BCG vaccine reduces spread of TB in cattle, study finds

A tuberculosis vaccine commonly used in humans may also help eliminate the disease in cattle by reducing its spread among animals, a new study has found.

Researchers who vaccinated dairy cows in a field trial in Ethiopia with the Bacillus Calmette-Guérin (BCG) vaccine found it reduced transmission of the disease by 89%.

Field trials of the BCG vaccine and a new diagnostic test to tackle bovine TB are in progress in England and Wales.

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The results of the Ethiopian trials raise hopes that the UK trials can deliver positive results.

However, critics have pointed out that the Ethiopian study was carried out in different conditions, and there is no complication of wildlife infection in that country.

The study in Ethiopia, led by the University of Cambridge and Penn State University and published in the journal Science (PDF), is the first to show that BCG-vaccinated cattle infected with TB are substantially less infectious to other cattle.

Researchers examined the ability of the BCG vaccine to directly protect cattle that receive it, as well as to indirectly protect both vaccinated and unvaccinated cattle by reducing TB transmission.

Vaccinated and unvaccinated animals were put into enclosures with naturally infected animals, in a novel crossover design performed over two years.

Study author Andrew Conlan, associate professor of epidemiology at Cambridge University’s Department of Veterinary Medicine, 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.”

20-year quest

Prof James Wood, head of the department, added: “For more than 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.

“These results provide important support for the epidemiological benefit that cattle vaccination could have to reduce rates of transmission to and within herds.”