India with its vast and diverse geography and landscape, experiences mainly four seasons-winter, summer or pre-monsoon, monsoon and post-monsoon with six distinct climatic zones.
Scientists, in a new study, have evaluated the relationship of climatic factors in the spread of Dengue in different parts of India and suggest the fine tuning of Climate based disease forecast models for the distinct climatic zones.
These mosquito-borne disease cases have been reported since the early 1960s, but there has been a tremendous increase in their number in the last 15 years. Researchers at CSIR-IICT, Hyderabad, NIPER, Assam in close collaboration with scientists at the University of Liverpool, United Kingdom analyzed the effect of temperature and precipitation on the dengue disease burden in various climatic zones of the country, ranging from dengue endemic regions in North (Punjab and Haryana) to West (Rajasthan and Gujarat) and to the South (Kerala).
They studied the changes in extrinsic incubation period (EIP) of the dengue virus by taking into account the daily and monthly mean temperatures in these areas.
The extrinsic incubation period (EIP) is the time taken for incubation of the virus in the mosquito. During this period, after the mosquito draws virus rich blood meal, the virus escapes the gut and passes through the mosquito’s body and reaches the salivary glands. Once this happens, the mosquito is infectious and capable of transmitting the virus to another human host.
The authors suggest that climatic conditions play an important role in this phenomenon. Their findings show that lower temperatures (~17–18 °C) result in longer EIPs thereby leading to decreased virus transmission. With increasing climatic temperatures, feeding increases because of enhanced metabolism of the mosquito, leading to shorter EIPs. Even a 5 day decrease in the incubation period can lead to the transmission rate of dengue increasing by three times, and with an increase i
n temperature from 17 to 30 °C, dengue transmission increases fourfold. However, a further increase in temperature beyond 35 °C, would be detrimental to the mosquito survival.
They also observed that except for Gujarat which comprises of arid regions, there was a strong correlation between rainfall and dengue disease burden. They propose an increase in breeding grounds for mosquitoes as a major reason for this finding.
The study found that Kerala being warm (temperature range 23.5-30 °C) and wet and with short EIPs (9-14 days) experiences the highest number of dengue cases. In their analysis, they observed that EIP is the shortest during the monsoon season in most states and therefore there is an enhanced risk of dengue during this time.
The group led by Dr. Mutheneni at CSIR-IICT suggests that it is very important to take into account the dynamic EIP estimates in different regions in assessing disease burden.
“This climate based dengue forecasting model helps the health authorities to assess the disease intensity in a geographic region, based on that one can plan the disease control operations well in advance and optimize the use of resources meticulously”’ suggests Dr. Srinivasa Rao Mutheneni, lead author of the study.
With changes in temperature affecting the extrinsic incubation period of the virus, future changes in the climate might have a substantial effect on dengue and other vector-borne disease burden in India.
On asked about the applicability of such methods in better disease control, Dr. SR Mutheneni tells India Science Wire,
“Though such methods are in vogue for disease control operations, we are still in the initial stages of implementation of such strategic control methods”.
The study was published in Emerging Microbes & Infections, August 2017 issue.