Possibility of next epidemic may be more virulent

Kerala could be bracing for yet another major dengue epidemic in 2020 going by the current and early disease surveillance trends.

With serological evaluations showing that there might be a shift in the type of dengue virus hitherto circulating in the community, the possibility of the next outbreak being more virulent, with significant mortality, cannot be discounted, public health experts have warned.

Not just dengue, Chikungunya (CHK) also seems to be rearing its head again, with a significant spike in the number of cases being reported from Thiruvananthapuram.

After 2007-09, Chikungunya has not been a major issue in the State as a significant section of the community had been rendered immune due to natural infection.

However, CHK cases could be spiking now because the threshold of herd immunity rendered by the natural CHK infection is beginning to wane.

Cyclical pattern

Dengue epidemics occur in a cyclical pattern and the last major epidemic in 2017 resulted in 21,993 cases (lab confirmed alone) and 165 deaths.

“Dengue pattern in the State over the years shows that cases usually spike in July-August. But whenever cases have spiked in November-December, it has been followed by major outbreaks in the subsequent year, as was true in 2013 and 2017 when the State had major epidemics. In December 2013, 90 cases and in 2017 same month, 86 cases were reported. This year, in the first one week of December itself, 147 confirmed and some 210 suspected dengue cases have been reported, especially from Thiruvananthapuram and Ernakulam,” a senior public health professional said.

Virological switch

What is more worrying is that there seems to be a virological switch or a change in the predominant type of dengue virus circulating in the community this time.

Dengue virus type 2 (DENV 2) is the commonest circulating dengue virus in the State, accounting for nearly 50% of the infections in all outbreaks. The 2017 outbreak was severe because there was a significant percentage of type 1 (DENV1) cases.

“We had sent 40 blood samples of dengue positive cases last month for serological analysis at the ICMR’s Virus Control and Research Centre at Kottayam. To our surprise, 35% of the cases were of type 4 (DENV4), which has been the hardest to find in the State so far. Type 4 has probably come across Tamil Nadu border. Going by the epidemiological and virological patterns, we fear that the State is in for a major outbreak, next year, unless serious and sustained control measures are launched immediately,” a senior public health expert told The Hindu.