Feline Hemotrophic Mycoplasmosis

By Ryan Llera, BSc, DVM; Ernest Ward, DVM

Infectious Diseases, Pet Services

What is feline hemotrophic mycoplasmosis?

Feline hemotrophic mycoplasmosis (FHM) is the name of a relatively uncommon infection of cats. In the past, this disease was called feline infectious anemia or hemobartonellosis. With this disease, the cat's red blood cells are infected by a microscopic blood bacterial parasite. The subsequent destruction of the infected red blood cells results in anemia.

Anemia is a medical term referring to a reduction in the numbers of red blood cells or in the quantity of the hemoglobin, which carries oxygen.

What causes FHM?

FHM is caused by a microscopic bacterial parasite that attaches itself to the surface of the cat's red blood cells. This parasite was recently reclassified and named Mycoplasma haemofelis (it was previously called Hemobartonella felis). The infected blood cells may break down, or they may be treated as ’foreign’ by the cat's immune system and be destroyed. Anemia occurs if enough red blood cells are infected and destroyed.

What are the signs of FHM?

The anemia experienced by a cat may be mild and may not cause any obvious signs. Many cases of FHM infection in cats go undetected. Some of these subclinical cats remain long-term carriers of the disease and spread the disease to other cats. If another disease or condition lowers the cat's immunity, FHM may become clinically evident.

"Many cases of FHM infection in cats go undetected."

If many red blood cells are destroyed, symptomatic anemia occurs. The mucous membranes, readily observed in the conjunctival lining of the eyes and the gums, will be pale to white. If jaundice accompanies the anemia, the membranes may be yellow. Because the oxygen carrying capacity of the blood is decreased, the cat may fatigue quickly, be weak and lethargic, and may lose weight. Additional signs may include fever, an enlarged spleen or lymph nodes, and increased heart and breathing rates.

How is FHM diagnosed?

There are many reasons for a cat to be anemic, and even if M. haemofelis is detected, it may not be the actual cause of the anemia. A full clinical examination with blood and urine tests will be needed to diagnose FHM. Although the blood parasite has a characteristic form on the surface of stained red blood cells, it is a very small organism and can be difficult to observe, especially when relatively few red cells are infected. The proportion of infected cells can fluctuate from day to day.

Because the organism can sometimes be found in normal cats, the mere detection of M. haemofelis does not confirm a diagnosis of FHM, and other possible causes of the anemia should not be overlooked. The test of choice is called a PCR assay which measures a quantitative number of the DNA that corresponds to the organism. Your veterinarian may also recommend an FeLV/FIV test as these conditions are often common with FHM.

Can FHM be treated?

Your veterinarian may prescribe a broad-spectrum antibiotic such as doxycycline, enrofloxacin, or marbofloxacin to treat M. haemofelis infections. In some cases, after an initial good response to antibiotic treatment, there may be a relapse. In addition, the organism can persist in sites protected from the antibiotic. It is important to give the full course of antibiotics to your cat as the antibiotics may not clear the organism if the full treatment is not given. Each antibiotic has its own risk of side effects that your veterinarian will discuss with you.

If another disease is present, it must also be treated. If an immune-mediated disease is suspected, immunosuppressive drugs such as corticosteroids may be used. If the anemia is very severe, a blood transfusion may be required.

How is FHM transmitted and are my other cats at risk?

The major transmission route of FHM is thought to be biting, blood-sucking parasites such as fleas. Direct cat-to-cat transmission or transmission by inanimate objects such as contaminated food bowls and litter-trays seems unlikely. Even if there are other cats in the household, they may remain uninfected, or at least symptom-free. However, a bite from an infected cat may spread the infection or pregnant queens may pass the infection onto their kittens.

The incubation period may be as long as seven weeks although a two-week incubation period is more typical. Due to this long incubation period, the actual source of the infection may be difficult to determine. Since the way it is spread between cats is not fully understood, good hygienic practices should be followed.

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