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Chinese scientists have found a new type of contraceptive pills for rats, as some believed the rodents might be linked to the first SARS case this winter on the Chinese mainland.

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

The new contraceptive pill, developed by the Sichuan Provincial Disease Prevention and Control Centre, has won the go-ahead from provincial science and health authorities to begin mass production soon after the Spring Festival, said Yang Shizao, general manager of the Chengdu-based producer Xinjieling Medical Products Company.

The development of the contraceptive pill came as Guangdong Province in South China began a mass culling operation of civets earlier this month and launched a special campaign to exterminate rats and other pests, which some scientists believed could carry the coronavirus causing SARS (severe acute respiratory syndrome).

Scientists suspect that civets may be the source of this winter's first confirmed SARS case on the Chinese mainland, though the World Health Organization (WHO) has said that so far there is no solid proof of this.

"We will kill any rats on sight even if they have no 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 using rat poison to terminate the rodents, saying the traditional rat extermination methods along streets and sidewalks, for fear it 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 the Sichuan Provincial Disease Prevention and Control Centre.

Chinese people used to rely on chemical rodent poisons to rid their homes of vermin, but the problem soon returns since it takes only one or two months for a female mouse to produce a new litter.

To make things even worse, chemical rodent poisons prove to spare no species, even humans themselves, as only 5 milligram of "Dushuqiang," a powerful rat poison, is enough to kill a person.

The contraceptive chemosynthesis baits, with different tastes and fragrances including apples, fish and sesame, all believed to be favoured by mice, will stop the male rodents from producing sperm and do little harm to humans or livestock, said Wang Qiuzhi.

Wang said that these sterilized rats will 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 level since the rodents will keep their mortality rate while their birth rate is much lower," he said.

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

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