Farmed carnivores ‘may become disease reservoirs posing human health risk’

Carnivorous animals lack key genes needed to detect and respond to infection by disease-causing pathogens, a new study has found.

Farming large numbers of the meat eating animals, like mink, could allow the formation of undetected disease reservoirs.

In these, pathogens could spread to many animals and mutate to become a risk to human health, researchers suggest.

The research, led by the University of Cambridge, has found that carnivores have a defective immune system, which makes them likely to be asymptomatic carriers of disease-causing pathogens.

Three key genes in the animals that are critical for gut health were found to have lost their function.

If these genes were working, they would produce protein complexes called inflammasomes to activate inflammatory responses and fight off pathogens.

The high protein carnivorous diet is thought to have antimicrobial properties that could compensate for the loss of these immune pathways in carnivores – any gut infection is expelled by the production of diarrhoea, researchers suggest.

But the immune deficiency means other pathogens can reside undetected elsewhere in these animals.

Professor Clare Bryant in the University of Cambridge’s Department of Veterinary Medicine, senior author of the paper, said: “We’ve found that a whole cohort of inflammatory genes is missing in carnivores – we didn’t expect this at all.”

She added: “We think that the lack of these functioning genes contributes to the ability of pathogens to hide undetected in carnivores, to potentially mutate and be transmitted becoming a human health risk.”

Zoonotic pathogens live in animal hosts before jumping to infect humans.

Coronavirus, thought to originate in a wild animal, has shown what damage can be wrought by a novel human disease.

Carnivores – including mink, dogs, and cats – are the biggest carriers of zoonotic pathogens, experts say.

Three genes appear to be in the process of being lost entirely in carnivores – the DNA is still present but it is not expressed, meaning they have become pseudogenes and are not functioning.

Researchers found that a third gene important for gut health has developed a unique mutation, causing two proteins called caspases to be fused together to change their function so they can no longer respond to some pathogens in the animal’s body.

Prof Bryant said: “When you have a large population of farmed carnivorous animals, like mink, they can harbour a pathogen – like Sars-CoV-2 and others – and it can mutate because the immune system of the mink isn’t being activated.

“This could potentially spread into humans.”

Researchers say the results are not a reason to be concerned about Covid-19 being spread by dogs and cats.

There is no evidence that domestic pets carry or transmit Covid-19, and it is when large numbers of carnivores are kept together in close proximity that a large reservoir of the pathogen can build up amongst them, and potentially mutate, researchers say.

The study is published in the journal Cell Reports.