Chinese scientists have found a new type of contraceptive for rats as some believed the rodents might be linked to the first SARS (severe acute respiratory syndrome) case this winter on the Chinese mainland.

"Only one gram of such contraceptive can sterilize 100 rats," said Ma Lin, one of the pill developers in Sichuan Province, southwest China.

The new contraceptive, developed by the Sichuan Provincial Diseases Prevention and Control Center, has won the go-ahead fromprovincial sci-tech and health authorities to begin mass production soon after the Spring Festival season, said Yang Shizao,general manager of the Chengdu-based producer Xinjieling Medical Products Company.

The development of the contraceptive came as Guangdong Provincein south China began earlier this month a mass culling of civet cats and launched a special campaign to exterminate rats and otherpests that some scientists believed could carry virus of the deadly respiratory illness.

Scientists suspect that the civet cat may be the source of thiswinter's first confirmed SARS case on the Chinese mainland though the World Health Organization has said that so far there is no solid proof of this.

"We will kill any rats on sight without mercy even if they haveno direct connection with the SARS epidemic," said Feng Liuxiang, deputy director of the Guangdong Provincial Health Department.

However, some residents in Guangdong urged caution in laying rat poison to terminate the rodents, saying the traditional rat-killing method by placing rat killer along streets and sidewalks would put their children or pets in peril.

"We also prefer contraceptives rather than those virulent rat poisons as the pills will do little harm to human beings and pets," said Professor Wang Qiuzhi with Sichuan Provincial Diseases Prevention and Control Center.

The Chinese used to rely on chemical rodent poison to rid theirhomes of rats and mice, but the problem soon returns since it takes only one or two months for a female mouse to bear a new generation.

To make things even worse, chemical rodent poison proved to spare no species, even humans themselves, as only five milligram of "Dushuqiang," a powerful rat poison, in the human body can cause death.

The contraceptive chemosynthesis baits, with different tastes from fragrance of apple, fishmeal and sesame, all believed to be favored by mice, will stop the male rodents from producing sperm and do little harm to humans or livestock, said Wang Qiuzhi.

Wang said those sterilized rats would still keep their territories within their population and disturb the entire population's reproduction order.

"We can easily keep the rat population at a low density level since the rodents will keep their mortality rate while their birthrate is much lower," he said.

Contraceptives were for the first time used in China earlier inOctober 2003 to contain the population of rats and mice in Shanghai. Those contraceptives used in Shanghai were extracted from plants.

(People's Daily January 27, 2004)