Prolonged persistence of canine distemper virus RNA, and virus isolation in naturally infected shelter dogs.

Canine distemper virus remains an important source of morbidity and mortality in animal shelters. RT-PCR is commonly used to aid diagnosis and has been used to monitor dogs testing positive over time to gauge the end of infectious potential. Many dogs excrete viral RNA for prolonged periods which has complicated disease management. The goal of this retrospective study was to describe the duration and characteristics of viral RNA excretion in shelter dogs with naturally occurring CDV and investigate the relationship between that viral RNA excretion and infectious potential using virus isolation data. Records from 98 different humane organizations with suspect CDV were reviewed. A total of 5,920 dogs were tested with 1,393; 4,452; and 75 found to be positive, negative, or suspect on RT-PCR respectively. The median duration of a positive test was 34 days (n = 325), and 25% (82/325) of the dogs still excreting viral RNA after 62 days of monitoring. Virus isolation was performed in six dogs who were RT-PCR positive for > 60 days. Infectious virus was isolated only within the first two weeks of monitoring at or around the peak viral RNA excretion (as detected by the lowest cycle threshold) reported for each dog. Our findings suggest that peak viral RNA excretion and the days surrounding it might be used as a functional marker to gauge the end of infectious risk. Clarifying the earliest point in time when dogs testing positive for canine distemper by RT-PCR can be considered non-contagious will improve welfare and lifesaving potential of shelters by enabling recovered dogs to be cleared more quickly for live release outcomes.