IT is the longest war in history but human beings will probably never achieve complete victory, because it is waged against pests: rats, mosquitoes, cockroaches, dust mites, termites, flies and others.

Some 5,000 years ago, our ancestors started to burn wood to dispel mosquitoes; however, mosquitoes are still a major public threat, spreading malaria, meningitis and the West Nile virus which has afflicted the United States in recent years.

The direct and indirect economic losses due to diseases spread by rats has reached US$100 billion each year, according to the World Health Organization.

"Under the circumstances of globalization and more frequent travel, human beings are facing more serious pest problems than ever before," said Dr Yoshio Katsuda from Japan, who has been engaged in pest control for over 55 years.

As people travel or move goods around the world by air or ships, pests such as cockroaches are also quickly moved from one location to another.

A type of small cockroach named the German cockroach didn't exist in Shanghai until the 1980s. It first reached the city by ships and aircraft from foreign countries. In the 1990s it began to appear in top-level hotels and in hospitals, reproducing quickly and abundantly.

"Now, our research shows such cockroaches can be found everywhere - in offices, shopping centres and restaurants," said Professor Zhu Longling of East China Normal University.

Migrant birds also bring new viruses when they fly into the country. West Nile virus, carried by birds, may be spread by mosquitoes that plague the birds. The virus later spreads to human beings through mosquitoes bites. "We are worried that this virus which has broken out in North America will affect Asia in the future," said Dr Katsuda.

The "green house" problem has lead to an increase in average temperatures globally, creating a very favourable condition for the spread of pests. The wide use of heating systems has also provided an ideal environment for mosquitoes.

Researchers found that mosquito populations have increased rapidly over the last 20 years in North China because air-conditioning systems are now used in many public places.

In Shanghai, reports say that underground garages have become warm shelters for mosquitoes in winter.

Experts rank rats, cockroaches, mosquitoes and termites as the top pest problems in Shanghai.

Besides investing more in pest control, the critical thing is to change ideas - from elimination to control, experts say.

"Since pests are small in size and quick to reproduce, they can survive the most serious conditions more easily than big animals, including humans. You know, cockroaches have been living on the earth for 350 million years and rats for 50 million years - much longer than human beings," said Zhu.

"So the goal of eliminating pests seems impractical and even stupid. Our previous practice - widely using poisons to kill pests in large areas - has led to many series side-effects."

These results include pollution, poisonous residues in the ground and other living organisms, and drug-resistance among pests.

"We should recognize that pests are part of the ecosystem. Human beings can't kill them all, even by developing more advanced pesticides," said Dr Katsuda.

"What we can do is to control pests to a certain level - so they do not harm our daily life. The most important thing is to care for and improve the environment while controlling pests."