19 June 2007

Malaria in Antipolo: Focusing on the Vector

Coupled with the onset of the wet/rainy season from May to December and its topography described as "hilly and mountainous," it is not surprising why Antipolo City in the Philippines is reporting a higher incidence (more than 600 cases!) of malaria cases recently. Malariogenic zones are often described as forested, rural, hilly, mountainous, and remote, according to the DOH advisory on malaria. Whether one is in North Vietnam, in Myanmar, or any other southeast Asian country where malaria is endemic, these environmental conditions seem to be the synonymous requirement of the vector mosquitoes in order to thrive.

In contrast, Dengue vectors prefer urban areas, except in Africa where malaria is present both in urban and rural areas. But hey, that's another story, and I'm digressing.

Why Antipolo? Why "hilly and mountainous" areas?

Because it is cooler there. Yes, the Anopheles mosquito vector prefers to live in cooler areas.

Different parts of the world have different species of Anopheles mosquitoes spreading malaria. See this excellent map to see what I mean. There are 430 Anopheles mosquito species, but only 30-40 species are known to transmit malaria.

In the Philippines, as you probably saw in the map, the principal Anopheles malaria vector is Anopheles flavirostris. It can also be found in Indonesia and in Timor. A recent study last December 2006, suggested that Anopheles flavirostris may have been present in the Philippines since the late Pleistocene period or more than 100,000 years ago. The authors of the study also said there are 3 clades of Anopheles flavirostris species in the Philippines: one basal clade distinct for Mindanao, and two derived clades, one of which was largely confined to Luzon, and one that was widespread.

One study also revealed that Anopheles flavirostris mosquitoes are "shade-loving," and like to breed their larvae on stream-bank shaded areas. I am sure Antipolo has this kind of environment.

Feeding habits? A study done by one of my UP professors in Bataan showed that Anopheles flavirostris mosquitoes feed throughout the night, but are especially active from 10pm to midnight and from midnight to 4am in the early mornings. 'Better sleep under a mosquito net when you live in an endemic area.

Malaria remains to be the 8th leading cause of morbidity in the Philippines, and there are 25 endemic provinces accounting for 90% of all malaria cases. See a previous post for reference. Falciparum malaria accounts for 70% of all malaria cases in the Philippines and P. vivax for the remaining 30%.

The RBM project focuses mainly in Mindanao, and is reportedly making progress there. Eliminating vectors, early consultation, rapid diagnosis and treatment, and newer drugs are all key to controlling the spread of malaria.

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