The red cell parasites formerly known as Haemobartonella and Eperythrozoon spp have been reclassified as hemotrophic mycoplasmas (hemoplasmas) based upon strong phylogenetic evidence and their 16S ribosomal RNA gene sequences. The latter form the basis for polymerase chain reaction (PCR) assays used to detect infection. Haemobartonella and Eperythrozoon spp infecting the dog and cat now have been renamed M. haemofelis (Ohio or large form of H. felis), M. haemominutum (California or small form of H. felis), and M. haemocanis (H. canis).

Like other mycoplasmas, hemoplasmas are small epicellular parasites that lack a cell wall and are susceptible to tetracyclines; their circular, double-stranded DNA encodes only those gene products essential for life. The prevalence of hemotrophic mycoplasma infections in anemic cats in the United States is about 25%, and usually involves M. haemo-felis. The organism is also present in </= 8% of cats with fevers with or without concomitant anemia. It is known to survive in blood donor bags for at least 7 days, after which the organisms start to die off.

Nonanemic cats may also be infected, and the organism most commonly involved is M. haemomi-nutum. M. haemofelis infection is present in < 4% of healthy cats. Chronic infections with hemotrophic mycoplasmas may promote myeloproliferative disorders in FeLV-infected cats. M. haemocanis infection in dogs may be a widespread latent disease in kennel-raised dogs, although definitive research is incomplete.

Diseases caused by infection with hemoplasmas range from overt life-threatening hemolytic anemia to subtle chronic anemia, unthriftiness, and infertility. Most cats without other underlying illness are asymptomatic. A few cats have been found to have mild anemia with no other apparent cause that seems to respond to antibiotic treatment. However, these organisms may act as cofactors in the progression of retroviral, neoplastic, and immune-mediated diseases. Field strains may vary in pathogenicity with the vast majority having minimal or no known pathogenic effects.

Intimate contact of hemoplasma organisms with red blood cells leads to cell injury through immune-mediated and other mechanisms that have not yet been defined. Despite an intense immune response and with prolonged antibiotic treatment, infected animals probably remain chronic carriers even after clinical signs have resolved.

Hemoplasma PCR assays are exquisitely sensitive for detection of M. haemofelis and M. haemominutum, and so testing of blood donor cats (and perhaps dogs for M. haemocanis) should be done regularly. Based on PCR screening of healthy blood donor cats, about 20% are infected with M. haemominutum. If the animal is being administered any antibiotic therapy, a 7 d washout period is advised prior to testing.

While fleas may be involved in the transmission of M. haemofelis in cats, the prevalence of infection in flea states (e.g. Florida) and non-flea states (e.g. Colorado) is the same, which suggests that fleas are not an important route of transmission of hemoplasmas. There is some evidence that Rhipicephalis sanguineous is involved with transmission of M. haemocanis to the dog.

Treatment with doxycycline (10 mg/kg q 24 h) effectively controls acute infection in the cat and dog, and enrofloxacin may also be effective in the cat. Doxycycline is well-tolerated by cats if made into a tuna or liver flavored suspension at 25 mg / mL. Initial treatment duration is 7 d. Based on clinical signs of improvement, continue treating for 28 d, although no data exists indicating that 28 d of therapy is necessary.

While cats go transiently PCR-negative during treatment with tetracyclines (but not with quinolones), the organism is typically not able to be eliminated. Asymptomatic cats infected with M. haemominutum do not need to be treated with doxycycline.

Treatment with quinolones generally does not cause PCR tests to revert to negative during therapy. Enrofloxacin (Baytril®) at 5 mg/kg q 24 h is given for a minimum of 7-10 days, but treatment should be continued for 28 days, if feasible. Avoiding light exposure during treatment should reduce the chance of the very rare adverse drug effect of retinal degeneration. Marbofloxacin (Zenequin™) at 2.5-3 mg/kg q 24 h has ben used experimentally for 28 d. After 7 d treatment, cats remained PCR- positive and most were still positive at 28 d. Imidocarb (Imizol®) can be given IV or SC for 14 d for cats difficult to medicate, but results are inconclusive. While the toxicity risk is small, the product stings on administration and some cats hypersalivate.

References: Messick, Vet Clin Pathol 33:2-13. 2004; Messick, Vet Clin N Am 33:1453-1465, 2003; and based on Antech Consultants Conference with Dr. Michael Lappin, Colorado State University, August 2006.