Authorities are on the alert for possible disease outbreaks after an estimated 2 billion rats chomped their way through crops in 22 counties around Dongting Lake in central China's Hunan Province.

Li Junhua, spokesman for the Hunan Center for Disease Control and Prevention, said Wednesday work teams have been sent to three cities on Dongting Lake -- Yueyang, Yiyang and Changde -- to help prevent outbreaks of disease.

Li said there were no reports of disease caused by rats so far.

The Hunan health department on Wednesday ordered local authorities to initiate a communication campaign.

More than 2.25 million rats -- about 90 tons of rodents -- have been killed since June 21 in Yiyang, local authorities said.

Cao Zhiping, head of the Yiyang office of plant protection and quarantine, said the dead rodents had been buried deep in the earth after being sterilized with quicklime and hence would not cause disease.

In Lujiao town, Yueyang, dead mice were burnt and buried in high ground so that they could not be carried away by flood waters and contaminate the environment.

The estimated 2 billion rats invaded 22 counties around Dongting Lake after their homes on islands in the lake were flooded.

The rats burrowed through dikes and spread out into cropland, devouring crops along their route.

Local authorities in Yiyang, Yuanjiang, Junshan and Huarong are rushing to build walls and dig ditches to keep the rats away from flood-control dikes and cropland.

Poison has also been widely used to kill the mice but has already had side effects. In Binhu Village of Lujiao Town, about one thousand cats died after eating rats killed by poison.

(Xinhua News Agency July 12, 2007)