Animals 'not the source of drug-resistant salmonella'

Salmonella Typhimurium The researchers examined samples from people and animals infected with a specific type of Salmonella

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Livestock may have been wrongly blamed as being the source of a type of drug-resistant salmonella, a study shows.

UK researchers examined the DNA from 373 humans and animals infected with a specific type of salmonella collected by a Scottish lab over 22 years.

Writing in Science, they say the genetic profiles of the infections in humans and animals were very different.

An epidemic of this strain - Salmonella typhimurium DT104 was seen in animals and humans in the 1990s.

More than 94 million people globally develop food poisoning or gastroenteritis each year after being infected with all types of salmonella.

Drug resistance makes treatments ineffective, causing more complex illness and increased treatment costs.

It had been suggested that such resistance could spread from animals to people via the food chain or through animal waste contaminating the water supply.

'Great surprise'

The team, from the Wellcome Trust Sanger Institute, sequenced DNA from people and animals infected with Salmonella typhimurium DT104.

They looked very different, and the human samples were much more complex than those seen in animals - which would have been the reverse had livestock been the source.

Start Quote

Discovering that the animal and human populations of salmonella were as distinguishable as they were was a great surprise to us”

End Quote Prof Stuart Reid, Royal Veterinary College

Prof Nick Thomson, senior author on the study, said: "Our data provide a very simple message, challenging the established view that local animals are the predominant source of salmonella infections in Scotland.

"This finding will reinvigorate discussions on the sources of antibiotic resistant salmonella infections in humans in other environments."

Prof Stuart Reid from the Royal Veterinary College, who also worked on the study, said: "Discovering that the animal and human populations of salmonella were as distinguishable as they were was a great surprise to us."

And he said the research showed "greater efforts" were needed to identify the major sources of resistance for animals and people.

Writing in the same journal, Dr Mark Woodhouse and Dr Melissa Ward from the University of Edinburgh's Centre for Immunology, Infection and Immunity said: "The results suggest that the human and livestock epidemics were largely independent, though with some jumps in both directions between the two populations."

They suggest the drug-resistant strains could have been introduced via imported food products, but say much more research to pin down the actual source is needed.

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