Authors: Alice Greenway, Future Science Group
An international team of researchers have successfully identified the key climatic parameters for predicting dengue virus outbreaks by tracking disease progression through the different climatic zones of India.
The study, which was held in India, was part of an international collaboration between scientists at the University of Liverpool (UK) and the Hyderabad-based Indian Institute of Chemical Technology (IICT), National Institute of Pharmaceutical Education and Research (NIPER; Guwahati, India).
“This climate-based dengue forecasting model could help health authorities to assess the disease intensity in a geographic region, based on that they can plan disease control operations well in advance and optimize the use of resources meticulously” explained the lead researcher, Srinivasa Rao Mutheneni, of IICT.
Researchers focused on evaluating how climatic conditions influenced a factor named the ‘extrinsic incubation period (EIP)’ of dengue virus.
The EIP represents the time period between the mosquito taking its first viremic blood meal, the virus escaping the gut, entering the salivary glands and therefore becoming infectious – also understood as the viral incubation period.
Dengue is driven by complex interactions among vector, host and virus and it has been reported that climatic parameters play a key role in determining the EIP.
In this study, the EIP was calculated for different seasons in the states of Punjab, Haryana, Rajasthan, Gujarat and Kerala (all India).
Researchers discovered that lower temperatures (17–18°C) correlated with longer EIPs and therefore reduced virus transmission. With increasing temperatures however, mosquito feeding increases, in line with an enhanced metabolism, leading to decreased EIPs and faster transmission.
Even a 5 day reduction in EIP can amplify dengue transmission rates by three-fold, and at a peak temperature of 30°C transmission rates can hike to a devastating four-times the average rate for 17°C. Conversely, a surge in temperature exceeding 35°C is detrimental to the survival of the mosquito.
The researchers also observed a significant association between precipitation and dengue disease burden in all states, except for Gujarat which is mainly comprised of arid regions. The team hypothesized an increase in rainfall was associated with a higher number of breeding grounds for mosquitoes.
Among the studied states, Kerala had the highest dengue disease burden and the lowest mean EIP (8–15 days) due to its high temperature, wet climate (ranging from 30.8–23.4 °C).
In support of this, researchers found that out of all seasons, monsoon season carried the most risk of dengue disease outbreak.
The prevalence of dengue cases has substantially increased in India since 2001 and epidemics have become more frequent. This climate-based dengue forecasting model could provide an important tool for assessing disease burden and implementing control strategies.
Rao expanded: “Though such methods are in vogue for disease control operations, we are still in the initial stages of implementation of such strategic control methods. Factors such as population density and migration also need to be included for future risk assessment studies.”
Sources: Mutheneni SR, Morse AP, Caminade C, Upadhyayula SM. Dengue burden in India: recent trends and importance of climatic parameters. Emerg. Microbes Infect. doi:10.1038/emi.2017.57 (2017); https://news.liverpool.ac.uk/2017/09/01/new-method-developed-to-forecast-dengue-disease-spread/