tachycardia (rapid heart rate), decreased appetite, and enlarged liver and spleen are some of the symptoms that may be observed in cats with hemotropic mycoplasmosis.