Pig Disease in China Worries UN More Testing is Requested on Deadly Outbreak in Humans
The World Health Organization has urged China to conduct more tests to clarify perplexing aspects of the largest outbreak in humans of a bacterial pig disease, including why the death rate among patients has been unusually high.
China has reported that the disease, caused by Streptococcus suis bacteria, infected 206 people in Sichuan Province from June 24 through July 21. Of these, 38 or nearly 1 in 5 died, and 18 are critically ill.
Most cases have occurred among adult male farmers who have had close contact with diseased pigs or have eaten uncooked pig products.
The bacteria are commonly found where pigs are raised. Animals without symptoms carry the bacteria in their tonsils and noses. Sichuan Province has one of the largest pig populations in China, and news organizations have reported a concurrent outbreak among pigs in that area. There is no evidence that the illness has been transmitted from one person to another in the outbreak, the health agency said.
Many patients have developed meningitis, an inflammation of the covering of the brain and spinal cord, with symptoms that can include a high fever, malaise, nausea and vomiting. In the past, about half of the patients who recovered from meningitis caused by Streptococcus suis became deaf.
The interval between exposure to Streptococcus suis and the onset of illness ranges from four hours to three days. The infection can progress rapidly.
Chinese officials say they are searching for cases and that the outbreak is under control. But Dick Thompson, a World Health Organization spokesman, said Thursday, “We do not have enough information to determine that.”
China, he said, is promptly reporting new developments to the World Health Organization and the Food and Agricultural Organization, each a United Nations agency.
There was no immediate evidence that China, which came under fire for covering up the outbreak of SARS, or sudden acute respiratory syndrome, in 2002 and 2003, was hiding information about the Streptococcus suis outbreak.
“We believe the Chinese are being transparent, but we have asked for more information,” particularly because of the unusual features of the outbreak, Thompson said.
Streptococcus suis infections usually occur sporadically or in small outbreaks, said Jorgen Schlundt, a Danish veterinarian who directs the department of zoonoses and food-borne diseases at the health agency. (Zoonoses are infectious diseases that occur primarily in animals but that can be transmitted to people.) Scientists say that the bacteria can survive for long periods in feces, dust and carcasses, but can be easily killed by common disinfectants.
Health officials say more laboratory tests are needed to determine why the Sichuan outbreak is so large and the death rate so high. Among the questions infectious disease specialists have raised is whether Streptococcus suis has mutated to become more virulent. Scientists say China should search for other factors that might explain the high death rate. Another unusual feature of the outbreak is that many patients have developed bleeding under the skin, and some have developed toxic shock syndrome.
The infection has been detected by growing the bacteria on a culture in a laboratory, which can take more than a day. To detect cases more quickly, Chinese scientists have adapted a technique known as polymerase chain reaction.
Chinese scientists are also producing large amounts of a vaccine to prevent the spread of the bacteria among pigs, but the effectiveness of such immunization has not been proved, the WHO said.