GIS data to draw up risk assessment maps for dengue and chikungunya

Could the rare Kyasanur Forest Disease be spreading to the eastern parts of the country? How does paddy cultivation affect the number of Japanese Encephalitis cases? Could filariasis be found in places previously unknown? Researchers from the Vector Control Research Centre have been using satellite data to answer these questions.
A team at the institute has been using satellite data on soil type, rainfall, crop height, forest density among other parameters to develop geographical, time-dependent and risk assessment maps of several vector-borne diseases such as dengue and chikungunya. Their work not only helps in better predicting outbreaks, it has changed the understanding of where the disease is found.
FILARIASIS
A country-wide transmission risk map of lymphatic filariasis was created researchers from the institute using geographic information system and environmental parameters such as soil texture, altitude, temperature, rainfall and relative humidity. Although a nationwide National Filaria Control Programme was started in the country as early on as 1955, there were 190 dricts that remained un-surveyed to see whether the disease was endemic to these areas.
When the researchers used modelling to create the risk map, they realised that the disease was endemic – causing infection in a geographical area – in 113 of these dricts. “To check the findings, we also conducted ground surveys in around 90 places. We found that the model was extremely accurate. What we found on ground matched the findings of our map 92.8 per cent. This shows the importance of such models. It reduces the need for conducting surveys that are man-power intensive,” said Dr S Sabesan, adjunct professor at the institute.
He said, “These 113 endemic dricts were eventually added under the national programme.” The national filaria programme focuses on controlling the mosquito population and detection and treatment of filarial carriers.
Filariasis is caused parasites transmitted mosquitoes and blackflies. Although most cases are asymptomatic, the most dinguishing symptom of the disease is lymphatic filariasis, also known as elephantiasis – swelling of the legs, arms, and genitals because of the damage to the lymphatic system.
JAPANESE ENCEPHALITIS
The researchers from the institute use spectral signatures – the wavelength of light reflected back to a satellite — from growing paddy crops to predicting the risk for spread of Japanese Encephalitis, a viral infection transmitted mosquitoes that causes inflammation in the brain.
“The biggest predictor for the spread of the infection is the mosquito population. The mosquitoes that spread the infection are actually zoophilic, meaning they prefer biting animals. But when their population explodes, there is a spill-over and some end up biting humans. Every stage of paddy growth has a different spectral signature, so we were able to associate the particular stage of growth with vector abundance. So, if all other factors like presence of host and weather are conducive, we can tell when an outbreak might happen,” said Dr Sabesan.
India reports anywhere between 1,000 and 2,000 cases of the infection every year, with about 200 to 300 deaths, according to data from the National Vector Borne Disease Control Programme. Most of the infections are mild and lead to symptoms such as fever, headache, and vomiting. It can also lead to altered mental status and seizures in some.
The disease came to limelight when more than 60 children in UP’s Gorakhpur died at a hospital facing an oxygen crisis. Incidentally, it was the Puducherry institute that showed most of the deaths were actually caused another mite-borne infection called scrub typhus.
KYASANUR FOREST DISEASE
Keeping its successes with risk-mapping of various diseases, the institute is now set to see whether the rare infection first detected in forests of Karnataka has been spreading north and even in eastern states of the country. KFD is a haemorrhagic fever – a disease that leads to internal bleeding — caused a virus transmitted ticks. Cases of the infection and deaths have been reported from the western states of Karnataka, Kerala, Tamil Nadu, Gujarat, and Maharashtra.
“The change in land use patterns and thinning forests are the best predictors of the prevalence of the infection. Using GIS data we will do risk mapping for the disease to see whether it is expanding towards the north,” said Dr Sabesan. The model will try to determine climate change and other factors which might lead to transmission of the infection in other parts of the country.
Along with the mapping and on-ground verification of the findings, researchers from the institute are about to undertake a project to study whether the disease-causing tick carried the virus across India, including the eastern parts of the country. The project also aims to see whether the people in these regions have been previously exposed to the infection.
“This will be done in mission mode. Other than mapping, all the information that we gather will help us in developing a plan for eliminating the infection. Our researchers will work on developing diagnostics and vaccines against the infection,” said Dr Ashwani Kumar, director, VCRC.