Mycoplasmas in feline medicine (Proceedings)
Mycoplasma species have been isolated in our laboratory from cats with URTD (Veir et al 2004) and have been detected at a higher rate in cats with URTD than normal cats by other authors (Bannasch and Foley 2005). However, they are readily detected in the oropharynx and nasal cavity of normal cats as well (Randolph et al 1993, Tan et al 1977). In cats with chronic upper respiratory tract disease, Mycoplasma species were cultured from the nasal cavity in sick cats only, although the control group was small (Johnson et al 2005) and a Mycoplasma species was grown in pure culture from the nasal cavity in a retrospective study of the disease (Cape 1992). Mycoplasma species have also been isolated more frequently from the conjunctiva of cat with conjunctivitis as compared to normal controls and conjunctivitis has been induced experimentally with a Mycoplasma species as well, although repeated administration was necessary to produce clinical signs (Haesebrouck et al 1991).
The role of Mycoplasma species as pathogens in lower airway disease in the feline is hotly debated as well, with many authors reporting isolation of mycoplasmas from lower airway samples (Chandler and Lappin 2002, Crisp et al 1987, Foster et al 1998, Foster et al 2004b, Foster et al 2004a), but they are also isolated from normal animals (Padrid et al 1991). Anecdotal reports of response to therapy with doxycycline in cats with pure cultures of Mycoplasma species from the lower airway tract are suggestive that the organisms can be true pathogens. It should be noted, however, this group of organisms is associated with lower respiratory disease in humans, frequently in association with asthma. As very few centers have the ability to measure airway reactivity in cats, it is difficult to determine how many of these anecdotal reports also involve an underlying subclinical case of feline lower airway disease.An additional confounding factor in the debate regarding the role of Mycoplasma species in respiratory disease in cats is the fastidious nature of the organism. Mycoplasma species require rapid transport to a diagnostic facility as they do not survive well outside of the host and special media is required for culture (Johnson et al 2004), therefore, the clinician must specifically request culture of the organism in most facilities. Finally, Mycoplasma species are slow growing, requiring up to a week of culture.
The advent of nucleic acid based detection methods has greatly improved diagnosis in human disease. Mycoplasmal pneumonia is a frequent cause of community acquired pneumonia in humans. However, because of the slow microbiologic culture characteristics, both serology and culture results are evaluated in diagnosis. In a small comparative study, a real-time PCR and a conventional endpoint PCR were shown to be more sensitive than and as specific as traditional serologic diagnosis (Templeton et al 2003) and allows for more targeted therapies earlier in the disease due to decreased turnaround time. The improved sensitivity and turnaround time has also been applied to patients with mycoplasmal pneumonia in order to decrease morbidity associated with sampling techniques. The results of a real-time PCR applied to serum were as specific as traditional diagnostic methods (serology and clinical signs) although not as sensitive (Daxboeck et al 2005). These techniques have been evaluated in the feline species as well. A Mycoplasma felis-specific conventional endpoint PCR was recently developed and evaluated for use in clinical specimens from the respiratory tract of cats (Chalker et al 2004). The PCR assay was both sensitive and specific, allowing for widespread use in veterinary diagnostic laboratories and decreased turnaround time for clinicians awaiting results. Another laboratory applied the results of a conventional endpoint PCR specific for Mycoplasma at the genus level to both nasal flush and biopsy specimens in normal cats and compared the results to microbiologic culture (Johnson et al 2004). Concordance between the two assays was excellent and the more broadly defined amplicon may allow for a more useful screening assay. In our investigation of the organisms associated with URTD in cats, nine cases were identified in which traditional primary pathogens were not detected, either by molecular or microbiological culture techniques, but did have positive samples for Mycoplasma felis. The implication of these findings is still to be determined.