UK scientists have developed a novel vaccine and complementary skin test which could stop the spread of bovine TB.
For the first time a vaccine has been created that is compatible with a synthetic form of the tuberculin skin test (PPD).
This is a legally required test used for the surveillance of TB in cattle throughout the UK.
The BCG (Bacille Calmette-Guérin) vaccine, which is currently used to protect humans against TB and is effective in cattle, is incompatible with the PPD test.
Cattle that are vaccinated with the BCG vaccine, which contains a harmless strain of the bovine TB pathogen Mycobacterium bovis, produce a positive PPD test for TB.
This makes it impossible to distinguish, with the PPD skin test, if the animal has TB or has simply been vaccinated.
Vaccinating cows with BCG is therefore banned in most countries in the world, enabling vets to continue to use the PPD skin test to diagnose the disease in cattle.
Publishing their findings in the journal Scientific Reports, University of Surrey researchers sought to make a new BCG vaccine strain.
The new one lacks some of the proteins that are shared with the pathogen Mycobacterium bovis.
Scientists did this by identifying genes that contain encoded immunogenic proteins that could be removed from BCG without affecting its ability to work as a live vaccine.
The protective efficiency of the new strain was tested in guinea pigs. It was found that TB-infected guinea pigs tested positive for the disease using the synthetic skin test whilst guinea pigs vaccinated with the BCG-minus strain did not.
Unlike PPD, the new skin test also works in animals that are protected from TB by BCG-minus vaccination.
The researchers say this could potentially allow farmers and veterinarians to protect their animals with the new BCG vaccine, whilst still maintaining a diagnostic test that will detect TB.
Johnjoe McFadden, professor of molecular genetics at the university, said: “In order to control the spread of bovine TB, effective vaccination and accurate early diagnosis of the disease are critical.
“This new vaccine provides protection against bovine TB and will help in the fight against this deadly disease which infects over 50 million cattle worldwide and is economically devastating to farmers.”
The next stage of the scientists' work will be to demonstrate that both synthetic skin test and BCG-minus vaccine works in cattle herds.
If they do, then it will be possible to vaccinate cattle against TB yet retain the value of skin test for diagnosis.
