Risk of animal TB worries scientists

A team of scientists in China say they have produced cloned cattle that have an increased resistance to chronic contagious tuberculosis (TB) in animals.

The disease, known as bovine TB, is caused by a bacteria called Mycobacterium bovis, (M. bovis) which is closely related to the bacteria that cause human and avian tuberculosis. It is contagious in both animals and humans and is a risk to cattle in many countries, including parts of the UK, Africa and Asia.

The research comes against the backdrop of a warning by leading doctors and veterinaries that animal tuberculosis, which is spread through contaminated food, is gradually becoming a greater threat to human health than previously realised.

The disease can be more serious and harder to treat than conventional, human tuberculosis because the bacteria is resistant to the antibiotic pyrazinamide, used to treat human TB.

TB is a bacterial infection spread through inhaling tiny droplets from the coughs or sneezes of an infected person. It mainly affects the lungs, but it can also affect any part of the body, including the abdominal glands, bones and nervous system.

In the cloning process, the Chinese researchers used a more precise genome editing tool to change the genetic code of the cattle in order to improve their resistance to the infectious disease.

DEADLY DISEASE

During the course of their research, 20 calves were born, of which 11 survived for more than three months.

The results from the tests showed that the cloned (transgenic) cattle exhibited increased resistance to the disease compared to the control group.

Tests on resistance to TB were carried out on blood samples taken from the cloned animals. However, it is not clear what would happen if the transgenic cattle were exposed to tuberculosis in normal conditions.

Although the veterinary scientists say this technology could prove very useful in the agriculture sector, Prof Ian McConnell of the University of Cambridge said he doubted whether the research “will have any application to prevention of TB in cattle using transgenic technology.”

And Prof Alan Archibald, head of genetics and genomics at The Roslin Institute, University of Edinburgh, added: “I was not convinced that the authors had demonstrated that the edited calves were resistant — there was no pathology reported for the edited or control animals.”

The same skepticism is shared by Kenyan veterinary scientist Peter Mbatha, who says it may be difficult to have animals that are resistant to the disease as it affects the cells that live within a cell.

“We clone animals to adapt to different environments, but given that animal TB affects the intracellular cells, I do not think it will be easy to stop the bacteria from penetrating the cells,” he explained.

Tuberculosis is one of the world’s deadliest diseases, claiming at least 1.5 million lives worldwide in 2014. The world has committed to being free of tuberculosis by 2035, but international organisations like the World Health Organization say animal tuberculosis — officially known as zoonotic tuberculosis — which has been neglected for decades, is now posing a great threat to human beings.

Animal tuberculosis is spread through contaminated food, primarily raw or unpasteurised milk. The bacterial infection can also affect those, like vets, farmers and butchers, in close contact with infected animals.

Compared to human TB — the biggest lethal infection — which accounted for between 1.1 million and 1.2 million deaths in 2014, the best estimates suggest there are around 121,000 new cases of animal TB each year.