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 ].