An intestinal bacterium with a deadly relative

Tuesday, December 8, 2015

In the last of three articles dealing with food-borne zoonotic diseases linked to pigs, veterinary consultant Ernest Sanford discusses Yersinia enterocolitica. Though it only rarely causes food poisoning in humans, a related bacterium devastated 14th century Europe

by ERNEST SANFORD

Yersinia enterocolitica is a bacterium in the group of intestinal bacteria that includes E. coli and Salmonella spp. Of interest, a related Yersinia spp., Yersinia pestis, is the cause of bubonic plague (the Black Death) that ravaged the populations of medieval Europe, and to a lesser extent, Asia and Africa in the 14th century. An estimated 50 million people in Europe died, more than 50 per cent of the population at that time.   

Yersinia enterocolitica is a rare form of food poisoning in humans and is likely unknown to the vast majority of consumers. It results from eating contaminated food, particularly raw or undercooked pork. Clinical symptoms include nausea, abdominal pain and diarrhea, including bloody diarrhea, all characteristic signs of food poisoning. Symptoms usually start four to seven days after initial exposure and may last from one to three weeks, sometimes persisting even longer.

Most cases are self-limiting and are resolved without treatment. Antibiotics, bed rest and consumption of fluids are recommended for more severe cases where clinical symptoms do not cease spontaneously. Illness affects children more frequently than adults, but both children and adults are susceptible.  The elderly and people with a weakened immune system are highly susceptible.

Not all strains of Y. enterocolitica cause food poisoning in humans. The strain that infects humans is found in pigs, but other less pathogenic strains are found in cattle, horses, cats and dogs. Unpasteurized milk, untreated water and contact with infected animals are other sources of human infection with Y. enterocolitica.

Healthy pigs can harbour pathogenic strains of Y. enterocolitica and are a significant reservoir for human infection. The bacterium can be isolated from tonsils, tongue, cheek muscles, lymph nodes, rectal swabs and the intestinal tract of healthy pigs.

Pigs infected by Y. enterocolitica do not become ill and seldom exhibit any clinical signs of the infection, although they harbour the organism and become a source for human infection and food poisoning in those who eat uncooked or undercooked pork contaminated with the bacterium.  As a result, historically, this organism has gone under the radar and there has not been any concerted effort to eliminate it from infected pigs, or to develop methods of identifying infected pigs so they can be treated to eliminate the pathogenic bacterium. It is possible, however, that over time it could become recognized as a significant hazard and efforts would be developed to target and remove the bacterium from infected pigs before they have the opportunity to cause food poisoning. BP

S. Ernest Sanford, DVM, Dip Path, Diplomate ACVP, is a swine veterinary consultant based in London.