Detection of Canine Distemper Virus RNA From Blood and Conjunctival Swabs Collected From Healthy Puppies After Administration of a Modified Live Vaccine
J.H. Burton; J.K. Veir; L. Pearce; J.R. Hawley; M.R. Lappin
Reverse transcriptase polymerase chain reaction (RT-PCR) assays are now being used to detect canine distemper virus (CDV) RNA in samples from dogs to aid in the clinical diagnosis of infection. However, little information exists on whether administration of modified live CDV containing vaccines affects the test results. The objective of this study was to determine the duration of detectable levels of CDV RNA in blood and conjunctival cells from healthy puppies vaccinated with a modified-live CDV containing vaccine.
Of the 12, six week old puppies selected for study, six were from a bitch with a high CDV antibody titer (1:512) against CDV and six were from a bitch with a low CDV antibody titer (1:64). On day 0, the puppies from the bitch with the high CDV titer were seropositive and the puppies from the bitch with the low CDV titer were seronegative. A modified-live CDV containing vaccine was administered SQ on day 0 and blood and conjunctival swabs were collected on days 0, 2, 5, 7, 10, and 14. Fluorescent antibody (FA) staining of smears made from the conjunctival swabs and a conventional CDV RT-PCR on RNA extracted from whole blood and conjunctival swabs were performed on samples from all time points.
Positive FA test results were detected in one seronegative puppy on day 0, five seronegative puppies and five seropositive puppies on day 2, one seronegative puppy on day 5, and five seronegative puppies and one seropositive puppy on day 10. CDV RNA was not amplified from conjunctival swabs of any puppy on any day. CDV RNA was amplified from blood of three seronegative puppies on day 7.
Current CDV diagnostic test results are not specific for the disease and so positive CDV FA results on conjunctival smears and conventional CDV RT-PCR results on blood should be cautiously interpreted, especially in recently vaccinated, previously naïve dogs.