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Chapter 195 Yersinia

The genus Yersinia is a member of the family Enterobacteriaceae and comprises >14 named species, 3 of which are established as human pathogens. Yersinia enterocolitica is by far the most common Yersinia species causing human disease and produces fever, abdominal pain that can mimic appendicitis, and diarrhea. Yersinia pseudotuberculosis is most often associated with mesenteric lymphadenitis. Yersinia pestis is the agent of plague and most commonly causes an acute febrile lymphadenitis (bubonic plague) and less commonly occurs as septicemic, pneumonic, or meningeal plague. Untreated and delayed treated plague has significant mortality. Other Yersinia organisms are uncommon causes of infections of humans, and their identification is often an indicator of immunodeficiency. Yersinia is enzootic and can colonize pets. Infection of humans most often results from contact with infected animals or their tissues; ingestion of contaminated water, milk, or meat; or, for Y. pestis, the bite of infected fleas. Association with human disease is less clear for Y. frederiksenii, Y. intermedia, Y. kristensenii, Y. aldovae, Y. bercovieri, Y. mollaretii, Y. rohdei, and Y. ruckeri. Some Yersinia isolates replicate at low temperatures (1-4°C) or survive at high temperatures (50-60°C). Thus, common food preparation and storage and common pasteurization methods might not limit the number of bacteria. Most are sensitive to oxidizing agents.

195.1 Yersinia enterocolitica


This agent is transmitted to humans through food, water, animal contact, and contaminated blood products. Transmission can occur from mother to newborn. Y. enterocolitica appears to have a global distribution but is seldom a cause of tropical diarrhea. There is approximately 1 culture- confirmed Y. enterocolitica infection per 100,000 population/yr in the USA, and infection may be more common in Northern Europe. Cases are more common in colder months and among younger persons and boys. Most infections in children are among those <7 yr of age, with the majority among children <1 yr of age.

Natural reservoirs of Y. enterocolitica include pigs, rodents, rabbits, sheep, cattle, horses, dogs, and cats, with pigs being the major animal reservoir. Contact with feral animals or a colonized pet is a common source of human infections. Culture and molecular techniques have found the organism in a variety of foods, including vegetable juice, pasteurized milk, and carrots and in water. A source of sporadic Y. enterocolitica infections is pig offal (chitterlings). In one study, 71% of human isolates were indistinguishable from the strains isolated from pigs. Y. enterocolitica is an occupational threat to butchers. In part because of its capacity to multiply at refrigerator temperatures, Y. enterocolitica is transmitted at times by intravenous injection of contaminated fluids, including blood products.

Y. enterocolitica infections have increased, and Y. pseudotuberculosis infections have declined, leading to the suggestion that the former organism is replacing the latter in an ecologic niche. In part, the mass production of animals, development of meat factories based on chains of cold storage, and international trade of meat products and animals are believed to be the reasons for the increasing prevalence of yersiniosis in humans. There is evidence that under farm conditions pigs can be raised free of Y. enterocolitica.


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