Swine disease in China caused toxic shock syndrome

Apr 12 2006

A large and deadly outbreak of Streptococcus suis disease, in Sichuan province in China last year alarmed health officials worldwide and now scientists from the Chinese Academy of Sciences, the Chinese Center for Disease Control and Prevention, and other Chinese institutions have published the first scientific details of the outbreak.

Streptococcus suis is form of a meningitis which 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 infections.

The dangerous infection that pigs can pass to people appeared in an unusual fatal form last year and according to the Chinese scientists all but one of the people killed by Streptococcus suis in July and August 2005 in China died of streptococcal toxic shock syndrome.

Such a severe type of immune reaction has never been seen in Streptococcus suis infections; transmission to humans is rare and generally restricted to individuals with occupational exposure to live or dead pigs.

The first human case of Streptococcus suis infection was reported in Denmark in 1968, and the majority 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 however affected over 200 individuals and killed 38 of them.

Apart from the large number of infected individuals and the high mortality rate, the clinical symptoms associated with this outbreak were what attracted interest and concern from scientists and health officials worldwide when the outbreak was first reported.

The scientists found the pathogen in the recent outbreak and in an earlier outbreak in Sichuan province in 1998 that killed 14 of 25 reported patients, was clearly a strain of Streptococcus suis.

They believe both human outbreaks were closely linked to outbreaks in the local pig populations, and found no reason to believe that any of the cases had been caused by human-to-human transmission.

The recent outbreak raised the question of whether a new and more virulent strain of Streptococcus suis has emerged in China and the team carried out studies to look for unusual characteristics that could explain why these outbreaks were so severe.

Although they did find some differences between the two Chinese outbreaks and other virulent strains of Streptococcus suis, they say more detailed studies are needed before it is clear whether any of these differences are important in explaining why some strains of Streptococcus suis are so lethal.

Experts advise that anyone who is diagnosed with toxic shock syndrome and who has had contact with pigs should be checked for Streptococcus suis infections.

The researchers, led by George Gao of the Chinese Academy of Sciences in Beijing, said last year's outbreak, which affected 204 people, mostly in Sichuan province, was not unique.

Symptoms of the disease include meningitis and septicemia, a bacterial infection carried in the blood.

Gao says in the fatal human cases, the disease started with acute illness, malaise, fever, headache, diarrhea, rapidly developing high fever, low blood pressure, and a decline of pulse pressure.

A rash was common and the sickest patients fell into a coma with multisystem dysfunction, such as acute respiratory distress syndrome, liver failure, heart failure, internal bleeding, and acute kidney failure.

The findings are published in the journal PLoS Medicine.