Outbreak of swine disease in China takes human toll

Published on September 15, 2005
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The World Health Organization continues to monitor an outbreak of Streptococcus suis in pigs in China that has infected more than 200 people.

As of late August, the Ministry of Health of China had reported 215 cases of human disease associated with the outbreak. Of these human cases, 39 have been fatal. No new cases had been reported since Aug. 5, according to the WHO.

Data provided by China depict an outbreak that peaked from the second through the fourth week of July, and dwindled rapidly thereafter. Authorities say several human cases were discovered retrospectively once the epidemiologic investigation was under way.

Streptococcus suis is a species of bacterium found in many parts of the world where pigs are raised. It is most adapted to domesticated pigs, but is also occasionally found in wild boars, horses, dogs, cats, and birds.

Infected pigs usually are without clinical signs, but the infection can result in septicemia, meningitis, pneumonia, and arthritis.

The most important risk factor in acquiring the infection is contact with pigs or uncooked pork products. Typically farmers, veterinary personnel, abattoir workers, and butchers are the risk groups. Transmission to humans is most likely through wounds on the skin, including minor abrasions. The incubation period ranges from a few hours up to three days.

The initial human victims during this latest outbreak were suspected of having hemorrhagic fever with renal syndrome, but laboratory tests ruled that out. More cases were then reported, with a range of symptoms: high fever, malaise, nausea and vomiting, followed by meningitis, subcutaneous hemorrhage, toxic shock, and in severely affected people, coma.

Nearly all of the patients were reported to be local farmers and butchers by profession who had been killing sick pigs or processing and selling the meat. More than 40 percent of the patients were aged between 50 and 60 years.

Subsequently, results of laboratory tests on several of the human samples confirmed infection with S suis serotype 2. A concurrent investigation by the Ministry of Agriculture of China discovered the presence of S suis serotype 2 in pigs in the area.

Chinese authorities say tests on human samples have not shown the presence of any other bacterial agent. A viral cause was also considered in pigs, and both influenza and Nipah virus infections were reported to have been ruled out.

Authorities add that, on the basis their investigation so far, there is no evidence of human-to-human transmission, and no health care workers tending to the patients have been infected. The Ministry of Health says further study is still needed, however, to try to determine why this outbreak was so large, including so many fatalities, especially compared with outbreaks in recent years.