Streptococcus suis Outbreak, Swine and Human, China
Emerging Disease Notice
August 2005
Summary
An outbreak of Streptococcus
suis in swine and humans in the People’s Republic of
Background
On August 5, 2005 the Director of the Ministry of Agriculture,
People’s Republic of
reported an outbreak of Streptococcus
suis B infection in pigs to the OIE. The
outbreak was first recognized on June 25, 2005 in the prefecture of Ziyang,
Sichuan province, and has reportedly spread to 7 other prefectures in Sichuan. Human cases of S. suis have been reported in all 8 of the prefectures with swine
cases, and in 2 additional prefectures (see map). In 2000, 83.3 million people lived in Sichuan
province, and over 10 million in the capital city of Chengdu. Sichuan
province is the largest producer of pork in
Map source WHO http://www.wpro.who.int/NR/rdonlyres/730601F9-A94B-4B90-A849-A338CA9DCDAC/0/sichuanoutbreakasofaug8.jpg
The number of affected swine premises was not specified in the report to the OIE, although all were backyard farms. As of the report date, there was a total of 6736 susceptible pigs, with 641 cases and 319 deaths (case fatality = 50%). A description of clinical signs in the affected pigs was not provided in the report. Diagnostic testing included isolation, culture, microscopy, fluorescent antibody test, polymerase chain reaction (PCR), and sequencing. Diagnostic tests to rule out avian influenza and Nipah virus were conducted with negative results.
An associated outbreak of S. suis infection in humans was officially reported to the World Health
Organization by
Clinical Presentation and Epidemiology
S. suis is a gram positive bacteria which is endemic in most pig rearing countries of the world. There are 20 serogroups and at least 35 serotypes, with clinical disease in swine usually associated with types 1 and 2. S. suis type 1 occurs mostly in piglets less than 8 weeks of age, causing arthritis (swollen joints) and meningitis (head tilt, paddling, convulsions). S. suis type 2 affects pigs up to market weight, causing an acute disease resulting in meningitis, septicemia, pneumonia, endocarditis and/or myocarditis and death. Additionally, clinical signs may include red skin, enlarged lymph nodes, abortion, genital tract disease, and arthritis. Both types can cause asymptomatic infection and the bacteria may be carried in the tonsils, upper respiratory tract, and vaginal canal for long periods of time. Stress due to poor housing conditions, such as crowding and inadequate ventilation, are risk factors for the development of clinically apparent disease. Transmission occurs through the air and through direct contact with secretions and blood of infected pigs. Piglets can be infected during birth. Environmental contamination may play a role in transmission since the organism can survive long periods in feces, dust, carcasses, and flies.
Human infections with S.
suis can result in meningitis, septicemia, permanent hearing loss (in
50% of cases), pneumonia, endocarditis, and arthritis.
Mortality has been 7% in reported human cases. Toxic shock syndrome may also occur, leading
to multiple organ failure. Transmission
to humans usually occurs when skin wounds, or possibly mucous membranes, are
contaminated by the blood or secretions of infected pigs. Farmers, veterinary workers, and slaughter workers,
therefore, are at increased risk for infection. The incubation period is short, ranging from
a few hours to three days. Cases usually
occur sporadically, with approximately 80 human cases reported in the
Interpretation
The current outbreak of S. suis is atypical for the apparent large number of human cases, high human fatality rate and geographical spread. Epidemiologic and microbiologic investigations of both the swine and human outbreaks are needed to accurately describe the extent of the outbreak and potential risk factors. Conditions that may be contributing to the outbreak include poverty, unsanitary slaughter practices and improper carcass disposal.
For questions or comments about this document, please contact Judy Akkina at (970) 494-7324 or judy.e.akkina@aphis.usda.gov.
References:
OIE Disease Weekly Information Report, August 5, 2005, Vol. 18, No. 31
http://www.oie.int/eng/info/hebdo/a_current.htm#Sec9
World Health Organization (WHO) Disease outbreak news; August 1, August 3, WHO Factsheet on Streptococus suis
http://www.wpro.who.int/media_centre/fact_sheets/fs_20050802.htm
Merck Veterinary Manual http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/53801.htm&word=streptococcus%2csuis
Hong Kong Trade Development Council
http://www.tdctrade.com/mktprof/china/mpsic.htm
Berthelot-Herault, F. Marois C, Gottschalk M, Kobisch M. Genetic Diversity of Stretococcus suis strains isolated from pigs and humans as revealed by pulsed-field gel electrophoresis. J Clin Micro 2002;40(2):615-619.
Streptococcosis. In: Zoonoses and Communicable Diseases Common to Man and Animals, 3rd Ed. Acha PN, Szyfres B, eds. PAHO Scientific and Technical Publication 580; 2001:257-65.
The Epoch Times, news article, August 8, 2005, “Pig Disease Toll Increases to 39” http://www.theepochtimes.com/news/5-8-8/31047.html
The Conservative Voice, news article, August 8 2005, “Second Pig-borne Disease Case Reported in Southern China”
http://www.theconservativevoice.com/ap/article.html?mi=D8BRL6GO2&apc=9020