BCG vaccine TB eradication hope
VACCINATION not only reduces the severity of TB in infected cattle, but reduces its spread in dairy herds by 89%, research finds.
Research by the University of Cambridge and Penn State University found that vaccination significantly increases predictions for the eradication and control of bovine tuberculosis (TB).
This groundbreaking study demonstrates that BCGvaccinated cattle infected with TB exhibit reduced infectiousness to other cattle, signifying a unique indirect effect of the vaccine beyond its primary protective role, which has not been counted previously. The transmission of TB from livestock has been estimated to contribute to approximately 10% of human tuberculosis cases.
While zoonotic TB (zTB) infections are most commonly associated with gastrointestinal conditions stemming from the consumption of contaminated milk, zTB can also prompt chronic lung infections in humans. Lung disease induced by zTB resembles normal tuberculosis but poses greater challenges for treatment due to inherent antibiotic resistance in cattle bacteria.
TB remains prevalent in many countries worldwide, including Europe and America, where its control means substantial costs for farmers and taxpayers.
Published in the journal Science, a study led in Ethiopia investigated the effectiveness of the Bacillus Calmette-Guérin (BCG) vaccine in directly protecting vaccinated cattle and indirectly safeguarding both vaccinated and unvaccinated cattle in reducing TB transmission. Over two years, vaccinated and unvaccinated animals were placed in enclosures with naturally infected animals, engaging a unique crossover design.
Associate professor of epidemiology at the University of Cambridge’s department of veterinary medicine and a corresponding author of the study, Andrew Conlan, said: “Our study found that BCG vaccination reduces TB transmission in cattle by almost 90%. Vaccinated cows also developed significantly fewer visible signs of TB than unvaccinated ones. This suggests that the vaccination not only reduces the progression of the disease, but that if vaccinated animals become infected, they are substantially less infectious to others.”
Developing livestock census and movement data from Ethiopia, the team developed a transmission model to assess the potential of routine vaccination in controlling TB.
He added: “Results of the model suggest that vaccinating calves within the dairy sector of Ethiopia could reduce the reproduction number of the bacterium — the R0 — to below one.”
The study focused on Ethiopia, home to Africa’s largest cattle herd and a rapidly expanding dairy sector, experiencing a growing burden of TB with no existing control program, serving as a model for similarly situated transitional economies.
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, said: “For over 100 years, programmes to eliminate TB have relied on intensive testing and slaughtering of infected animals. 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.”
Professor James Wood, Alborada professor of equine and farm animal science in the university of Cambridge’s department of veterinary medicine, highlighted that despite higher occurrence rates in lower-income countries, the UK, Ireland, and New Zealand also grapple with substantial economic burdens from the disease.
He said: “For over 20 years the, UK Government has pinned hopes on cattle vaccination for TB as a solution to reduce the disease and the consequent costs of the controls. These results provide support for the epidemiological benefit that cattle vaccination could have to reduce rates of transmission to and within herds.”