A batch of raw pet food produced by the British company Natural Instinct has been identified as the probable cause of a rare outbreak of feline tuberculosis that infected 13 cats last year in the United Kingdom.

The Camberly-based company confirmed to the VIN News Service today that it is working with Britain's Food Standards Agency as part of a related investigation into its now-discontinued "Wild Venison" product.

Natural Instinct ships only within the U.K. and Ireland, although it is able to deliver products outside the country "on occasions," according to the company's website.

Its Wild Venison line, containing deer meat, was singled out following a separate probe into the TB cases by a group of veterinarians and academics. The results of their study were published this week in the Journal of Feline Medicine and Surgery.

The study found "compelling, if circumstantial, evidence" of an association between the infected animals and a commercially-available raw food product made by a single manufacturer. The study does not name the company, but Natural Instinct confirmed its involvement.

Cats in five of six clinical cases were either too sick to treat or deteriorated despite therapy, giving a mortality rate of 83%, the researchers found. Another seven cats showed evidence of infection but did not require clinical attention.

Not long after reports of the outbreak surfaced in November — and before investigations into its causes were concluded — Natural Instinct recalled its Wild Venison product. The recall occurred "because some of the ingredients were not inspected in line with European Union requirements," according to a food alert published Dec. 11 by the Food Standards Agency.

A spokesperson from Natural Instinct said by email: "Everything we do at Natural Instinct is done so with the best interests of our customers and their pets in mind. We can assure our customers that Natural Instinct followed, and continues to follow, every food standard, hygiene regulation and best practice required to produce raw pet food in the commercial marketplace."

The UK Animal and Plant Health Authority regularly conducted inspections on the company and was satisfied that all standards were met, the spokeswoman said.

"Even though we no longer manufacture and sell the venison cat product, we are continuing to work with Food Standards Agency as part of the investigation into the product," she added.

Raw pet food is more apt to be contaminated with pathogens than dry pet food, judging from the results of a study published in 2014 by U.S. Food and Drug Administration researchers and collaborators. In the study, of 480 dry and semi-moist pet food samples, two tested positive for Listeria, Salmonella and toxigenic forms of Escherichia coli. By contrast, of 576 samples of raw dog and cat foods, exotic animal feed and jerky-type treats, 66 tested positive for the same pathogens (with all of them isolated to raw foods and jerky-type treats).

Suspicions that raw cat food was responsible for the UK tuberculosis outbreak were high early on, given that the infected animals lived exclusively indoors and couldn't hunt outside.

The pets caught a strain of TB caused by Mycobacterium bovis, a bacterium more typically found in cattle and wild animals such as bison, elk and deer. Infection typically is cutaneous and caused by bite wounds and contamination from infected rodents.

The pathogen can affect humans; however, by far the more common cause of TB in people is Mycobacterium tuberculosis.