All three are transmitted to humans by mosquito bites. Malaria and dengue fever are prevalent in East Timor where rice fields, streams and pools provide breeding grounds for the different mosquito species which carry them. Japanese encephalitis has not yet been detected in East Timor, but it also poses a significant risk, as the mosquitoes, which transmit it, are common in the country. The onset of the island's rainy season, lasting from November to March, accelerates mosquito breeding. Since the conflict in East Timor, unusually high number of mosquitoes have been breeding in the pools of water which have collected amongst the debris, leading to large outbreaks of dengue fever, especially in the capital, Dili.
Malaria is thought to be the most common insect borne disease in East Timor.
Like dengue fever and Japanese encephalitis, it involves recurring fever and can kill in its severest form. Pregnant women and young children are the most vulnerable. However, past experience in post-conflict situations has shown that all people's immunity to disease is weakened when they are homeless or living in crowded shelters, with inadequate food supply and poor access to water and sanitation facilities. The most powerful weapon in the fight against insect-borne disease in East Timor is therefore its prevention, although good diagnosis and treatment must follow when disease is present. East Timor has not had an effective mosquito control programme for decades.