A team of scientists at the Rajiv Gandhi Centre for Biotechnology who studied the effect of temperature in altering the virulence of dengue virus (DENV) using mice models has found that environmental temperature can play a key role in enhancing the virulence of DENV.
The factors that drive dengue virus evolution and selection of virulent variants are yet not clear. Dengue being a mosquito-transmitted disease, the ability of the causative virus to grow in the cells of mosquito as well as in humans is a critical factor determining viral virulence. Higher environmental temperature shortens DENV extrinsic incubation period in mosquitoes, increases human transmission, and plays a critical role in outbreak dynamics.
“This is the first study which proves conclusively that higher environmental temperature can increase the virulence of dengue virus. DENV cultured at a higher temperature (35° Celsius) in mosquito cells was significantly more virulent than the virus grown at a lower temperature (28° Celsius), said E. Sreekumar, senior scientist who led the research.
The study titled ‘Higher-temperature-adapted dengue virus serotype 2 strain exhibits enhanced virulence in AG129 mouse mode’ appeared in the prestigious Federation of American Societies of Experimental Biology (FASEB) journal recently.
In the present study, the effect of temperature on DENV virulence was evaluated using DENV2 strains that were propagated at two different temperatures. The viral strains were subjected to whole-genome sequencing to identify genomic changes.
The only difference between the two virus strains used in the study was the incubation temperature in culture for the last three passages, making them behave differently in mice and also acquire mutations in the viral genome.
The mice infected with the virus cultured at 35° Celsius was virulent and induced enhanced viremia and aggressive disease with a short course, haemorrhage, severe vascular permeability, and death. Higher inflammatory cytokine response, thrombocytopenia, and severe histopathological changes in vital organs such as heart, liver, and kidney were hallmarks of the disease.
Genomic analysis also showed that the high likelihood of acquisition of novel genetic changes that enhance infectivity by the virus variants under higher temperature conditions of growth cannot be ruled out. It means that if there is an extended dry spell with high environmental temperature in the State, we should expect the subsequent outbreak of dengue to be more virulent.
In the Kerala context, we need to do at least an observational study if the dengue spell in October-November, when the ambient temperature is inherently low, is less severe than the outbreaks in June-July and if any new mutations are acquired by the virus in June-July, said Dr. Sreekumar.
