Mortality rates and survival analysis of owned, free-roaming dogs in a resource-limited community, Bushbuckridge, South Africa

Abstract

Canine rabies can be successfully controlled in dogs through mass vaccination. In populations of free-roaming dogs in resource-limited settings, the maintenance of herd immunity through vaccination is challenged by the high population turnover. Understanding and describing mortality in these populations may therefore assist in the control of rabies. The objective of this study was to determine the rates and causes of mortality in owned, free-roaming dogs in Hluvukani village, Bushbuckridge, South Africa, from May 2014 through July 2015.

From the Health and Demographic Surveillance System in Dogs in Hluvukani village, we followed a nested cohort of dogs one year and older over a 12-month period and puppies born to the cohort for 120 days, from May 2014. Deaths were recorded and investigated through verbal autopsy and post-mortem examination. Survival rates from enrolment (adults) or from birth (puppies) were compared using Cox proportional hazard regression models.

Of the cohort of 367 adult dogs (203 males and 164 females), 27 died during the follow-up period. The mortality rate was 78 per 1,000 dog-years in the cohort. Adult females had a shorter survival time from enrolment (mean = 341.7 days) compared to adult males (mean = 356 days; p = 0.05). No difference in survival was detected between age groups. Enrolled litters were 62 and 329 enrolled puppies, 135 died before 120 days of age. Mortality in puppies was high with 2,390 deaths per 1,000 dog-years recorded, and a mean survival time of 60 days. No difference in survival was observed between males and females (p = 0.3). In adults and puppies, causes of death were identified as natural (43%), non-natural (53%) and euthanasia (4%).

Mortality was low in adult dogs, but very high in the puppies. Despite high population turnover through births and deaths, the vaccination coverage was still sufficient to prevent rabies outbreaks in the village.