A disease that causes many problems in Hong Kong is Feline Infectious Anaemia. This is an often-fatal disease of red blood cells (RBC). There are three different causes of this disease, although only one is present in Hong Kong. In the USA and South Africa certain protozoa, Babesia and Cytauxzoon, are causes, but here a bacteria, Haemobartonella felis, cause it.

Haemobartonella is a member of the Mycoplasma group of bacteria, which are small, primitive bacteria without a cell wall. Two strains exist, with some variation in symptoms depending on which one infects the cat. These bacteria attach themselves to the RBC. They can only grow in cat’s blood, and cannot be cultured, or survive outside of blood. The RBC are damaged by the bacteria, which cause them to rupture. The body also produces antibodies against the damaged RBC. These antibodies may also attack healthy RBC. RBC with antibodies are removed by the immune system. This leads to severe anaemia. The blood loss follows a pattern: RBC with bacteria appear for 1-2 days, followed by a period of about 6 days during which the blood is cleared of bacteria by the immune system.

Cats which recover from the infection will still have bacteria present, possibly lifelong. Generally these cats have low levels of bacteria, and the body can produce RBC as rapidly as the bacteria damage them, so that no symptoms are noticed. The symptoms can recur again, though, if the balance is lost – for instance, if the cat is stressed, has another disease or has drug suppressing the immune system. It is clear, therefore, that, as with many serious diseases, the role of the cat’s immune system in causing serious symptoms is very important. In Europe and the USA almost 50% of all cases involve cats with Feline Leukemia Virus or Feline Immunodeficiency Virus (Cat AIDS). Most cases we see in Hong Kong are after serious disease or major surgery.

The method of transmission of the disease is not well understood, as the bacteria are only found in the blood. Kittens can already get the bacteria from their mothers, either in the uterus or possibly through milk. Blood transfusions or cats swallowing blood can transmit the disease. It is also thought that blood-sucking insects, such as fleas, transmit the disease. Catfights may also be a source. Once a cat has the disease it probably does not cause problems immediately – stress or illness are usually needed to trigger the symptoms.

Symptoms are poor appetite, weight loss and depression, with fevers every few days and pale mucous membranes. Symptoms are often missed initially or interpreted as signs of the illness that ‘triggered’ the FIA. Most cats are diagnosed only in the late stage of disease. To confirm diagnosis, an experienced veterinarian may identify the bacteria on a blood smear, though they are easily confused with other RBC changes. Testing for bacterial DNA is available, but not in Hong Kong at present.

Any cat, which has anaemia of unexplained cause, should be treated for FIA, as blood smear will only be positive during the 1-2 day period, then negative for 6 days. Treatment is often difficult and long courses of antibiotics are needed. Many antibiotics attack bacterial cell walls and are therefore not effective against Mycoplasmas. At present 2 groups of antibiotics, Tetracyclines and Fluoroquinolones, have had effect. Both groups have potential side effects, especially at the high doses needed. Several other drugs have been used, but often with poor success. Corticosteriods can help to reduce blood loss, by ‘switching off’ the immune system and slowing down the blood loss to give the antibiotics more time to have effect. In our experience, response to treatment is slow. Often several different drugs must be tried, and this can be frustrating to owners. Most cases have happy endings eventually, however.

To prevent this disease, cats should be kept as stress free as possible.. Not too many cats should be kept in a household as this causes social stress. Male cats should be neutered to prevent fighting. Vaccinations should be kept up to date, and careful attention paid to flea control, to prevent ‘trigger’ diseases, or opportunities for transmission.