A new study led by the University of Cambridge and Penn State University has shown that vaccination not only reduces the severity of bovine tuberculosis (TB) in infected cattle but also reduces transmission.
This was the first study to show that Bacillus Calmette-Guérin (BCG) vaccinated cattle infected with TB are “substantially less infectious to other cattle”.
According to researchers the indirect effect of the vaccine “beyond its direct protective effect” had not been measured before.
The study, which was carried out in Ethiopia, examined the BCG vaccine’s ability to directly protect cattle that receive it, as well as to indirectly protect both vaccinated and unvaccinated cattle by reducing TB transmission
Andrew Conlan, associate professor of epidemiology at the University of Cambridge’s Department of Veterinary Medicine and a corresponding author of the study, said researchers 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,” Dr. Conlan added.
The team also developed a transmission model to explore the potential for routine vaccination to control TB.
“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 1, arresting the projected increase in the burden of disease and putting herds on a pathway towards elimination of TB,” Dr. Conlan added.
The reason the team focused their studies in Ethiopia was because it is a country with the largest cattle herd in Africa and a rapidly growing dairy sector.
It also has a growing instance of TB and no current control program in place.
TB
According to Professor James Wood, Alborada Professor of Equine and Farm Animal Science in the University of Cambridge’s Department of Veterinary Medicine, TB is more prevalent in lower-income countries.
But he said that Ireland, New Zealand and the UK also experience considerable economic pressures from the disease which continues to “persist despite intensive and costly control programs”.
Prof. Wood added: “For over twenty-years the UK government has pinned hopes on cattle vaccination for bovine tuberculosis as a solution to reduce the disease and the consequent costs of the controls.
“These results provide important support for the epidemiological benefit that cattle vaccination could have to reduce rates of transmission to and within herds.”
