rainfall and DF incidence has been found by previous studies [ 9 , 11 , 13 , 14 ] and also the significant association between temperature and DF incidence [ 10 , 11 , 13 ]. Additionally , humidity ’ s association with DF incidence has been found in one study by Lu L et al [ 10 ]. These three parameters would affect mainly on the number of viable mosquitoes in the environment ready to act as a vector for DF .
With a suitable environment , Aedes Picture 1 Mosquito Life Cycle [ 15 ] mosquito are expected to increase in population starting on day 8-10 after the start of rainy season [ 15 ]. Following the increase in population , the next step for dengue transmission is dengue virus incubation in Aedes mosquito . This step requires 10-12 days for dengue virus to incubate after Aedes mosquito bites infected person . The third step will be the incubation period in human body . The incubation period ( time between exposure and onset of symptoms ) ranges from 4-13 days , some says 4-7 days . The principal symptoms of dengue are high fever ( more than 40 o C ) and accompanied by 2 of the following symptoms : severe headache , severe eye pain , muscle and joint pains , nausea , vomiting , and swollen glands or rash . The symptoms if treated properly last for 2-7 days , after the incubation period after the bite from an infected mosquito . Thus , Carrington and Simmons [ 8 ] proposed that the time gap between the beginning of rainy season and incidence of dengue fever is around 24-30 days [ 8 , 10 , 16 ].
DF , Climate , and Geography of Indonesia
Indonesia is located between the mainland of South East Asian and Australia . Indonesia is made up of 17,508 island with its 5 main islands and covers an area of 1.9 million km 2 . Indonesia is located along the equator , making Indonesia a tropical country [ 17 ].
As a tropical country , climate in Indonesia is fairly even all year round . The main variable of Indonesia ’ s climate is the rainfall , rather than temperature or air pressure . The average annual temperature in Indonesia ranges between 23 o C ( in high mountain areas ) up to 32 o C ( in coastal areas ). Two distinct seasons are monsoon wet and dry season . The rainy season usually start from November to April and the wet season from May to October , but season may vary with a little difference in each location and region [ 17 , 18 ].
Indonesia itself is also affected by the climate change around the world . According to Hulme and Sheard ( 1999 ), mean annual temperature in Indonesia has increased by about 0.3 o C annually , and the overall annual precipitation decreased by 2 to 3 %. However , Boer and Faqih ( 2004 ) stated that there has been a decline in annual rainfall in the south Indonesia , such as in Java , South Sumatera , and South Sulawesi , and an increase in precipitation in the northern region of Indonesia [ 19 ]. Such climate changes are predicted to ease nationwide dengue spread [ 20 ].
In Indonesia , one of the leading risk factor in DF transmission is rainfall index . Regions with high rainfall index tend to have constantly high incidence rate of DF throughout the year . Conversely , regions with low rainfall index tend to have high DF incidence rate only after the rainy season starts to begin [ 7 ].