US scientists have discovered that a drug-resistant strain of salmonella carried by pets such as hamsters, mice and rats, could be a significant cause of infection in humans.
The investigation is reported in today’s issue of the New England Journal of Medicine and was led by Dr Stephen J. Swanson from the Epidemic Intelligence Service Program and the Department of Pediatrics at Hennepin County Medical Center, Minneapolis.
The investigators wanted to find out whether a particular antibiotic-resistant strain of Salmonella enterica serotype Typhimurium found in 8 hamsters in 2004 at a pet vendor in Minnesota could be linked to human cases of salmonella infection.
They started by comparing the genetic fingerprints of human-borne salmonella samples with that taken from the hamsters. The genetic fingerprinting method they used was pulsed-field gel electrophoresis (PFGE). The PFGE patterns of the human-borne salmonella were sourced from the National Molecular Subtyping Network for Foodborne Disease Surveillance.
Using PFGE, they found 28 patients had been infected with the same strain of salmonella as that taken from the hamsters.
They managed to track down and interview 22 of the patients and their families. Of these they found that 15 (59 per cent) had come into contact with rodent pets such as hamsters, mice and rats (13 directly and 2 indirectly).
The 15 patients came from 10 different US states and their median age was 16 years – 6 of them had been treated in hospital. They had got their pets from pet stores, breeders and distributors, of which 7 distributors supplying 13 pet stores were found in the 10 states. The researchers were unable to establish whether a single source was responsible for the contaminations.
The same salmonella strain was found in one pet mouse belonging to a contaminated patient and 7 pet store hamsters. The scientists also managed to isolate closely related strains of the bacteria from rodent cages and containers at one of the distributors. All the strains cultured from human, animal and container samples were found to be resistant to a range of antibiotics such as tetracycline, streptomycin, ampicillin, chloramphenicol and sulfisoxazole.
Experts suggest that 1.4 million cases of salmonella infections in humans occur every year in the US. Most of these come from eating contaminated food, but a significant proportion are believed to come from contact with animals, including pets.
Given the results of this investigation the scientists suggest that small pets are probably “an underrecognized source of human salmonella infection”.
Salmonella enterica is a large family of bacteria that includes one that causes typhoid fever. However, when we commonly talk about salmonella, as in this study, we are usually referring to “Salmonella enterica serotype Typhimurium”, the one that causes a form of gastroenteritis with symptoms of stomach pain, fever and diarrhea. These symptoms start some 6 to 72 hours after eating or coming into contact with the germ and last between 3 to 7 days.
Most people recover on their own, perhaps taking some time off work and retiring to bed. But in some people the loss of fluid can leave them very dehydrated and they have to go to hospital to receive intravenous medication to restore their water balance and ease the symptoms. In rarer cases the infection can be fatal if it gets into the bloodstream and is not treated promptly with antibiotics.
Vulnerable people like the elderly, infants and young children, people already sick are more at risk than healthy people. It is particularly worrying that this latest investigation has uncovered a little known source of infection by an agent that is resistant to many of the common drugs used to treat it.
MNT DT
