Higher temperatures and heavier than normal rainfall levels have contributed to the sharp upturn in the rate of infection, said Kevin Palmer, regional adviser in vector-borne and parasitic diseases at the WHO Western Pacific office here.

The UN agency said 189 people had died from the mosquito-born disease in the areas covered by the office - the Pacific, Australasia, East Asia and parts of South East Asia. A total of 46,456 cases had been registered in the region in 2001, the highest incidence of the mosquito-born disease since 1998, when more than 356,000 people were infected.

In the whole of last year there were 167 deaths from 45,603 reported cases across the Asia-Pacific region.

The WHO figures do not include 44 deaths reported by Vietnamese authorities or a further 107 registered in Thailand.

Outside Thailand, the hardest hit countries have been Cambodia, which has reported 90 deaths from 4,163 cases so far this year followed by the Philippines with 67 from 7,697 cases.

"Levels seen so far in 2001 have been below those seen in 1998 but are higher than in 1999 and 2000, which gives rise for concern," the WHO said in a statement.

Palmer said "a combination of changes in the weather lead to more mosquito vectors".

He cited a slight increase in temperatures this year as well as heavier rainfall that coincides with the El Nino weather phenomenon.

Palmer said dengue outbreaks in the region followed a three-year cycle of infection and subsequent development of immunity to one of four strains.

"The population becomes immune after a while before another strain comes again," he told AFP.

The second and third type is now infecting Southeast Asia while the type one virus has hit the Pacific, he added. A type three strain caused the 1998 epidemic, Palmer said.

The UN agency urged all tropical countries in the region to step up surveillance to detect potential outbreak areas quickly, and to implement epidemic control measures.

"Vector control measures aimed at eliminating mosquito breeding sites should begin in outbreak-prone areas early. They offer the best means of both preventing outbreaks and reducing the severity of outbreaks when they do occur," it added.

"The message given to the public has to be clear: even small water collections in their gardens or even inside their houses can result in sickness or death due to dengue."

Dengue fever is an acute infectious disease caused by a virus borne by Aedes aegypti mosquitoes that breed in water.

Normal symptoms include fever, headache, severe joint pain, and rashes.

A more virulent strain of the disease can cause sharp falls in blood pressure and internal bleeding leading to death in five per cent of cases.

The highest number of cases this year has been in French Polynesia, where an estimated 28,600 people were infected in an outbreak which started in January.

The epidemic there killed four people but now appears to be under control, WHO said. Non-fatal cases have also been reported in Samoa and New Caledonia.

Other affected countries include Malaysia, which has registered 26 deaths from 4,464 cases and Singapore, where there have been two fatalities out of 1,334 cases this year, according to the WHO.

The governor of Bangladesh's central bank was flown to Bangkok last week for treatment after coming down with the disease.

Dengue fever has also caused concern in Latin America with Venezuela hit by an epidemic in which nearly 25,000 people have been infected with a strain of the disease not previously seen in the country.