Sporadic Rainfall May Increase Dengue Cases in Ahmedabad, Say Experts

Ahmedabad has recorded less number of dengue cases so far this year, but experts believe that spells of rain can play a pivotal role in deciding how the mosquito-borne disease will behave in October and post that.

Dengue and other vector-borne diseases including malaria, Zika virus, Chikungunya, Yellow fever are spread by bite of mosquitoes that breed in stagnant water.

“More vigilance is required while treating the water or checking for spots of mosquito breeding this year. “This year, the rain is received in periodic spells — even when you carry out sustained drive and eradicate the mosquito eggs, another spell after a few days can revive the remaining ones,” The Times of India quoted Ahmedabad-based epidemiologist Dr. Chitan Desai as saying.

According to an earlier paper ‘Impact of Climatic Fluctuation on Dengue Virus Etiology’ in Journal of Molecular and Genetic Medicine by a team from CHARUSAT in Changa, the outbreak in 2016 from eight centres in Gujarat and had analysed that high number of dengue cases was observed when the difference in day and night temperature is above or equal to 2 degrees Celsius. The authors of the study calculated temperature at four times of the day and had found the difference by subtracting the day’s highest and lowest from the number to derive the figure.

‘In January and March this difference is very less, sometimes below 1 degree Celsius, indicating the role of relatively low night temperature in reducing the dengue instances,’ the paper mentioned.

Two other factors — atmospheric pressure and humidity - were also pointed out by the researchers. ‘The study conducted by other group have shown the large impact of monsoon on dengue incidence, as it is logically connected with the breeding of dengue host in stored rain water. However, In Indian climate, the maximum number of cases was observed post monsoon, suggesting the breeding of vector in stored water in relatively less humid environment,’ mentioned the paper which further added that the most conducive environment is found when the day is warm, night is cool and there is presence of high humidity.

‘The optimal growth rate of epidemics at 33 degree Celsius implied that many dengue-endemic regions would be challenged by increased transmission potential in the future when temperature rises,’ mentioned a study by Joacim Rocklöv and Yesim Tozan published in April, 2018.