HAEMOTROPIC MYCOPLASMA INFECTION IN CATS: A DIAGNOSTIC CHALLENGE

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Haemotropic Mycoplasmas are small rickettsial organisms that can cause severe haemolytic anaemia in cats. In the past, the disease was called feline infectious anaemia or haemobartonellosis but recently the infectious agent has been reclassified and named Mycoplasma haemofelis.

There are three main species that are distributed worldwide, with varying prevalence and associated clinical signs. Mycoplasma haemofelis is the most pathogenic species and acute infection can result in severe haemolytic anaemia. The most common clinical signs in acutely infected ill cats with severe anaemia include tachypnoea, depression, anorexia, weight loss, and pale or icteric mucous membranes. Splenomegaly may also occur.

Candidatus Mycoplasma haemominutum and Candidatus Mycoplasma turicensis have also been described in the cat and commonly cause a chronic, subclinical infection. However, haemolytic anaemia may occur with these species but is mainly associated with concurrent retroviral infections (FeLV, FIV) or other diseases. Unfortunately, these organisms are infrequently observed on blood films owing to their small size.

Blood smear examination. Of all the species, Mycoplasma haemofelis is the one that can be observed more frequently on stained blood smears, because of its size, and mainly during the acute phase of the disease. They appear as rod, coccoid, and ring-shaped structures, found individually or in chains on the surface of red blood cells. Fresh smears are essential to visualise the microorganisms on the membranes of red blood cells, because they tend to detach from erythrocytes during storage in EDTA. Moreover, their identification is commonly left to experienced personnel because false positive may occur due to stain precipitate artefacts, drying artefacts, Howell Jolly bodies, basophilic stippling and siderotic inclusions.

Mycoplasma haemofelis infection, blood smear, cat, Wright Giemsa, 50x.

PCR assays are available and represent the diagnostic test of choice for this disease. Testing is commonly performed on EDTA blood samples and is highly sensitive and specific. A positive result does not always equate with clinical illness, and therefore, PCR results should be interpreted in conjunction with clinical findings. This may occur when organisms are incidentally observed in carrier cats with other diseases.

For more information about this and other PCR testing do not hesitate to contact the laboratory.