Treatment of Mycoplasma spp. infections in cats - Veterinary Practice
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Treatment of Mycoplasma spp. infections in cats

Mycoplasma spp. are common cell wall deficient bacteria that colonise cats. Some Mycoplasma spp. reside on the surface of mucous membranes and are frequently isolated from the mouth, pharynx, airways and conjunctiva of cats.

While these Mycoplasma spp. are generally non-pathogenic, clinical illness results in some cats. For example, M. felis has been associated with conjunctivitis and rhinitis in cats. Mycoplasma spp. have also been associated with bronchitis and pneumonia in cats.

There are currently three recognised Mycoplasma spp. that are associated with red blood cells of cats: Mycoplasma haemofelis, Candidatus M. haemominutum and Candidatus M. turicensis. These organisms are collectively called haemoplasmas, have been associated with anaemia in cats, and have been amplified from the blood of cats from many countries using polymerase chain assay.

Mycoplasma spp. are resistant to beta lactam antibiotics because they lack a cell wall. Clinical illness resulting from Mycoplasma spp. infection generally responds to administration of drugs in the tetracycline classes. In some cases, however, the organisms are resistant to tetracyclines but susceptible to fluoroquinolones.

The mucous membrane associated Mycoplasma spp. can be cultured, but antibiotic susceptibility testing is difficult and usually not available to general practitioners. The haemoplasmas have never been successfully cultured and so antibiotic susceptibility testing has never been performed. Thus, treatment of Mycoplasma spp. infections of cats is generally empirical.

The following are examples of the use of antibiotics in the management of Mycoplasma spp. infections in cats. Most cats with fever or haemolytic anaemia suspected to be from haemoplasmosis have been administered doxycycline at 10mg/kg, PO, every 12-24 hours for 7 to 28 days. If the hydrochloride salt of doxycycline is used, doxycycline should be administered as a flavoured suspension, given with a liquid, or given within a pill treat to avoid oesophageal discomfort and potential oesophageal inflammation and stricture.

In studies of experimentally infected cats, tetracycline administration can lessen parasitaemia and clinical signs of disease but have not consistently sterilised the blood. In addition, some cats with clinical haemoplasmosis appear to be resistant to administration of tetracyclines. In these cats, administration of antibiotics in the fluoroquinolone class appears to be frequently effective; enrofloxacin was the first drug studied.


The drug was well-tolerated in experimentally infected cats administered 5mg/kg or 10mg/kg, PO, every 24 hours for 14 days. The drug was equally effective or more effective than doxycycline for the treatment of the clinical manifestations of haemoplasmosis in this study.

Administration of enrofloxacin rapidly decreased DNA copy numbers in blood, but some cats are still PCR positive after a course of therapy. Cats administered marbofloxacin also are PCR positive after treatment.

Haemoplasmas are ingested with blood by Ctenocephalides felis which may be a vector. Fleas in the United Kingdom and the United States have been PCR positive for Mycoplasma haemofelis or Candidatus M. haemominutum. Thus, to attempt to prevent transmission of haemoplasma infections among cats, it might be prudent to consistently administer flea control products to cats.

While controlled studies assessing these recommendations are lacking for the haemoplasmas, recent work showed that administration of a combination product containing imidacloprid and moxidectin blocked transmission of Bartonella henselae among research cats. This organism is also erythrocyte associated with C. felis as the vector.

Almost all cats with mucopurulent or purulent nasal discharge have a bacterial component to their disease. In addition, bacterial bronchitis can occur in cats with Bordetella bronchiseptica, Mycoplasma spp. and Chlamydophila felis cited as primary causes.

Studies in humane shelters

We recently completed a study of cats with conjunctivitis and rhinitis housed in humane shelters in two regions of the United States. In that study, the clinically ill cats were more likely to have Mycoplasma spp. DNA amplified from conjunctival cells than healthy kittens housed in the same shelters (p<0.0006) supporting the hypothesis that Mycoplasma spp. of cats can be primary pathogens (Zirofsky, D. and Lappin, M. R., unpublished data).

