Unexplained deaths of farmers await diagnosis.
Over the past month, an unknown disease has killed at least 17 people and infected 41 others in southwest China, the Xinhua news agency reported on 24 July.
No one has yet been able to identify the cause of the illness, which has flu-like symptoms and seems to be spreading to farmers from livestock in towns near the cities of Ziyang and Neijiang in the Sichuan province.
"We don't have a diagnosis. We have an ongoing investigation by the Chinese, and we will wait for them to make the diagnosis on the spot," says Bob Dietz, a spokesman for the World Health Organization (WHO) Western Pacific Regional Office in Manila, the Philippines.
"It could be any one of an entire range of diseases including avian flu or SARS (severe acute respiratory syndrome), but frankly the greater concern is that we don't know what it is."
“It could be any one of an entire range of diseases including avian flu or SARS, but frankly the greater concern is that we don't know what it is. Bob Dietz , World Health Organization's Western Pacific Regional Office in Manila”
Such sudden, unexplained deaths linked to animals are rare, and China has sent an emergency team to the area to investigate whether they are linked to avian flu. It is encouraging that the outbreak was picked up and announced relatively quickly, despite the fact that the cases have occurred in very scattered regions, says Dietz.
Detecting the problem within four weeks is "not bad" he says, adding that detecting a similar event even within a city such as New York might take up to two weeks. "China announced it and told us and the media; its surveillance system is working."
Officials within China claim to have crossed some major diseases off the list of culprits. "I can assure you that the disease is absolutely not SARS, anthrax or bird flu," Zeng Huajin, a senior official with the local health department, told Xinhua news.
Huajin says the probable cause is the bacteria Streptococcus suis. This is a major pig pathogen, and routinely found in most countries of the world. Human infections are rare, with less than 150 cases reported in the world literature according to the UK Health Protection Agency.
Patients with S. suis infections have severe flu-like symptoms and may also experience deafness. Xinhua describes the symptoms of the unidentified outbreak as "high fever, fatigue, nausea and vomiting, and becoming comatose later with bruises under the skin". Those affected, it said, were farmers who had butchered diseased pigs or sheep.
Scientists and doctors are sharing thoughts on the ProMED mailing list, a service for disseminating information about outbreaks. They suggest that the symptoms are similar to Crimean-Congo hemorrhagic fever (CCHF), which is endemic among livestock in parts of southern China.
CCHF is a rare but severe disease, usually spread by ticks, with a high mortality rate. It would pose a limited risk to people as it does not spread from human to human.
Eye on the birds
As the hunt for a diagnosis continues, scientists are still warning of the dangers of bird flu.
Thousands of migratory birds at Qinghai Lake in western China became infected with H5N1 avian flu virus this spring, and scientists have warned that they could spread the disease widely. Scientists from the WHO have confirmed that this virus is a new form of highly virulent H5N11.
Pigs can carry both avian and human flu strains, and so could serve as a vessel in which the two swap genes, generating a contagious human virus. Hualan Chen, director of the National Avian Influenza Reference Laboratory in Harbin, Heilongjiang province, says that, as of April, 23% of 450 Chinese pigs tested were carrying a less virulent avian flu strain: H9N2.
WHO officials are still waiting for China to clear visits to other areas where there have been bird flu outbreaks. They say that the country is not meeting requests for further information and virus samples. Julie Hall, a coordinator at the WHO's Beijing office, says getting this material is a "matter of urgency".
ChenH., et al. Nature, 436. 191 - 192 (2005).
World Health Organization's Western Pacific Regional Office in Manila