E. coli O157:H7 in Wild Pigs/California Backgrounder

November 1, 2006 — Liz Wagstrom

With the recent interest in the potential role of swine in the transmission of E. coli O157:H7 to spinach fields in California, Dr. Liz Wagstrom, Assistant Vice President, Science and Technology at the National Pork Board, provided this update on the science concerning E. coli O157:H7 and its implications in swine.

Introduction:

According to the Centers for Disease Control and Prevention (CDC) E. coli O157:H7 is one of hundreds of strains of the bacterium Escherichia coli. Although most strains are harmless, this strain produces a powerful toxin that can cause severe illness in humans. E. coli O157:H7 has been found in the intestines of healthy cattle, deer, goats and sheep. The presence of E. coli O157:H7 in swine feces has been reported in Japan, Norway, Chile and Canada. Recent reports from California indicate that E. coli O157:H7 has been found in the intestinal contents of a wild pig in the area where spinach linked to a nationwide outbreak was grown. Additionally, the same strain of E. coli O157:H7 was found in cattle pastured on land surrounding the spinach field, in other cow manure samples, and in water from a creek located a mile down slope from that field.

Feral Pigs:

Feral, or wild, pigs can be found in many states with California having one of the largest populations. According to the USDA feral pigs are susceptible to several serious diseases and caution should be taken to prevent feral pigs from mixing with domestic swine, as well as if feral swine are harvested for human consumption. Feral pigs are not representative of the U.S. domestic swine herd.

E. coli O157:H7 Surveys in Domestic Swine:

Surveys to determine the prevalence of E. coli O157:H7 in domestic swine were conducted as part of the National Animal Health Monitoring System (NAHMS) 1995 and 2000 studies. In the 1995 study 4,339 swine fecal samples were tested for E. coli O157:H7 from 152 farms in the top swine producing states.

Again, as part of the NAHMS 2000 study 2,526 swine fecal samples were collected from 57 sites in the top 17 swine producing states.

None of the NAHMS 1995 or 2000 samples were found to be positive for E. coli O157:H7.

Discussion of Results/Implications:

The findings in California have demonstrated that E. coli O157:H7 can be isolated from the intestinal contents of a wild pig. However, this finding does not address if the pig was colonized with the bacteria, or if it was a transient infection. A transient infection may occur as the result of animals ingesting feces, feed or water contaminated with the bacteria. The bacteria may then travel through the gastrointestinal tract, but not necessarily colonize and grow in the animal.

Additionally, the finding in a wild pig is not representative of what would be expected in domestic swine grown for pork production. Swine raised in modern confinement production systems are protected from exposure to wild animals and other species of domestic animals.

It is important to note that there is no indication that E. coli O157:H7 in commercial pork products has contributed to human illness in the United States. According to the CDC, E. coli O157:H7 is killed during cooking at an internal temperature of 160 degrees F.

References:
http://www.cdc.gov/ncidod/dbmd/diseaseinfo/escherichiacoli_g.htm#What%20is%20Escherichia%20coli%20O157:H7
Accessed 10/31/2006

http://www.aphis.usda.gov/publications/wildlife_damage/content/printable_version/feral%20pigs.pdf
Accessed on 10/31/2006

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Liz Wagstrom, DVM, AVP Science and Technology, NPB