Feline Infectious Anaemia (Haemoplasmosis)

Feline infectious anaemia, known in veterinary medicine as haemoplasmosis, is caused by tiny bacteria that live on the surface of red blood cells rather than inside a wound or organ. The principal culprit is Mycoplasma haemofelis. Once these organisms coat a red blood cell, the cat's own immune system recognises the cell as abnormal and removes it — so the anaemia is really the body destroying its own blood in an attempt to clear the infection.

The severity varies enormously. A healthy adult cat with a competent immune system may fight off a mild infection with only vague, transient illness. But in a kitten, a stressed cat, or — most importantly — a cat already infected with feline leukaemia virus (FeLV) or feline immunodeficiency virus (FIV), the same organism can cause life-threatening anaemia. This is why testing anaemic cats for the retroviruses is routine.

Owners typically notice a cat that has become quiet, weak and reluctant to move, with pale rather than healthy pink gums. Because anaemic blood carries less oxygen, the cat breathes faster and its heart races to compensate. Some cats spike intermittent fevers as the organism periodically multiplies. In the worst cases, the rapid breakdown of red cells overwhelms the liver and the cat becomes jaundiced.

Diagnosis can be tricky, because the bacteria detach from the red cells in cycles and may be invisible on a given blood smear; PCR testing is more reliable. Treatment with doxycycline over several weeks reduces the infection, and steroids may be used to calm the immune destruction of red cells. Many cats recover well, though some become long-term carriers, which is another reason flea control and neutering matter so much.