Feline infectious anaemia (FIA) is the term used to describe a disease caused by a group of specialised bacteria (called mycoplasmas) that infect red blood cells in the circulation. These bacteria or mycoplasmas are collectively known as 'haemoplasmas'.
Haemoplasmas live on the surface of red blood cells (RBCs) and can sometimes invade the cell itself. By attaching to the surface of the RBC, they damage it, which can result in its destruction (a process known as haemolysis, or literally red cell death). If enough RBCs are destroyed, anaemia develops. The cat's own immune system may be partly responsible for destroying the infected RBCs as it tries to eliminate the organism attached to them.
Clinical signs in affected cats usually reflect the underlying anaemia and include weakness, pallor, a fast heart rate and rapid breathing. Cats which have been infected with haemoplasmas may remain carriers of the organism for long periods, and possibly for life.
The cause of feline infectious anaemia
At least three different haemoplasma species have been identified in cats and these are called:
- Mycoplasma haemofelis
- Mycoplasma haemominutum, and
- Mycoplasma turicensis.
However, these three haemoplasma species have differing abilities to cause clinical disease. Of the three, M haemofelis infection is the most likely to cause severe anaemia , while the other two M haemominutum and M turicensis are more likely to be found incidentally (not causing any disease) or causing more mild anaemia. Even with M haemofelis, many infected cats may not necessarily develop anaemia, but it may be more likely if the cat's immune system is compromised in any way (for example infection with feline leukaemia virus (FeLV) or feline immunodeficiency virus (FIV).
Which cats are at risk?
Mycoplasma heamominutum is generally seen more commonly than the other haemoplasmas but is mostly found in apparently healthy cats. Mycopalsma haemofelis is less common, but more likely to be associated with the development of clinical disease (anaemia).
Adult male cats with access outdoors are more likely to be infected, and fighting is believed to be one of the ways that the organism may be transmitted between cats (the bacteria can be found in the mouth of infected cats so direct transmission through bite wounds is thought to be possible). Fleas may also be able to transmit infection between cats, but while fleas can certainly carry haemoplasmas, it is not certain how easily infection can be transmitted this way
In general, while M haemofelis may be able to cause anaemia in otherwise normal healthy cats, M haemominutum may be more of an opportunistic pathogen, being more likely to cause disease only in cats which are stressed or ill due to other diseases.
Signs of heamoplasma infection
Infections, particularly due to M haemofelis may cause anaemia which may be accompanied by fever in the early stages. Clinical signs of anaemia include tiredness, lethargy, weakness, a reduced appetite, and pale gums (pallor). Weight loss can occur and some cats show increased respiratory (breathing) rate and an increased heart rate.
These signs can be seen with a variety of diseases that cause anaemia, and are not specific for haemoplasma infections.
The best diagnostic test for haemoplasma is a blood test known as PCR (polymerase chain reaction) - this is a molecular test which detects the genetic material (DNA) of the organism in blood samples. It is a very sensitive test and also allows identification of the different haemoplasma species.
Specially stained blood smears can also be examined microscopically to look for the organism on the surface of red blood cells, but this is very unreliable as the organism is not always present in blood smears and also artefacts on the blood smear may be mistakenly identified as organisms
The anaemia induced by feline haemoplasmas is usually regenerative (i.e., the bone marrow will be producing new red blood cells to replace those that are lost). However, not all infected cats develop anaemia. Infected cats should be checked for the presence of underlying illnesses, including FeLV and FIV infection, which may exacerbate haemoplasma infections.
Antibiotics are used to treat haemoplasma infections. Doxycycline has been most commonly used and is given daily for three to four weeks in most cases. Some forms of this drug can cause irritation of the oesophagus (eg,if the tablet is not completely swallowed), so it is important that the cat eats some food or swallows a little water (e.g., 3-5 ml of water syringed into the cat's mouth) after giving the tablet.
Other antibiotics may also be used to treat haemoplasmas but most are not as effective as doxycycline. Pradofloxacin is a relatively new antibiotic that also seems effective.
Corticosteroids may sometimes be used along with antibiotics to suppress any immune-mediated destruction of red blood cells. However, this is probably best reserved for cats that do not respond to antibiotics alone. The PCR test can be used to monitor response of treatment if desired.
In cats with severe anaemia, blood transfusions may be required. Supportive care to encourage the cat to eat, and rehydration therapy in dehydrated cases, are also important.
Although antibiotics can be effective at treating the anaemia with haemoplasma infections, they may not always completely eliminate the organisms. Many cats can remain chronic carriers for months or years. Such carrier cats often appear completely healthy without clinical signs, but relapses (recurrent anaemia) are occasionally reported at times of stress.
Since the methods of transmission of feline haemoplasmas are not fully understood, it is hard to advise on prevention of infection. However in view of the known risk factors which exist for infection, it is wise to take measures to prevent flea infestation and reduce inter-cat aggression by having cats neutered. Infected cats should not be used as blood donors.