PCR test results for eye infections in shelter cats

Abstract

Signs of ocular infections like discharge and conjunctivitis occur commonly in cats in shelters and feline herpesvirus 1 (FHV-1), Chlamydia felis, Mycoplasma spp, and feline calicivirus (FCV) are thought to be the most common causes. While molecular assays are available to amplify nucleic acids of each of these agents as single tests or in panels, additional information is needed concerning whether the assay results can be used to predict response to treatment. The objectives of this study were to report results for conventional polymerase chain reaction (PCR) assays that amplify nucleic acids of FHV-1, Mycoplasma spp., C. felis, and FCV from cats with signs of acute ocular and upper respiratory infections in an animal shelter and to determine whether the results are associated with treatment responses to topical administration of cidofovir (anti-FHV-1) or oxytetracycline (anti-Mycoplasma spp. and C. felis). Conjunctival samples were collected from both eyes of 60 cats with ocular signs of disease. Total deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) were extracted from each sample and assayed for DNA of FHV-1, Mycoplasma spp., and C. felis and RNA of FCV by conventional PCR assays. Cats were randomized to be administered either oxytetracycline ointment or cidofovir drops in both eyes and a standardized ocular disease score system was used to determine a total ocular score for each cat prior to treatment on Day 0 and on Day 7. Nucleic acids of one or more agents were amplified from one or both eyes from 39 of 60 cats (65%). FHV-1 DNA (21 cats), Mycoplasma spp. DNA (25 cats) or FCV RNA (2 cats) were amplified most commonly. After treatment for 7 days, 32 of 60 cats (53.3%) were considered improved with 27 of 32 cats (84.4%) having ocular scores of 0 (21 cats) or 1 (6 cats). When the results of the FHV-1 PCR assay were compared to cidofovir treatment responses, the positive and negative predictive values of the assay were shown to be 29.4% and 60%, respectively. When the results of the Mycoplasma spp. PCR assay were compared to oxytetracycline treatment responses, the positive and negative predictive values of the assay were shown to be 40% and 38.5%, respectively. The predictive value of conventional PCR assay results for FHV-1 or Mycoplasma spp. DNA was low, suggesting that performing these tests to formulate a treatment protocol has minimal clinical utility in cats with suspected acute ocular infections.