Update on the Diagnosis and Management of Feline Haemoplasmosis

The new names for Haemobartonella felis are Mycoplasma haemofelis (Mhf), ‘Candidatus Mycoplasma haemominutum’ (Mhm), and ‘Candidatus M. turicensis’. Strains evaluated in the United States and the United Kingdom are genetically similar. In the studies of experimentally infected cats performed to date, Mhf is apparently more pathogenic than Mhm; all Mhf inoculated cats became clinical ill whereas Mhm inoculated cats were generally subclinically infected. Cats with chronic Mhm infection had more severe anemia and longer duration of anemia when experimentally infected with Mhf when compared to cats infected with Mhf alone.

Transmission of the Disease

In a recent study, we collected fleas from cats and attempted to amplify hemoplasma DNA from flea digests as well as the blood of the cat. The prevalence rates for Mhf in cats and their fleas were 7.6% and 2.2%, respectively. The prevalence rates for Mhm in cats and their fleas were 20.7% and 23.9%, respectively. In addition, fleas ingest Mhm and Mhf from infected cats when feeding. In one cat, we documented flea feeding to transfer Mhf. However, when we fed Mhf or Mhm infected fleas to cats, infection was not documented. In other studies, hemoplasmas have been transmitted experimentally by IV, IP, and oral inoculation of blood. Clinically ill queens can infect kittens; whether transmission occurs in utero, during parturition, or from nursing has not been determined. Transmission by biting has been hypothesized and the organisms are in the mouths of cats. Red blood cell destruction is due primarily to immune-mediated events; direct injury to red blood cells induced by the organism is minimal.

Symptoms and Diagnosis

Clinical signs of disease depend on the degree of anemia, the stage of infection, and the immune status of infected cats. Coinfection with FeLV can potentiate disease associated with Mhm. Clinical signs and physical examination abnormalities associated with anemia are most common and include pale mucous membranes, depression, inappetence, weakness, and occasionally, icterus and splenomegaly. Fever occurs in some acutely infected cats and may be intermittent in chronically infected cats. Evidence of coexisting disease may be present. Weight loss is common in chronically infected cats. Cats in the chronic phase can be subclinically infected only to have recurrence of clinical disease following periods of stress. The anemia associated with hemoplasmosis is generally macrocytic, normochromic. Chronic non-regenerative anemia is unusual in cats with hemoplasmosis. Neutrophilia and monocytosis have been reported in some hemoplasma-infected cats. Diagnosis is based on demonstration of the organism on the surface of erythrocytes on examination of a thin blood film or PCR assay. Organism numbers fluctuate and so blood film examination can be falsely negative up to 50% of the time.The organism may be difficult to find cytologically, particularly in the chronic phase. Thus, PCR assays are the tests of choice due to sensitivity. Primers are available that amplify a segment of the 16S rRNA gene common to both hemoplasmas. Real time PCR to quantify hemoplasma DNA has now been titrated and can be used to monitor response to treatment. [...]