Dengue outbreak is closely associated with temperature and rainfall. Hence, researchers in India have developed models based on different climatic zones of the country. It has been found that a rise in temperature from 17 to 30 degrees celsius may increase transmission of dengue fourfold, however, increase in mercury beyond 35 degree celsius is not suitable for survival of mosquito.
The study was conducted by the University of Liverpool Britain in collaboration with the Hyderabad-based Indian Institute of Chemical Technology (IICT) and National Institute of Pharmaceutical Education and Research (NIPER), Guwahati. The researchers evaluated the relationship of climatic factors in the spread of dengue in different climatic zones in the country through the states of Punjab, Haryana, Rajasthan, Gujarat and Kerala.
They focused on changes in a factor called "extrinsic incubation period (EIP)" of the dengue virus by taking into account daily and monthly mean temperatures in these areas. EIP is the time taken for incubation of the virus in the mosquito. During this period, after the mosquito draws a virus-rich-blood meal, the virus escapes the gut, passes through the mosquito's body and reaches its salivary glands. Once this happens, the mosquito is infectious and capable of transmitting the virus to a human host.
Lower temperatures (17-18 degrees Celsius) result in longer incubation period thereby leading to decreased virus transmission. With increasing temperatures, feeding increases because of enhanced metabolism of the mosquito, leading to shorter incubation period. Even a five-day decrease in the incubation period can hike transmission rate by three times, and with an increase in temperature from 17 to 30 degrees Celsius, dengue transmission increases fourfold, the results showed.
The researchers observed that except for Gujarat which comprises of arid regions, there was a strong correlation between rainfall and dengue disease burden. An increase in breeding grounds for mosquitoes could be a major reason for this finding, according to the researchers. The study found that Kerala being warm (temperature range 23.5-30 degrees Celsius) and wet and with short incubation period (9-14 days) experiences the highest number of dengue cases.
Findings published in the journal Emerging Microbes & Infections showed that as incubation period is shortest during monsoon, chances of dengue are higher during that season. This climate-based dengue forecasting model can assist health department in evaluating the intensity of disease in a particular geographical region. This would further help them to plan disease control methods in advance and enhance optimisation of resources available.
(With IANS inputs)