Feline Infectious Anaemia

Previously known as: Haemobartonellosis

Caused by: Mycoplasma haemofelis , previously known as Haemobartonella felis

Introduction

Feline Infectious Anaemia, caused by Mycoplasma haemofelis (Mhf), is a regenerative anaemia of cats. The disease occurs worldwide and should be considered as a differential diagnosis for any cat presenting with anaemia.

Aetiology

Mhf is one of a group of organisms known as haemotropic mycoplasmas which infect several other domestic animal species. The causative organism was previously called Haemobartonella felis and thus the disease was known as haemobartonellosis. Polymerase chain reaction (PCR) assays allowing DNA analysis resulted in the reclassification of the organism in 2001. Two other haemotropic mycoplasmas (Candidatus M. haemominutum and Candidatus M. turicensis) have been identified in cats but appear to be less pathogenic.

Mhf can vary in shape from cocci to rods and are sometimes present in chains on the cell surface.

The mode of transmission of Mhf is poorly understood. It is thought that it may be transmitted through biting and fighting activities, although this has not been able to be demonstrated experimentally. As transmission has been shown to occur through blood transfusion, it is recommended that blood donors be screened³.

Signalment

The major group at risk for Mhf infection are young male cats who spend time outdoors. In many areas of the world an association has been shown between Mhf and retroviral infections². It has been demonstrated that cats infected with Mhf and feline leukaemia virus (FeLV) are likely to develop more severe anaemia that cats infected only with Mhf³.

Pathogenesis

The pathogenesis of Mhf is not fully understood. It is thought that the presence of the parasite on the surface of the red blood cells may induce antibody production⁴. The anaemia, which is primarily extravascular, may be due to direct damage of erythrocytes by the organism or as a result of the antibodies produced by the infected animal ².

Clinical signs

Infected cats most commonly present for lethargy and decreased appetite. Physical examination findings are non-specific and can include signs of anaemia, such as mucous membrane pallor, tachypnoea and tachycardia, pyrexia, and occasionally splenomagaly and jaundice. Pyrexia is frequently intermittent and spikes when parasite numbers are highest ³. The anaemia can be severe and rapidly fatal in some cases.

Differential diagnosis

There are multiple causes of both regenerative and non-regenerative anaemia in cats which must be considered as differential diagnoses when investigating a case of an anaemic cats.

For cats showing signs of regeneration, causes of blood loss or haemolysis must be considered:

• primary immune-mediated haemolytic anaemia
• Heinz body haemolytic anaemia (onions, garlic,propofol)
• other infectious causes such as "Babesia felis" and "Cytauxzoon felis"
• neoplasia

Major differential diagnoses for cats with non-regenerative anaemia include:

• neoplasia
• chronic inflammatory conditions
• underlying conditions such as diabetes mellitus and renal disease
• Feline Immunodeficiency Virus (FIV) and FeLV infections
• bone marrow diseases

Diagnosis

The most commmon findings from complete blood counts from cats with Mhf infections are a marcocytic, hypochromic regenerative anaemia. Reticulocytes and Howell-Jolly bodies may be identified on cytologic examination.

Mhf infection can be definitvely diagnosed by identification of organisms on a blood smear, appearing as cocci or rods and sometimes forming short chains of organisms. However, examination of a single blood smear is less than 50% sensitive ⁵ as the animal's immune response causes organisms to disappear from the blood stream for several days, often to reappear a few days later. One study found that smears should be examined every four days over a minimum of three four day cycles⁵, making it possible to have eight days between presentation and diagnosis - clearly not ideal. It also has the potential for misidentification of organisms.

The gold standard for diagnosis of Mhf infection is polymerase chain reaction (PCR), which detects the 16S RNA gene. The test is widely available through veterinary diagnostic laboratories. There are two types of PCR tests; conventional PCR which uses the presence or absence of bands on a gel to assess infection, and real-time PCR assays which uses fluoresence to mark a segment of DNA unique to the organism, making it highly sensitive and species-specific and thus the test of choice. Treatment with antimicrobials may result in false negatives on PCR so collecting before beginning therapy is pereferable.

Treatment

Infected cats should be treated with doxycycline for 3 weeks twice daily. Enrofloxacin is also a good treatment choice especially in refractory cases when combined with doxycycline.

A blood transfusion may also be required in cases of severe anaemia.

As blood sucking endoparasites, such as Fleas, are thought to spread disease the animal should also receive flea treatment.

Prednisolone is also advised to treat the immune mediated mechanisms and to prevent further erythrophagocytosis.

Prognosis

Varied prognosis depending on the severity of the anaemia at presentation. If not treated 1/3 of affected animals will die. Antibiotics do not clear the infection so many cats become carriers of the organism however relapses are uncommon.

References

1. Niemark H, Johansson KE, Rikihisa Y, et al (2001) Proposal to transfer some members of the genera Haemobartonella and Eperythrozoon to the genus Mycoplasma with descriptions of Candidatus Mycoplasma haemofelis, Candidatus Mycoplasma haemomuris, Candidatus Mycoplasma haemosuis and Candidatus Mycoplasma wenyonii Int J Sys Evol Microbiol 51(3) pp891-9
2. Sykes, JE (2010) Feline Hemotropic Mycoplasmas Vet Clinics of North America: Small Animal Practice pp. 1157-1170
3. Wardrop J, Reine N, Birkenheuer A et al (2005) Canine and feline blood donor screening for infectious disease J Vet Intern Med 19(1) pp.135-42
4. Hagiwara, MK (2009) Anemia in Cats: Is It Mycoplasma? Proceedings of the 34th World Small Animal Veterinary Congress
5. Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2)W.B. Saunders Company
6. Czerski A, Gnus J, Agnieszka Rusiecka A, et al (2009) Usefulness of blood films for the feline infectious anaemia diagnosis Acta Sci. Pol., Medicina Veterinaria 9(4)pp. 21-28

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial