China tackles plague carrying gerbil explosion

Chinese authorities are feeding contraceptive-laced bait to a wild rodent species that is a known carrier of the bubonic plague, Xinhua reported last week.

The massive population explosion of wild gerbils in the northwestern province of Xinjiang is causing havoc with the environment as well as agriculture, worsening the effect of desertification.

Great gerbils are also carriers of the yersinia pestis bacteria, the cause of bubonic plague, and are common in several central Asian countries

Authorities have been placing bran-like pellets containing a drug that causes infertility near the entrances of the mammals’ extensive burrows in the Gurbantunggut desert since last May.

“Besides pregnancy prevention, the drug can induce abortion, and thus largely reduce their breeding rate,” said Du Yuefei, head of the Changji city epidemic prevention.

“It’s a good way to tackle the desert plague,” he told Xinhua.

The drug, which has been spread across 49,000 hectares (121,000 acres), has “little effect” on other animals, according to the report.

Gerbils horde massive amounts of grass in their complex burrows and cause damage to root systems, according to Xinhua.

A 2004 study in neighbouring Kazakhstan of the same species of gerbil, whose latin name is rhombomys opimus, found that bubonic plague outbreaks could be predicted by the rise and fall of wild populations.

"We found a fairly simple pattern - if the population of gerbils increases in density, when they reach a certain level, two years after that plague appears," Herwig Leirs of the University of Antwerp was quoted as saying in New Scientist magazine.

Leirs drew on data that had been meticulously collected by soviet scientists during the cold war era. Western powers had feared that the USSR would use the information for biological warfare, New Scientist reported.

Gerbils are effective carriers because they can transmit the plague without being affected by it.

"If a population is dense enough then the disease can persist because there is frequent contact between infected and susceptible individuals," Leirs told New Scientist.

The bubonic plague is endemic in several countries and China reported 519 cases to the World Health Organization between the years of 1989 and 2003, with 52 of them fatal.

The gerbil explosion in Xinjiang was last reported in 2003, when the Chinese government introduced a scheme using
predatory birds to control the desert rodents.

Changji City installed 300 perches for owls and eagles, Meng Jijin, an official in desert administration told Xinhua.

It was the worst rodent disaster in Xinjiang in 10 years, according to Xiong Ling, a local pest control official.

Massive networks of burrows had destroyed more than four million hectares (11 million acres) of praries, the BBC reported

The latest report in the Chinese state media makes no mention of the previous campaign and it is not clear how successful the predatory birds were.

In the meantime sterilizing the rodents could damage ecosystems, experts told the Guardian newspaper.

"That the pellets have 'little effect' is highly debatable," a conservationist told the British newspaper anonymously.

"All drugs have an effect when put into the system, on other rodents, on birds of prey that eat the rodents and so forth."

They also warn that that culling gerbils could harm other animals in the food chain including bears, eagles and leopards.

A similar but unrelated grassland mammal, the Pika, has been subject to poisoning by the Chinese government since 1958, the China Daily reported in 2004.

The round-eared, whiskered mammals cause the same kind of rampant damage to plateau grasslands as the gerbils.

But the campaign to poison them has been challenged by ecologists who say the species helps to maintain biodiversity.

"When you see the black-eared kites, the area probably has not been poisoned. Contrarily, if there is nothing in the sky, you can tell the pikas are not there any more," US biologist Andrew Smith told students at Peking University in 2004.