Scientists at the University of Surrey in the United Kingdom developed a new vaccine against bovine tuberculosis and a complementary skin test in 2019. Last year they began the first phase of field tests with a larger number of animals, and a few days ago the second phase began.
Currently, the only vaccine available against tuberculosis (TB) is the Bacilo Calmette-Guerin (BCG), which is a live attenuated strain of the bacterium Mycobacterium bovis, the main cause of bovine TB. This is how one described it article of the Animal Health Research Center in Catalonia.
Although the vaccine is capable of conferring partial protection in cattle and studies have been conducted with other vaccines, to date it has not been possible to demonstrate that any of them induces superior protection to BCG. (Lea: This is how bovine tuberculosis is detected in Colombia)
The BCG vaccine, which is currently used to protect humans against TB and is effective in cattle, is incompatible with the tuberculin skin test (PPD)a legally required test used for TB surveillance in cattle around the world.
The current vaccine contains a harmless strain of the bovine TB pathogen. When cattle are tested with PPD, they can test positive, so it is impossible to distinguish whether the animal is infected or has been vaccinated. And when they do test positive, they are usually euthanized.
In 2019 researchers from the University of Surrey in the United Kingdom revealed that created a vaccine that is compatible with synthetic tuberculin which is used in official skin tests to eradicate the disease. They posted their findings in the magazine Scientific Reports.
For this reason, they explain that BCG vaccination is prohibited in most countries of the world, allowing veterinarians to continue to use the PPD skin test to diagnose the disease in cattle. (Read: These are the symptoms of bovine tuberculosis, a long-lasting disease)
During the study, the researchers searched for a way to create a new BCG vaccine that would dispense with some of the proteins it shares with the pathogen. M. bovisidentifying genes that contain encoded immunogenic proteins that can be deleted without affecting the ability of the vaccine to act as a live vaccine.
To make itinjected the cows with a set of BCG strains that each had lost one gene, and survival rates were measured. Thus, the team was able to identify genes that could be deleted without compromising the efficacy of the BCG vaccine.
These genes encoding immunogenic proteins were deleted from the BCG chromosome to construct a ‘BMG-minus’ strain. The deleted proteins were used to develop a new synthetic skin test. the result of which will be negative if the animals were vaccinated with the «BMG-minus» vaccine.
The efficacy of the vaccine was tested in guinea pigs and it was found that those infected with tuberculosis were positive to the standard tuberculin test, while those vaccinated with the BMG-minus vaccine were not.
Unlike the standard skin test, the new test also works in animals protected against TB by the BCG-minus vaccine. This will allow farmers and veterinarians to protect animals with the new vaccine, while maintaining diagnostic tests for the disease.
The new tuberculosis vaccine test
In mid-February, the Irish Journal Farmers newspaper reported that started a second phase of field trials for the vaccine and skin test in England. (Lea: They discover a blood method that improves the diagnosis of bovine tuberculosis)
This next phase will cover at least five commercial cattle farms and 600 animals to evaluate the safety of the CattleBCG vaccine and the safety and performance of the Detection of Infected Among Vaccinated Animals (DIVA) skin test in vaccinated cattle.
It follows the completion of phase one trials in England, where they looked at the safety and performance of the skin test in unvaccinated cattle. The first phase began in 2021 and focused on the safety and performance of the DIVA skin test in unvaccinated animals.
It was done on 10 farms with 524 participating animals, it was completed in May 2022 and the analysis of the results is ongoing. Announcing the news of phase two, England’s Animal and Plant Health Agency (APHA) lead scientist for TB, Dr Phil Hogarth, said that This next step “represents a significant milestone, building on many years of research, and APHA will continue to be led by science, and work tirelessly in the fight to eradicate this disease.”.
For his part, the president of the British Veterinary Association (BVA), Malcolm Morley, described as “very promising” this new stage of trials, which marks an important advance in the ongoing collaborative efforts of the profession. veterinary, scientific community, government and industry to address this disease.
«[El] The BVA identified the development of a vaccine and a test as a research priority that could have [un] significant impact on the eradication of bovine TB in the UK and worldwidealong with other disease control measures. We look forward to seeing the results of these trials,” he noted.
