The dengue graph is rising in Kerala and Health officials fear that the State could be in for yet another tough season of infectious diseases this year. The State has reported an uptick in dengue cases in the past few weeks. On Wednesday, 105 cases were reported and on Thursday, 68 dengue cases and one death.

So far, 3,565 confirmed and 10, 428 probable cases of dengue have been reported in the State. Almost 57% of cases were reported in May (928) and June (1,097 as on June 18). Dengue has so far claimed 17 lives this year and another 15 deaths are also considered as probable dengue deaths.

Health officials said the monsoon rainfall had been playing truant and that the pattern of intermittent rainfall followed by warm spells could lead to an explosion in vector indices in the coming weeks. On the other hand, sustained heavy rainfall could wash away mosquito breeding sites.

Dengue fever has been a persistent public health challenge in Kerala, with cyclical outbreaks, serotype shifts, and seasonal spikes tied to monsoon patterns. Kerala is a hyperendemic State for dengue, with all four dengue serotypes circulating through the year. However, the pattern of cyclical major, severe outbreaks makes the State a textbook case of serotype-driven outbreak dynamics.

Various strains

Epidemiological studies in the State have shown that dengue infection in Kerala is largely contributed by DENV 2, which is the dominating strain elsewhere in India too. A significant number of cases are due to DENV 1. Kerala had two major outbreaks in a cyclical pattern in 2013 and 2017. The large outbreak of 2017 was due to the emergence of DENV 1 strain in an endemic situation which was dominated by DENV 2 strain.

The outbreak in 2017 was one of the worst recorded dengue epidemics with 21,993 confirmed cases and 165 deaths. The number of probable cases was 66,329. In subsequent years, cases due to DENV 4 strain and more recently, DENV 3 strain cases have also seen a rise.

Dengue had shown a surge in 2023, with 16,766 confirmed cases and 153 deaths. The trend continued in 2024, with 20,674 confirmed cases and 128 deaths. In comparison, 2025 turned out to be a better year, with the State recording 10,865 cases and 56 deaths. Nearly 80% of the dengue infections are sub-clinical or asymptomatic and these infections are often treated as simple viral fever.

Danger of secondary infection

What makes dengue dangerous is the secondary dengue infection, because of the phenomenon called antibody-dependent enhancement. A dengue infection confers lifelong immunity only to that particular serotype and a subsequent infection by a different circulating sero type can lead to a cascade of immune responses in the body, leading to severe shock syndrome or haemorrhagic syndrome.

This is why every time there is a shift in the circulating sero type, major outbreaks with increased case severity occurs. Continuous sero type surveillance in the field is thus crucial for outbreak prediction and preparedness. Public health experts maintain that close monitoring and surveillance of dengue cases admitted in hospitals are necessary every season so that possible changes in clinical patterns, like unexpected liver failure, can signal the outcome of a possible sero type shift.