Mosquitoes with dengue virus 'doubly dangerous'

The Department of Medical Sciences’ National Institute of Health yesterday revealed that one mosquito can carry two strains of dengue fever, as larvae can be infected with viruses through their mothers.

The NIH also warned that this year’s weather changes could lead to an outbreak of the disease.

After receiving an award for outstanding research yesterday for her study of the biology and infection rate of mosquitoes carrying dengue fever, NIH researcher Usavadee Thavara said she conducted the study in 25 dengue-hit provinces from 2006 to 2010 and found that two species of mosquitoes, Aedes aegypti and A albopictus, spread the disease’s four strains.

The two species also evolved from usually living at altitudes no higher than 500 metres above sea level to being found at places as high as 1,509 metres at Chiang Rai’s Doi Tung area and 1,928 metres at Chiang Mai’s Doi Angkhang area. The two species, formerly active only in daytime, now also hunted at night, she said.

While A aegypti’s highest biting rate was 45 mosquitoes per person per hour during summer, A albopictus’ highest rate was 18 per person per hour in winter, she said.

The research also found that some mosquitoes could carry two dengue strains, as the mothers could pass on the virus to eggs so that when the larvae became adults they were ready to spread the virus, without needing to acquire it from a host. Previously it was believed that mosquitoes had to bite an infected person first to get the virus, she said. Hence the eradication of larvae would prevent a dengue outbreak.

Another NIH scientist, Apiwat Thawatsin, reported that in 2008, 89,626 people in Thailand contracted the disease, resulting in 102 deaths, while 2009 saw 56,651 patients and 50 deaths, and last year there were 113,017 patients and 139 deaths.

For this year, he said there would be a serious dengue fever outbreak due to weather changes such as heavy rain in summer. People should prevent outbreaks by destroying mosquito incubation grounds, such as by putting Abate sand into standing water, he urged. Abate is a trade name for the larvicide temefos.

-The Nation/Asia News Network