Scientists have developed a novel vaccine and complimentary skin test to protect cattle against and spread of bovine tuberculosis (bovine TB).
Researchers reveal they have for the first time created a vaccine that is compatible with a synthetic form of the tuberculin skin test (PPD), a required test used for the surveillance of TB in cattle throughout the UK.
Bovine TB is an infectious disease in cattle affecting their lungs, and those that test positive for the disease culled.
The BCG vaccine, which is currently used to protect humans against TB and is effective in cattle, is incompatible with the PPD test.
Vaccinating cows with BCG is so banned in most countries in the world, enabling vets to continue to use the PPD skin test to diagnose the disease in cattle.
By identifying genes that contain encoded immunogenic proteins that could be removed from BCG without affecting its ability to work as a live vaccine.
To do this, a collection of BCG strains that had each lost a single gene injected into cows and survival rates measured.
This allowed the team to identify genes that could be removed without compromising the BCG vaccine’s effectiveness.
These dispensable genes encoding immunogenic proteins were then deleted from the BCG chromosome to make a BCG-minus strain.
The deleted immunogenic proteins were then used to develop a new synthetic skin test that, like PPD, will be positive for animals that have exposed to TB but, unlike PPD, will be negative for animals that have vaccinated with the BCG-minus strain.
The protective efficiency of the new strain tested in guinea pigs. It 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.
So, unlike PPD, the new skin test also works in animals that protected from TB by BCG-minus vaccination.
This allows farmers and veterinarians to protect their animals with the new BCG vaccine, whilst still maintaining a diagnostic test that will detect TB.
To control the spread of bovine TB, effective vaccination and accurate early diagnosis of the disease are critical.
This new vaccine protects bovine TB and will help in the fight against this deadly disease which infects over 50 million cattle worldwide and is devastating to farmers.
The next stage of our work will be to show that both synthetic skin tests and BCG-minus vaccine work in cattle herds. If they do, then it will be possible to vaccinate cattle against TB yet keep the value of skin test for diagnosis.