First analysis of recent disease outbreak in China

Last year, there was major press coverage of an alarmingly large and deadly outbreak of Streptococcus suis disease in Sichuan province in China (see http://www.who.int/csr/don/2005_08_03/en/). Now George Gao, Yu Wang, Jiaqi Tang, Xiaoning Wang and colleagues from the Chinese Academy of Sciences, the Chinese Center for Disease Control and Prevention, and other Chinese institutions publish the first scientific description of the outbreak in the international open-access journal PLoS Medicine.

S. suis is a pathogen with serious economic effects on the pig industry world-wide. The disease is endemic in adult pigs in most countries where pig farming is common. Infections in adult pigs are usually asymptomatic, but infant piglets that get infected through contact with colonized adult females can develop fatal sepsis.

Transmission to humans is rare and generally restricted to individuals with occupational exposure to live or dead pigs. The first human case of S. suis infection was reported in Denmark in 1968. Most of the 200 or so previously reported human cases were characterized by meningitis and septicemia; fewer than 1 in 10 infected humans died.

The recent Sichuan outbreak, in contrast, affected over 200 individuals and killed 38 of them. Besides the large number of infected individuals and the high mortality rate, it was the clinical symptoms associated with this outbreak that attracted interest and worry from scientists and health officials worldwide when the outbreak was first reported.

As Tang and colleagues detail in their article, a large proportion of the infected individuals (including all but one of the patients who died) showed symptoms of Streptococcal toxic shock syndrome (STSS), which had not previously been observed in patients infected with S. suis. However, as Tang and colleagues show, the pathogen in the recent outbreak (as well as in an earlier outbreak in Sichuan province in 1998 that killed 14 of 25 reported patients) was clearly a strain of S. suis. As they describe, both human outbreaks were closely linked to outbreaks in the local pig populations, and there is no reason to believe that any of the cases had been caused by human-to-human transmission.

One of the key questions that arose when the recent outbreak was first reported is whether a new and more virulent strain of S. suis has emerged in China. Tang and colleagues did a genetic study of the S. suis bacteria that they isolated from the Chinese outbreaks to look for unusual characteristics that could explain why these outbreaks were so severe. They did find some differences between the isolates from the two Chinese outbreaks (which appear very similar to each other) and other virulent strains of S. suis. However, more detailed studies are needed before it is clear whether any of these differences are important in explaining why some strains of S. suis are so lethal.

In an accompanying Perspective article, Shiranee Sriskandan and Joshua Slater suggest that S. suis infection "should now be in the list of differential diagnoses when clinicians encounter patients with unexplained sepsis who have a history of exposure to pigs." They conclude that "the emergence of any new zoonotic disease [an animal disease than can be transmitted to humans] associated with high mortality is of global concern" and call for "international collaboration to clarify differences between isolates circulating in different regions of the world."

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Citation: Tang J, Wang C, Feng Y, Yang W, Song H, et al. (2006) Streptococcal toxic shock syndrome caused by Streptococcus suis Serotype 2. PLoS Med 3(5): e151.

PLEASE ADD THE LINK TO THE PUBLISHED ARTICLE IN ONLINE VERSIONS OF YOUR REPORT: http://dx.doi.org/10.1371/journal.pmed.0030151

Related images for press use:

1) http://www.plos.org/press/plme-03-05-gao1.jpg
Caption: S. suis causes a rapidly progressive and fatal sepsis in infant pigs

2) http://www.plos.org/press/plme-03-05-gao2.jpg
Caption: Scanning electron microscopy of S. suis diplococci in a sheet of mucus on the surface of the nasopharyngeal epithelium from a pig. (Photo: Josh D. Slater)

Related Perspective article:

Citation: Sriskandan S, Slater JD (2006) Invasive disease and toxic shock due to zoonotic Streptococcus suis: An emerging infection in the East? PLoS Med 3(5): e187.

PLEASE ADD THE LINK TO THE PUBLISHED ARTICLE IN ONLINE VERSIONS OF YOUR REPORT: http://dx.doi.org/10.1371/journal.pmed.0030187

CONTACTS:

George Gao
Institute of Microbiology
Center for Molecular Immunology
Chinese Academy of Sciences
Zhongguanchun Beiyitiao 13
Beijing, Beijing 100080
China
+86-010-62552530
+86-138-01157380 (mobile)
gaof@im.ac.cn
ggao66@yahoo.com

Shiranee Sriskandan
Imperial College Faculty of Medicine
Hammersmith Hospital
Du Cane Road
London, W12 0NN
United Kingdom
+44 (0)208 383 3135 / 3243
+44 (0)208 383 3394 (fax)
s.sriskandan@imperial.ac.uk

About PLoS Medicine

PLoS Medicine is an open access, freely available international medical journal. It publishes original research that enhances our understanding of human health and disease, together with commentary and analysis of important global health issues. For more information, visit http://www.plosmedicine.org

About the Public Library of Science

The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit http://www.plos.org


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