Bovine Tuberculosis: Borne to be Wild?

Disseminated bovine tuberculosis lesions seen with chronic infection throughout lungs of a wild deer
Disseminated bovine tuberculosis lesions seen with chronic infection throughout lungs of a wild deer. Credits: Deer Alliance

Bovine Tuberculosis (bTB) is generally viewed as a disease of cattle and domesticated bovines. However, there are cycles of spillover of the agent which function in certain niches, especially in peri-sylvatic ecosystems where interactions between domesticated bovines and wild cervids (deer) or other wild bovines (wildbeeste) may create vulnerabilities. Since it is especially difficult to monitor the disease in wild populations, such spillovers may be difficult to detect and have extensive impact before effective interventions are implemented. The identification of bTB in wild cervids in South Eastern Indiana in the United States thus serves as a reminder of this difficult issue.

According to an advisory released by the Indiana State Board of Animal Health, a wild white tailed doe has been diagnosed to be suffering from bovine Tuberculosis (bTB) in Franklin County, Indiana, United States. The animal has been culled at the facility at which it was diagnosed, as is the recommended method to deal with identified diseased animals. This has triggered more intensive disease monitoring in the region, especially targeting cattle owners and deer hunters, who may be at higher risk of contracting and/or spreading this zoonotic infection. This means that the usual three mile radius of surveillance will be expanded to ten miles, since the federal requirements mandate this expansion if bTB is diagnosed in free ranging wildlife. For deer hunters, mandatory sampling and laboratory testing of white tailed deer hunted within specific zones has been instituted.

Between 2008 and 2016, the Indiana State Board of Animal Health has identified four individual cases of TB in three cattle herds and a cervid farm in this region between 2008 and 2016:

2008: Single beef cow trace, with no other positives

2009: Cervid herd found to be positive and depopulated

2010: Two beef traces

2011: Beef herd infected; bears genetic resemblance to the traces identified in 2010

This case presents the interesting and difficult challenges provided by the spillover of infectious agents between domesticated and wild animals. It further strengthens the notion that in countries like India, which do not have mandatory screening and/or robust surveillance systems dedicated to identifying bTB in domestic and wild herds, this is a problem whose burden is yet to be understood completely. Given the difficulties in sampling wild animals, and the absence of surveillance systems in peri-sylvatic environments, it is likely that such spillover cycles for diseases like bTB and brucellosis are active. Further research is needed to identify the burden of such issues.

Image Credit: Deer Alliance.


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