Veterinarians in the United States frequently administer amoxicillin-clavulanate to cats with mucopurulent rhinitis or suspected bacterial bronchitis and this therapy is often effective. However, as discussed, this class of antibiotic is ineffective for Mycoplasma spp. infections as these organisms do not have a cell wall. Thus, cats with suspected bacterial rhinitis or bronchitis that fail to respond to antibiotics in the beta lactam class should be treated with an alternate drug class that may be effective for Mycoplasma spp.

The author has frequently prescribed doxycycline at 10mg/kg, PO, daily or enrofloxacin at 5mg/kg, PO, daily to cats with mucopurulent rhinitis or bronchitis suspected to be from Mycoplasma spp. infection with clinical success. In addition, most B. bronchiseptica isolates in the United States are susceptible to fluoroquinolones or tetracyclines.

Most cats with acute mucopurulent rhinitis or bacterial bronchitis only need to be treated for 7 to 10 days. Cats with chronic disease may require treatment for several weeks. Many cases of bacterial rhinitis are secondary to other diseases including trauma, neoplasia, inflammation induced by viral infection, foreign bodies, inflammatory polyps, and tooth root abscessation.

Cats with suspected bacterial bronchitis often have an underlying cause like allergic bronchitis. Thus, if routine antibiotic therapy fails, a diagnostic work-up should be performed.


Polyarthritis in cats from Mycoplasma spp. infections is thought to be rare and only a few case studies have been reported. Most cats evaluated at Colorado State University have had fever, exercise intolerance and a stiff gait.

Cytology of synovial fluid reveals non-septic suppurative inflammation and both M. felis and other Mycoplasma spp. have been grown or amplified from affected joints by PCR assay. Doxycycline at 10mg/kg, PO, daily has been clinically effective for the treatment of some cats.

In a recent case treated at Colorado State University, administration of doxycycline failed to sterilise the joints of a cat with M. felis grown and amplified from multiple joints. After administration of enrofloxacin at 5mg/kg, PO, for 28 days, neither the organism nor its DNA were detected on recent joint taps.

Administration of enrofloxacin at high doses has been associated with retinal degeneration in some cats, particularly if significant systemic illness exists and the drug is administered at high doses parenterally.

Experience over the past years indicates that globally, adverse events reporting ocular disorders after use of enrofloxacin in cats administered the label dose are at or below one case in 500,000 treatments. My research group has not recognised enrofloxacin associated retinal disease in cats when enrofloxacin is administered orally at 5mg/kg, PO, daily.

Feline vaccination guidelines available

“FACT sheets”, highlighting the main recommendations of the guidelines issued by the Advisory Board on Cat Diseases (ABCD) – a panel of 17 veterinarians from 10 European countries – are now available online at – in 18 European languages. They can be freely downloaded. They cover feline panleucopaenia, feline herpesvirus infection, feline calicivirus infection, FeLV infection, FIV infection, rabies, feline infectious peritonitis, infections by Chlamydophila felis and Bordetella bronchiseptica. Another gives recommendations on the management of suspected avian influenza in cats.

A full list of references is available on request.

Michael Lappin

Michael R. Lappin, DVM, PhD, DACVIM, graduated from Oklahoma State University in 1981 and completed a rotating internship in small animal medicine and surgery at the University of Georgia. After two years in a small animal practice in Los Angeles, he returned to the University of Georgia where he completed a small animal internal medicine residency and a PhD in parasitology. He was board-certified by the American College of Veterinary Internal Medicine in 1987. He is currently Professor of Small Animal Internal Medicine at the College of Veterinary Medicine and Biomedical Sciences at Colorado State University. Dr Lappin studies feline infectious and immune-mediated diseases and has written over 200 primary research manuscripts and book chapters.

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