Offering hope to India where bovine tuberculosis (bTB) poses a significant challenge for the livestock, a study has said that vaccine Bacillus Calmette-Guérin (BCG) used for the infectious disease for humans can significantly reduce infectiousness of vaccinated livestock and improve prospects for its elimination and control.
Bovine tuberculosis (bTB) is a livestock disease that results in large economic losses to animal agriculture worldwide. The disease can also transmit to humans and cause severe illness and death.
With an estimated prevalence of 7.3 per cent among cattle, approximately 21.8 million animals are affected by bTB in India. The burden is expected to escalate in the coming years due to factors such as the rapid intensification of the dairy industry and advancements in cattle rearing methods, according to reports.
“For over a hundred years, programs to eliminate bovine tuberculosis have relied on intensive testing and slaughtering of infected animals,” said Vivek Kapur, professor of microbiology and infectious diseases and Huck Distinguished Chair in Global Health at Penn State and a corresponding author of the study.
“This approach is unimplementable in many parts of the world for economic and social reasons, resulting in considerable animal suffering and economic losses from lost productivity, alongside an increased risk of spillover of infection to humans. By vaccinating cattle, we hope to be able to protect both cattle and humans from the consequences of this devastating disease.”
In the study, carried out in Ethiopia, the researchers examined the ability of the vaccine, Bacillus Calmette-Guérin (BCG), to directly protect cattle that receive it, as well as to indirectly protect both vaccinated and unvaccinated cattle by reducing transmission. They placed vaccinated and unvaccinated animals into enclosures with naturally infected animals in a novel crossover design performed over two years.
“Our study found that BCG vaccination reduces TB transmission in cattle by almost 90 per cent,” said Andrew Conlan, associate professor of epidemiology at the University of Cambridge and a corresponding author of the study. “Vaccinated cows also developed significantly fewer visible signs of TB than unvaccinated ones. This suggests that the vaccine not only reduces the progression of the disease, but that if vaccinated animals become infected, they are also substantially less infectious to others.”
Worldwide, the spillover of infection from livestock has been estimated to account for about 10% of human tuberculosis cases. While such zoonotic TB (zTB) infections are most commonly associated with gastrointestinal infections related to drinking contaminated milk, zTB can also cause chronic lung infections in humans. Lung disease caused by zTB can be indistinguishable from regular tuberculosis but is more difficult to treat due to natural antibiotic resistance in the cattle bacteria.
