DoH eyes global warming in rise of local dengue cases
By Margaux Ortiz
Philippine Daily Inquirer
First Posted 18:42:00 04/09/2008
MANILA, Philippines -- The incidence of the dreaded dengue fever is on the rise, and government officials are looking at climate change as one of the major factors behind the phenomenon.
Health Secretary Francisco Duque III announced Wednesday that the number of dengue cases significantly increased for the first two months of this year compared to the same period in 2007.
In a press conference highlighting the role of climate change in the general health of Filipinos, Duque said the DoH noted 6,848 dengue cases from January to March 15 this year compared to the previous record of 5,859 cases.
“This is only a telltale sign that dengue fever is again on the upsurge,” Duque said.
He said that fluctuations in climate variables such as temperature, humidity and precipitation could lead to the proliferation of climate-related diseases such as dengue fever, cholera and typhoid fever.
A study by the DoH's National Epidemiology Center presented during the press briefing showed that there has been a warming trend in the country during the last half century.
Duque said the warming trend peaked in 1998, an El Niño year.
The DoH study further revealed that dengue cases in the country reached a record number of 36,000 in 1998. Some studies pointed to the effect of higher temperatures on the dengue virus by shortening its incubation period.
“The geographic range of Aedes aegypti or the dengue-carrying mosquito is limited by freezing temperatures that kill ... larvae and eggs, limiting the dengue virus transmission to tropical and subtropical regions,” Duque said.
He added that global warming would not only increase the mosquitoes' range but also reduce the size of Aedes aegypti's larvae.
“Since smaller adults must feed more frequently to develop their eggs, warmer temperatures would boost the incidence of double feeding and increase the chance of transmission,” Duque said.
He said the time the virus must spend incubating inside the mosquito would be shortened at higher temperatures.
“For example, the incubation period of the dengue type-2 virus lasts 12 days at 30 degrees centigrade, but only seven days at 32 to 35 degrees centigrade,” Duque said, explaining that shortening the incubation period by five days could mean a potential three-fold higher transmission rate of the disease.
He said studies also showed that the disruption of environmental health services and infrastructure such as water supply and sanitation by climatic events could contribute to a significant rise in water- and food-borne diseases such as typhoid and cholera.
“At present, it is not possible to make accurate health outcomes for the country that might be caused by climate change. Nevertheless, this situation requires us to place climate change in the health development agenda,” Duque said.
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