'Farming mink, dogs, and cats may spur disease reservoirs'

Carnivorous animals have a defective immune system, which makes them likely to be asymptomatic carriers of disease-causing pathogens, finds a study.

Thus, farming large numbers of carnivores, like mink, dogs, and cats -- who are the biggest carriers of zoonotic pathogens -- could allow the formation of undetected "disease reservoirs", in which a pathogen could spread to many animals and mutate to become a risk to human health, said researchers from the University of Cambridge.

They discovered that carnivorous animals lack three key genes needed to detect and respond to infection by pathogens: the DNA is still present but it is not expressed, meaning they have become 'pseudogenes' and are not functioning.

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.

If these genes were working, they would produce protein complexes called inflammasomes to activate inflammatory responses and fight off pathogens, said the findings, published in the journal Cell Reports.

The researchers say that the carnivorous diet, which is high in protein, 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. But the immune deficiency means that other pathogens can reside undetected elsewhere in these animals.

"We've found that a whole cohort of inflammatory genes is missing in carnivores -- we didn't expect this at all," said Clare Bryant, Professor at the University of Cambridge's Department of Veterinary Medicine.

"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," she added.

However, the results are not a reason to be concerned about Covid-19 being spread by dogs and cats, researchers said.

There is no evidence that these domestic pets carry or transmit Covid-19. It is only 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, they noted.