The objective of part A of this study was to evaluate the prevalence of subclinical hemotropic Mycoplasma (HM) infection in two distinct feline populations: a local shelter population (SPCA) and a client-owned population. The objective of Part B of this study was to evaluate the inter- and intra-test variability of two independent qualitative PCR assays used for the diagnosis of feline HM infections.
For part A, an EDTA and serum blood sample was collected from 58 SPCA and 57 client-owned cats determined to be healthy based on physical examination. The packed cell volume, total protein, and retroviral status were determined for each cat. In addition, each cat was screened for a subclinical HM infection using a) a qualitative polymerase chain reaction (PCR) assay for the 16S rRNA of Mycoplasma haemofelis and "Candidatus M. haemominutum", and b) cytologic evaluation of a blood smear looking for evidence of hemoplasma organisms.
In part B, blood samples from 44 cats were submitted to a second laboratory for determination of HM infection using another qualitative PCR assay to evaluate intertest variability. The blood samples included 26 samples from part A (6 positives and 20 negatives) and 18 samples from cats with historical clinical or subclinical HM infections. Where sample volume permitted, the PCR testing was repeated (16 of 44 samples at the first laboratory and 40 of 44 samples at the second laboratory) to assess the intratest variability for both PCR assays.
For part A, the prevalence of subclinical HM infection was 12% (7/58) in the SPCA population and 4% (2/57) in the client-owned population. Within the SPCA population, M. haemofelis was found in 5% (3/58) and "Candidatus M. haemominutum" in 7% (4/58) of cats. The two client-owned cats were infected with M. haemofelis. There was no statistically significant difference in the infection rate between the two populations (p=0.16). Across both populations, no risk factors for HM infection were identified (sex, age, neuter status, breed, retroviral status, external parasitism).
For part B, there was substantial agreement between the two independent PCR assays for M. haemofelis (κ=0.601 95%CI 0.32-0.89) as well as for "Candidatus M. haemominutum" (κ=0.70 95%CI 0.40-0.99). Both PCRs performed well with zero intratest variability respectively.
There is no difference in the subclinical HM infection rates between the SPCA and client-owned cat populations evaluated. In using PCR testing for HM infection, results between laboratories show substantial agreement, but not perfect agreement. This highlights the need for continued attention to standardization of PCR testing.