Zoonotic Tuberculosis: Challenges and Opportunities for Sri Lanka
Zoonotic Tuberculosis: Challenges and Opportunities for Sri Lanka
M. T. L. K. Jayasumana1, Y. H. P. S. N. Kumara1, M. A. Salgadu1, 2, R. R. M. K. K. Wijesundera1, G. S. P. de S. Gunawardena1, C. D. Gamage3, P. G. A. Pushpakumara1, P. A. B. D. Alexander1, B. V. P. Perera4, A. Dangolla1, N. H. Smith5, D. Magana-Arachchi6, A. A. A. W. K. Amarasinghe1, H. R. N. Jinadasa1*

1Faculty of Veterinary Medicine & Animal Science, University of Peradeniya, Sri Lanka
2Melbourne Veterinary School, University of Melbourne, Australia
3Faculty of Medicine, University of Peradeniya, Sri Lanka
4Department of Wildlife Conservation, Sri Lanka
5Animal and Plant Health Agency, Weighbridge, United Kingdom
6National Institute of Fundamental Studies, Sri Lanka

*Corresponding author email: rnjinadasa@vet.pdn.ac.lk

Zoonotic tuberculosis is primarily caused by Mycobacterium bovis. This neglected topical diseases has relatively higher prevalence in developing countries than developed countries. Sri Lanka is a middle-income island nation in the Indian Ocean with a land extent of approximately 65000 km2. Even though Sri Lanka is not among high disease burden countries for human tuberculosis, approximately 11,000 new cases are reported annually. Zoonotic tuberculosis has not been reported among humans in Sri Lanka. This may be due to underreporting as all acid-fast bacilli positive patients are routinely reported as having “bacteriologically confirmed TB” in Sri Lanka. However, we have recently reported the first two confirmed cases of tuberculosis among Sri Lankan elephants caused by M. tuberculosis strains that are similar to East-African-Indian lineage commonly circulating among humans in the country based on MIRU-VNTR typing. Similar findings have been reported from Nepal recently.

Our pioneering work confirmed bovine tuberculosis in Sri Lanka in 2012. Since then we have confirmed 18 fatal cases among Sri Lankan cattle. Most cases (n=15) were reported from Central province, which has most of the largescale dairy farms. Relatively high herd prevalence of reactive cattle was detected in twenty herds from the same province. One cattle carcass was condemned during meat inspection at a municipal abattoir. The affected animal was originating from North Western province. Remaining two cases were reported from a single farm in North Western province. No data is available on any wildlife reservoirs of M. bovis in Sri Lanka.

Genotyping of these 18 M. bovis strains revealed seven distinctive MIRU-VNTR patterns forming four clusters. The largest cluster had 9 strains; followed by three clusters which had two strains each. The remaining were single strains. Strains from Central province and North Western province clustered separately. Strains obtained from same farms shared similar MIRU-VNTR patterns except two cases. All nine strains in the largest cluster originated from two different farms in Central province and shared an identical MIRU-VNTR pattern. These two farms had a shared source of animals in the recent past. Similar results were observed from M. bovis strains originating form shared animal sources in other endemic countries such as Brazil, Tunisia and Mexico and Zambia. Interestingly, two orphan MIRU-VNTR patterns and two clusters each with two M. bovis strains were found in Central province. This indicates the occurrence of high genetic diversity among the circulating M. bovis strains in Sri Lanka and these findings are comparable with the results reported from other endemic countries. Physical distance between Central province and North Western province was reflected in the increased genetic distance between strains from these two provinces similar to previous observations from Mali, Nigeria, Cameroon, Brazil, Spain and South America Chad.

A subsequent preliminary survey undertaken in 2019 identified relatively low incidence of M. bovis infection among cattle processed at two abattoirs at Western and North Central provinces. M. bovis was detected in 5.2% (6/115) of the lung samples by PCR while only one (0.87%) PCR positive sample had a granuloma. Previous prevalence studies from several endemic countries have reported >10% M. bovis in abattoir surveys. Complete cattle movement history records are not maintained by abattoirs in Sri Lanka. Therefore, this BTB incidence does not necessarily indicate actual disease burden in respective provinces. Most of the cattle processed at the abattoir in North Central province were from the free ranging herds that interact with wildlife at the boarders of the forests or even within the national parks These herds pose a potential risk for introducing M. bovis to wildlife or it may be an indication of carrying the infection from an already established wildlife reservoir.

The epidemiology and public health significance of bovine tuberculosis in Sri Lanka still remains largely unknown. A national level control program was initiated by the Department of Animal Production and Health since 2013. However, number of screening tests performed on live cattle in the country is not sufficient and the country lacks mechanism to compensate culled animals, seriously hampering the control efforts.

Rasika Jinadasa PhD

University pf Peradeniya

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