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.

Antemortem detection of Mycobacterium bovis in nasal swabs from African rhinoceros

“…Previous studies in African buffaloes have reported the high diversity of NTMs present in respiratory samples 23 . A study investigating M. bovis shedding in African wild dogs in KNP described a low percentage of M. bovis positive cultures (3.1–3.5%) of respiratory samples from IGRA positive individuals 17 , like findings in the current study. However, Parsons et al (2017) described a waning in QFT IGRA responses in three M. bovis experimentally infected white rhinoceros over time, with only a low IFNg in vitro response to purified protein derivative of M. avium 19 .…”

“…In a separate study of a human population with culture-confirmed M. tuberculosis infection (n = 80), M. tuberculosis DNA was detected in oral swabs from 29 (36.3%) individuals 36 . In a KNP population of African wild dogs ( Lycaon pictus ) with immunological sensitisation to M. bovis (determined using an IGRA) (n = 136), M. bovis was only recovered by conventional mycobacterial culture in 4 oronasal samples 17 . However, to our knowledge, this is the first report of M. bovis detection in nasal (swab) samples from African rhinoceros.…”

“…In this study, MTBC DNA and/or viable M. bovis were only detected in nasal secretions from study individuals with immunological evidence of infection (IGRA positive), and not from any IGRA negative individuals, which supports the hypothesis that at least some of the IGRA positive individuals were truly infected and may be shedding mycobacteria. This raises concern that M. bovis infected rhinoceros may be a source of exposure for other susceptible animals sharing the environment 15 , 17 , 39 . Inclusion of a larger sample size of IGRA negative rhinoceros in future studies could better inform this hypothesis.…”

Antemortem detection of Mycobacterium bovis in nasal swabs from African rhinoceros

“…tuberculosis DNA was detected in oral swabs from 29 (36.3%) individuals 36 . In a KNP population of African wild dogs (Lycaon pictus) with immunological sensitisation to M. bovis (determined using an IGRA) (n = 136), M. bovis was only recovered by conventional mycobacterial culture in 4 oronasal samples 17 . However, to our knowledge, this is the rst report of M. bovis detection in nasal (swab) samples from African rhinoceros.…”

Comparison of interferon gamma release assay and CXCL9 gene expression assay for the detection of Mycobacterium bovis infection in African lions (Panthera leo)

“…Because of the slow progression of disease, there are significant challenges in early detection of bTB in free-ranging wildlife, since most infected animals can shed viable mycobacteria before manifestation of visible clinical signs (Michel et al, 2006;Meiring et al, 2021). Therefore, to prevent the risk of introducing disease into new populations, movement of animals from endemic areas is restricted, unless there are accurate tests that can be used for screening.…”