Public health experts have called for close monitoring and surveillance of dengue cases admitted in hospitals for possible change in clinical patterns, like unexpected liver failure, as a switch in circulating dengue virus (DENV) serotypes could lead to a severe outbreak this season.
In fact, epidemiologists who have been closely following the evolution of the circulating dengue virus types in the State since 2017 think that the DENV shift or switch might have already happened because 70% of the dengue case samples studied in 2022 in Thiruvananthapuram district were DENV3 serotype and some of the samples, DENV4.
All four in Kerala
Kerala is hyperendemic for all four serotypes of DENV since the past two decades or more, meaning that all four serotypes are in circulation in the State throughout the year. Historically, however, surge in cases has usually been due to DENV1 and DENV2. There has been a shift in this pattern since 2019, according to researchers who studied the epidemiological and clinical characterisation of DENV serotypes in two districts in southern Kerala from 2017-2019. (Rahul A et.al, Epidemiological and clinical characterization of dengue virus serotypes during 2017-2019 in southern Kerala, India. Trans R Soc Trop Med Hyg. 2022 Oct 2).
They reported that while in 2017, DENV1 and DENV2 were the predominant serotypes, there was a marked increase in the proportion of DENV4 cases (34.56%) in 2019.
They noted that DENV3 infections were more likely to present with warning signs and a significantly lower platelet count. The study warned that the changing pattern of dengue virus predominance and the rise in DENV4 put forth the possibility of a more severe future outbreak.
Similar in Singapore
Singapore is one nation which, like Kerala, experiences dengue epidemics in a cyclical pattern every three or four years. Every time there is a switch in the circulating DENV serotype, the outbreaks have been more severe. In January 2020, Singapore’s virological surveillance system detected a shift from DENV2 to DENV3, a serotype which had not been detected in the country in the past 30 years. Despite all precautionary measures, Singapore had its worst dengue epidemic till date in 2020.
“Kerala too had two major outbreaks in a cyclical pattern in 2013 and 2017. Though we expected a repeat in 2021-22, probably because of the restrictions on movement and activities imposed by the pandemic, dengue spread was manageable then. But a switch from DENV1 and 2 to DENV3 and 4 could certainly indicate that we may be in for a major outbreak. This could mean a surge in case numbers or an increase in case severity,” says T.S. Anish, Additional Professor of Community Medicine, Government Medical College, Manjeri.
Asymptomatic
Nearly 80% of dengue infections are usually asymptomatic (“inapparent dengue”) and these sub-clinical infections in the community go untested as these are taken for simple viral fever. A dengue infection confers lifelong immunity only to that particular serotype and temporary cross-immunity against other serotypes. Once this cross-immunity wanes, a second infection by a different serotype can trigger severe immune response in the body, leading to severe and life-threatening conditions such as dengue shock syndrome or haemorrhagic syndrome.
A study published in the Lancet in July 2019 on the burden of dengue infection in India puts the overall seroprevalence in the country at 48.7%. The seroprevalence in the southern region was the highest at 76.9%. This means that three-fourth of the population in the south have already been infected by at least one dengue virus serotype and stands the risk of a severe secondary infection.
Immediate medical care
“This is the time for improved clinical surveillance, alongside virological surveillance. Attention should now shift to patients admitted in hospitals, for vigilant monitoring for any changes in clinical patterns. Picking up early warning signals can initiate appropriate management and reduce dengue mortality. People should seek immediate medical attention if they have fever symptoms. Dengue can be detected as soon as symptoms show up, through testing modalities like Dengue NS1 Antigen,” a senior public health expert said.
