Shedding of Mycobacterium bovis in respiratory secretions of free-ranging wild dogs (Lycaon pictus): Implications for intraspecies transmission.

Abstract

It has recently been discovered that Mycobacterium bovis (M.bovis) causes disease in the endangered African wild dog (Lycaon pictus) in areas endemic for bovine tuberculosis (bTB), including the Kruger National Park (KNP). However, information on M.bovis infection dynamics within this species is limited and requires investigation as M.bovis can cause conservation consequences due to movement restrictions, crucial for genetic management. This study had two aims: firstly, to investigate mycobacterial shedding in free-ranging wild dogs from KNP by culturing oropharyngeal swab (OS) and bronchoalveolar lavage (BAL) samples. Secondly, to determine the relationship between ante-mortem culture and interferon gamma release assay (IGRA) results as well as agreement between OS culture and BAL culture results. Mycobacterial culture revealed that 6 of 173 (3.5%) OS samples and 1 of 32 (3.1%) BAL samples (from 7 different wild dogs) were M.bovis culture positive, suggesting that wild dogs can shed M.bovis through respiratory secretions. However, the possibility of contamination by ingestion of infected prey cannot be excluded in wild dogs with positive OS culture results. Furthermore, the test outcomes between IGRA and culture (OS and BAL) differed substantially. Samples from 172 wild dogs were available for IGRA screening and 134 had positive results (detectable M. bovis immune sensitization). Seven wild dogs had culture-positive results, which included one additional wild dog that did not have an IGRA result (total 173 wild dogs). Out of these 7 M. bovis culture-positive wild dogs, 3 were IGRA positive initially, however, after repeat sampling and testing, 5 out of 7 were IGRA positive. These findings suggest that intraspecies transmission of M.bovis may be possible among wild dogs. Although the risk of intraspecies transmission is currently unknown, this knowledge is important for assessing the risk of M.bovis transmission from infected wild dogs to uninfected populations during translocations.