Wild game ousts pork as main source of Trichinella infection

Jul 25, 2003 (CIDRAP News) –Wild game meat, especially bear meat, has replaced pork as the leading source of Trichinella infections in humans, according to the Centers for Disease Control and Prevention (CDC).

Of 72 trichinellosis cases reported from 1997 through 2001, 31 were linked to eating wild game, while 21 cases resulted from eating pork from domesticated swine. The source of the parasitic infection was unknown in the other 20 cases, the CDC reports today in a supplement to Morbidity and Mortality Weekly Report.

The CDC's latest figures also show continuation of the long-term decline in human trichinellosis, from a median of 393 cases a year between 1947 and 1951, with 57 deaths, to a median of 12 cases a year between 1997 and 2001, with no deaths. (The report cautions that the actual number of cases is probably higher, because surveillance is not designed to pick up asymptomatic cases.) The decline is largely the product of stricter standards and regulations in the pork industry, the article says.

"Because of the successful reduction in Trichinella prevalence among swine in the U.S. commercial pork industry, the majority of cases of human trichinellosis are now associated with wild game meat, noncommercial pork, and foreign pork," the CDC says.

Trichinellosis is caused by eating uncooked or poorly cooked meat infected with the roundworm Trichinella spiralis. The infection can cause initial gastrointestinal symptoms and low-grade fever, which may later give way to various other symptoms as the roundworm larvae move to the muscles and form cysts there, according to the report. In the 72 cases reported, the most common symptoms were myalgia and fever, occurring in 46 and 33 patients, respectively. Seventeen patients had no symptoms.

Of the 31 cases linked to wild game, 29 were associated with bear meat, 1 with cougar meat, and 1 with wild boar, the report says. The cases traced to non-wild pork products included 12 involving commercially produced pork and 9 involving home-raised or "direct-from-farm" swine. The commercial pork cases included 8 linked to U.S. pork and 4 involving foreign pork (eaten in Egypt, Vietnam, and Yugoslavia). Of the 20 cases in which the source of infection was unknown, 5 had possible links to both pork and nonpork products. In 20 of the 72 cases, the person ate uncooked meat.

The CDC says the steady decline in trichinellosis is in part a result of regulatory changes that have reduced the exposure of domestic swine to Trichinella. The estimated prevalence of the parasite in swine dropped from 1.41% in 1900 to 0.125% in the late 1960s and to 0.013% in 1995. Changes in commercial pork processing methods and increased public awareness of safe cooking and freezing methods have also contributed to the decline in cases, the report says.

While trichinellosis cases related to eating pork have decreased, the number of reported cases related to eating nonpork products has stayed constant since 1982, according to the CDC. The 1997-to-2001 period marked the first time cases linked to nonpork products surpassed those traced to pork.

The US Department of Agriculture recommends cooking fresh pork to an internal temperature of 160ºF to ensure killing of Trichinella and other pathogens, the article notes. Long-term freezing (6 days at -20ºF for meat less than 6 inches thick) also can kill T spiralis in pork.

CDC. Trichinellosis surveillance—United States, 1997-2001. MMWR Surveillance Summary;52:SS-6 [Full text]

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