To vaccinate or not to vaccinate: Lessons learned from an experimental mass vaccination of free-ranging dog populations

Abstract

Domestic animal populations have the potential to act as reservoirs for multi-host pathogens, which may be transmitted to native species and cause population declines or extirpations. Domestic dogs are known reservoirs for several multihost pathogens that may be transmitted to native carnivores. Mass vaccination of dogs has been suggested as a tool for mitigating the disease threat to sympatric carnivores. To determine the extent to which such mass vaccination programs are practicable and appropriate for large, free-ranging dog populations, a vaccination experiment was undertaken in six villages adjoining the Great Indian Bustard Wildlife Sanctuary in central India. Dogs from three villages were vaccinated against rabies virus, canine adenovirus (CAV), canine parvovirus (CPV) and canine distemper virus (CDV) (treatment dogs), while those from three other villages were only vaccinated against rabies virus (control dogs). Immunoglobulin G (IgG) antibody titers against CAV, CPV and CDV in control and treatment dogs were determined on four occasions during the study. When first examined, a large proportion of the initially unvaccinated adult dogs in both the control and treatment group were IgG antibody positive, indicating prior natural exposure. Dogs recovering from natural infection because of CAV, CPV and CDV develop a lifelong immunity and are thus protected against these pathogens. For each of the three viruses, background antibody seroprevalence rates were generally > 72%. Furthermore, several unvaccinated adult dogs acquired protection against these pathogens during the study. Vaccination failed to increase the proportion of adult dogs with IgG antibodies against CAV, CPV or CDV in the treatment group compared with the control group, as much of the effort was put into vaccinating dogs that were already antibody positive. In such situations, vaccination of adult dogs against these enzootic viral pathogens seems unnecessary, and would escalate the cost-benefit ratio of dog disease control programs.