Feline infectious anaemia, also known as FIA, is an anaemia in cats that is caused by a parasite that lives in the blood. If your cat is unwell and pale, it may be that it is anaemic, but there are many different causes of anaemia in cats and FIA is just one of these. Early recognition and treatment of FIA is important to maximise the chances of full recovery.
There are a number of infections (e.g. Babesia felis in South Africa) that can result in anaemia in the cat, but FIA typically refers to anaemia caused by parasites called ‘haemoplasmas’.
Haemoplasmas are bacteria that live on the surface of red blood cells. Several different haemoplasma species infect cats. Mycoplasma haemofelis (also called the large strain) is the most important haemoplasma as it causes the most severe anaemia in cats. Other haemoplasma species tend to cause less disease in cats: ‘Candidatus Mycoplasma haemominutum’ (also called the small strain) and ‘Candidatus Mycoplasma turicensis’.
When the red blood cell is infected with the haemoplasma parasite it does not survive long in the circulation. The parasite can cause damage to the membrane surrounding the red cell, causing the cell to rupture. Affected blood cells may also be destroyed by the body and, as numbers of circulating red blood cells drop, anaemia develops.
The natural method of haemoplasma transmission has not yet been proven. Fleas are thought to be able to spread infection, so flea bites may transmit infection to your cat. Infected blood transfusions have also been found to spread infection.
It may be that aggressive cat bites transmit infection since haemoplasmas are found in the saliva, but transmission this way isn’t always thought to be very effective. It is known that male cats are more likely to be affected than females which may be the result of their lifestyle and increased risk of fighting. Very young kittens can be infected from contact with their infected mother.
Cats may be more at risk of getting anaemia due to haemoplasma infection if their immune response is reduced. This can occur in cats that are ill with other diseases or cancer. Some drugs (e.g. treatments for cancer) and infections like FeLV and FIV also suppress the immune response and can put cats more at risk from infectious anaemia.
Cats are very good at hiding signs of illness, especially anaemia, so it is possible that you won’t recognise signs of anaemia in your cat until the anaemia is very severe.
Cats with anaemia are generally depressed, lethargic and their appetite may be reduced. The membranes inside their mouth and eyes may appear paler than normal, or sometimes these membranes and the eyes take on a yellowish tinge due to jaundice (as a result of excessive red cell breakdown).
Severely affected cats may have breathing problems and become breathless even after minimal exercise. Cats with infectious anaemia often have a high temperature too, and they often become quite markedly dehydrated as they stop eating and drinking.
Your vet will examine your cat and may be suspicious that it is anaemic from the examination. It will be necessary to take blood samples to confirm the anaemia. If anaemia is found then further tests, such as X-rays and ultrasound, may be required to look for possible causes of anaemia.
Further samples of blood may need to be sent away to get final confirmation of the presence of haemoplasma parasites in the blood. Because of the association between infectious anaemia and other disease such as cancer and FeLV/FIV your vet will probably also want to do other tests to find out if any of these conditions is present in your cat.
The parasites can be killed with antibiotics. Cats usually show quite a rapid response to treatment in terms of improvement in clinical signs, but a longer course (up to 8 weeks) of antibiotics may be required to try and maximise the chances of your cat getting rid of the infection completely.
Additionally, if your cat is very severely affected with profound anaemia, they may need to be hospitalised for emergency treatment such as a blood transfusion, intravenous fluids and/or nutritional support.
Unfortunately infection persists in some cats despite long courses of antibiotics, but they usually don’t show any signs of disease; these cats are called carrier cats. Longer antibiotic treatment courses try to eliminate this carrier status, but it is not always possible.
Following treatment your cat may appear to be quite well again but there is always the potential for a stressful trigger to result in the disease returning in carrier cats, although this is probably not that common.
It is important to control fleas in all cats as fleas are thought to be involved in transmission. Generally the outlook for your cat is good if they do not have any underlying diseases.