Vaccinating cows against TB not only reduces the severity of the infection but reduces its spread in dairy herds by 89 per cent, research has found.
The study, led by the University of Cambridge and Penn State University, is the first to show that BCG-vaccinated cattle infected with TB are substantially less infectious to other cattle.
This indirect effect of the vaccine beyond its direct protective effect has not been measured before.
Around 10 per cent of human TB cases are caught from livestock. The study, published in the journal Science, was carried out in Ethiopia.
Andrew Conlan, associate professor of epidemiology at the University of Cambridge’s Department of Veterinary Medicine, said: “Our study found that BCG vaccination reduces TB transmission in cattle by almost 90 per cent.
“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.”
The team used livestock census and movement data from Ethiopia to develop a transmission model and explore the potential for routine vaccination to control bovine tuberculosis.
“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,” said Prof Conlan.
Ethiopia has the largest cattle herd in Africa and a rapidly growing dairy sector with a growing bovine tuberculosis problem and no current control program.
“Bovine tuberculosis is largely uncontrolled in low- and middle-income countries, including Ethiopia,” said Abebe Fromsa, associate professor of agriculture and veterinary medicine at Addis Ababa University in Ethiopia and the study’s co-lead author. “Vaccination of cattle has the potential to provide significant benefits in these regions.”
“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, published in Science.
“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.”
Prof James Wood, Alborada professor of equine and farm animal science in the University of Cambridge’s Department of Veterinary Medicine, said that despite TB being more prevalent in lower-income countries, the United Kingdom, Ireland and New Zealand also experience considerable economic pressures from the disease, which persists despite intensive and costly control programmes.
“For over 20 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,” said Prof Wood. “These results provide important support for the epidemiological benefit that cattle vaccination could have to reduce rates of transmission to and within herds.”
This research was supported by The Bill & Melinda Gates Foundation, the Biotechnology and Biological Sciences Research Council, the Foreign, Commonwealth and Development Office the Economic & Social Research Council, the Medical Research Council, the Natural Environment Research Council and Defence Science & Technology.
