Published Date: 2005-09-11 23:50:00
Subject: PRO/AH/EDR> Streptococcus suis, porcine, human - China (19): OIE
Archive Number: 20050911.2690
STREPTOCOCCUS SUIS, PORCINE, HUMAN - CHINA (19): OIE
A ProMED-mail post
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Journal of Clinical Virology
Date: 10 Sept 2005
Source: Office International des Epizooties (OIE) Disease Information 2005;
18(36), 9 Sep [edited]
_Streptococcus suis_ in China (People's Rep. of ~)
Information received on 5 Sep 2005 (up to 30 Aug 2005) from Mr Jia Youling,
director general, Veterinary Bureau, Ministry of Agriculture, Beijing:
End of previous report period: 5 Aug 2005 (see Disease Information 2005;
18: 245, 5 Aug).
1. General situation
A total of 647 pigs have died as a result of _Streptococcus suis_ infection
in Sichuan province. The deaths occurred in 149 villages of 88
municipalities in 21 counties of the following 8 regions: Chengdu, Deyang,
Luzhou, Mianyang, Nanchong, Neijiang, Zigong, Ziyang.
The epizootic began in late June 2005, reached a peak around 20 Jul, and
then declined sharply. No new cases have occurred since 6 August 2005.
This epizootic was caused by _Streptococcus suis_ type 2. The LD50 (dose
lethal to 50 per cent of the animals) of the bacterial strain isolated in
Sichuan was determined using the new laboratory animal model, zebra fish
(pure breeding line), and the virulence genes of the bacterium were also
The results of the tests showed that the virulence of the isolate is not
significantly different from that of isolates obtained from other places in
the past, and no evidence of genetic variation has been found.
The main characteristics of the epizootic were as follows:
1.1. Spatial distribution
The outbreak areas were mainly centralised in the historical endemic areas
of _S. suis_ infection in Ziyang, Neijiang, and other places. The outbreaks
occurred sporadically, and did not occur densely over a large region.
Infected points were far apart and had no direct epidemiological
relationship. There is therefore little likelihood of transmission having
occurred between them.
1.2. Temporal distribution
The disease was first recognised on 24 Jun 2005, and mainly occurred in
July. During this period the weather was hot, humid and rainy. The season
when the epizootic occurred was the same as in the past. This shows that
the occurrence of _S. suis_ infection in pigs is specific to a particular
1.3. Herd distribution
All outbreaks occurred in remote rural areas with poor economic conditions,
and only in small backyard farms, where animal health conditions are poor,
and pigpens are dimly lit, damp and inadequately ventilated. No outbreaks
were reported in intensive farms and large-scale premises with better
sanitary conditions. The morbidity observed in pigs within each affected
group was low.
2. Control measures
The recent _S. suis_ epizootic was effectively controlled by applying all
of the following measures:
- preventive treatment of pigs in the same herd as infected and dead
animals using highly sensitive antimicrobials, and improvement of
resistance to the disease by adding preventive medicine to animal feed;
- regular disinfection of swine holdings in infected places and zones,
livestock markets and designated slaughterhouses, aimed at improving
- destruction of cadavers of dead pigs by deep burial;
- stepping up of inspection and quarantine, and movement control of animals
and animal products;
- development and production of vaccine, and emergency vaccination of pigs
in high-risk areas aimed at improving their level of immunity.
Pigs have been vaccinated with _Streptococcus suis_ type 2 vaccine.
In the regions of Ziyang, Neijiang and Zigong, where highest morbidity was
found, vaccination was performed in all counties; in the other 5 regions,
vaccination was performed only in the infected counties and in the zones at
risk adjacent to infected zones.
No vaccination was performed in pigs for slaughter within 20 days, one
month old piglets, pregnant sows, or weak pigs. To date, about 14 million
pigs have been vaccinated, and the vaccination cover is up to 90 per cent.
Testing of vaccinated pigs with indirect ELISA showed that 70 per cent of
pigs had a significant serum antibody titre 14 days after vaccination.
The application of vaccine in the field has demonstrated that
_Streptococcus suis_ type 2 inactivated vaccine is effective, safe and has
few side effects.
[While this report indicates all swine cases were confined to 647 cases in
Sichuan province, there appear to have been human cases in Hong Kong. In
fact, the disease is recognized, rarely in pig-producing areas worldwide.
For those looking for details of the distribution and clinical presentation
of _Streptococcus suis_, Steve Berger's posting subtitled "not just China"
provides an excellent, comprehensive summary: Streptococcus suis, porcine,
human - China (16): background 20050819.2436.
Of course, as efficient as electronic information searches can be, they are
still no match for the prodigious memory of Jim Steele when it comes to
past occurrences of zoonotic diseases. Jim, at 92 years of age, still
remembers incidents of disease that everyone else has forgotten. After
reading about the situation in our postings, he contacted me and recalled a
similar event in China in 1970 which involved the spread of _Streptoccocus
suis_ via pork. - Mod.PC]