OIE: Streptococcus Suis in China Follow-up report No. 1

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STREPTOCOCCUS SUIS IN CHINA (PEOPLE'S REP. OF ~)

Follow-up report No. 1

 

See also: 5 August 2005

 

Information received on 5 September 2005 from Mr Jia

Youling, Director General, Veterinary Bureau, Ministry

of Agriculture, Beijing:

 

End of previous report period: 5 August 2005 (see

Disease Information, 18 [31], 245, dated 5 August

2005).

 

End of this report period: 30 August 2005.

 

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 July, 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% 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 tested.

 

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 June 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 season.

 

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 sanitary

conditions;

 

- 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.

 

3. Vaccination

 

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 five 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 twenty 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%.

 

Testing of vaccinated pigs with indirect ELISA showed

that 70% 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.