Pet Factsheets

Feline Infectious Anemia (FIA)

Feline infectious anaemia, also known as FIA, is an anaemia in cats caused by a blood-borne bacterial infection. 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.

What causes infectious anaemia?

There are a number of infectious diseases (eg Babesia felis in South Africa, feline leukaemia virus) that can result in anaemia in the cat, but FIA typically refers to anaemia caused by the parasites called haemoplasmas. Haemoplasmas are bacteria that live on the surface of red blood cells. Haemoplasmas reduce the lifespan of parasitised red blood cells by damaging the red blood cell surface either causing cell rupture, or marking them for early destruction. As numbers of circulating red blood cells drop, anaemia develops.

Several different species of haemoplasma infect cats: Mycoplasma haemofelis is most frequently associated with severe, life-threatening anaemia; Candidatus Mycoplasma haemominutum, the most common feline haemoplasma, rarely causes clinical anaemia in the absence of other diseases; Candidatus Mycoplasma turicensis can cause anaemia in some cats. All haemoplasmas can cause persistent infection.

How is disease spread?

Being male with outdoor access and having a history of cat fight injuries are risk factors for haemoplasma infection; however, the common routes by which hemoplasmas are naturally spread between cats have not been determined. Fleas are suspected to play a role, at least in some cases, but experimental studies have not provided strong support that this is a common route. Ticks are thought to provide a common route of haemoplasmas transmission in dogs, and feline haemoplasmas have been detected in ticks; however, experimental studies into the role of ticks in the transmission of haemoplasmas in cats have not been performed.

Cat bites injuries may transmit infection, since haemoplasmas are found in the saliva, but transmission this way isn’t always thought to be very effective. Vertical transmission from infected queen to her kittens is also suspected to occur. Transfusion of infected blood can also spread infection.

Cats may be at increased risk of getting anaemia due to haemoplasma infection if their immune response is impaired. This can occur in cats that are ill with other diseases including infections (eg with viruses like FeLV and FIV) and cancer (either due to the cancer or the drugs used to treat it).

How would I know if my cat has infectious anaemia?

Cats are very good at hiding signs of illness, 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 – but these signs are frequently seen in sick cats that are not anaemic. Their gums and ocular conjunctiva 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 after minimal exercise. Cats with infectious anaemia often have a high temperature (fever), and they can become very dehydrated as they stop eating and drinking.

The absence of anaemia does not rule out infection with haemoplasmas as many cats can be infected with them without being anaemic.

How would my vet know that my cat has infectious anaemia?

Your vet may become suspicious that your cat is anaemic from their examination. It will be necessary to take blood samples to confirm the presence and assess the severity of the anaemia. If anaemia is confirmed then further tests, such as X-rays and ultrasound, may be required to look for other possible causes. Further samples of blood may need to be sent away to get final confirmation of the presence of haemoplasmas in the blood. Because of the association between FIA and other diseases such as cancer and FeLV/FIV your vet may want to do other tests to find out if any of these conditions is present in your cat.

How can infectious anaemia be treated?

If your cat is very severely anaemic, they may need to be hospitalised for emergency treatment such as a blood transfusion, intravenous fluids and/or nutritional support. Cats may be started on specific treatment for haemoplasmas whilst waiting for results to come back. Haemoplasmas can only be killed by specific types of antibiotics. Cats with FIA usually show a rapid response to treatment in terms of improvement in clinical signs (a few days), but clinical cure is often not achieved. Generally, the outlook for your cat is good if they do not have any underlying diseases.

If my cat has been treated will they be immune to disease again?

Unfortunately, infection persists in some cats despite long courses of antibiotics, but they usually don’t show any signs of disease; these are called carrier cats. 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. Cats that have a history of FIA should not be used as blood donors, even if they appear normal and haemoplasmas can no longer be detected in their blood.

In cats infected with Mycoplasma haemofelis, the haemoplasma that usually causes the most severe form of FIA, a longer course of treatment can be considered to maximise the chance of cure. However, this involves up to 8 weeks of combination antibiotics and blood monitoring. It is unclear whether it is necessary to completely clear infection.

It is important to control fleas (and ideally ticks) in all cats, as fleas are suspected to be involved in transmission. Neutering cats and limiting their outdoor access will also reduce their risk of becoming infected.