Mycoplasma species infections
The large and small forms of Haemobartonella felis are gram-negative, epicellular parasites of feline erythrocytes that have been reclassified as mycoplasmas. The new name
for the large form (Ohio isolate) is Mycoplasma haemofelis.30 The proposed name for the small form (California isolate) is 'Candidatus Mycoplasma haemominutum.'31 Strains evaluated in the United States and the United Kingdom are genetically similar.32 A potentially pathogenic, genetically distinct strain was recently amplified from a clinically ill cat in Switzerland.33 In at least two studies of experimentally infected cats, M. haemofelis was apparently more pathogenic than 'Candidatus M. haemominutum'; all M. haemofelis-inoculated cats became clinically ill, whereas 'Candidatus M. haemominutum'-inoculated cats were generally subclinical.34, 35 Cats with chronic 'Candidatus M. haemominutum' infection had more severe and longer durations of anemia when experimentally infected with M. haemofelis than cats infected with M. haemofelis alone.35
In a recent study, we collected fleas from cats and attempted to amplify Mycoplasma species DNA from flea digests as well as cat blood (Lappin MR, Unpublished data, 2005). The prevalence rates for M. haemofelis infection in cats and their fleas were 7.6% and 2.2%, respectively. The prevalence rates for 'Candidatus M. haemominutum' infection in cats and their fleas were 20.7% and 23.9%, respectively. In addition, fleas ingest 'Candidatus M. haemominutum' and M. haemofelis from infected cats when feeding.17, 18 In one cat, flea feeding was documented as transferring M. haemofelis. In other studies, Mycoplasma species have been transmitted experimentally by intravenous, intraperitoneal, and oral inoculation of blood.36 Clinically ill queens can infect kittens whether transmission occurs in utero, during parturition, or during nursing. Transmission
by biting has been hypothesized. Red blood cell destruction is due primarily to immune-mediated events; organism-induced direct
injury to red blood cells is minimal.
Clinical signs of disease depend on the degree of anemia, the stage of infection, and the immune status of infected cats.36-38 Coinfection with FeLV can potentiate disease associated with 'Candidatus M. haemominutum'.38 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 suffer recurrences following
periods of stress.