Expert points out that unfortunately immunity against dengue is not complete as there are four serotypes for this virus.
Representative image (Wikimedia Commons)
Over 8,000 cases of dengue have been reported so far in Kerala in 2024. In the last week alone, the state has reported 774 cases of dengue according to the health department.
As of 30 June, health department officials have confirmed around 8,004 dengue cases and 22 deaths. Additionally, there have been around 21,045 suspected dengue cases and 51 suspected dengue deaths reported.
Last month, during the period of torrential rain from 1 to 30 June, there were approximately 2,207 confirmed dengue cases and four confirmed deaths. In the same period, 6,711 suspected cases and 13 suspected deaths were reported.
It should be mentioned that according to the Union Health Ministry, Kerala reported 17,426 cases of dengue and 153 dengue deaths in 2023.
The symptoms of dengue include high fever, severe headache, pain behind the eyes, joint and muscle pain, rash, and mild bleeding (such as nose or gum bleeds, or easy bruising). Severe dengue (also known as dengue hemorrhagic fever) can cause bleeding, blood plasma leakage, and organ impairment. The most severe form, dengue shock syndrome, can lead to shock, coma, and death.
The incubation period for dengue is typically 4-10 days after the bite of an infected mosquito.
According to the health department, On 30 June, the state reported 55 confirmed cases of dengue. On 29 June, there were 139 confirmed cases and one death, with most cases coming from Ernakulam (54). Similarly, on 29 June, there were 101 cases, with Ernakulam accounting for 35 of them.
On 27 June, there were 108 cases, mostly from Ernakulam (35). On 26 June, there were 182 cases, with Ernakulam reporting 74 of them.
On 25 June, there were 114 cases and one death, with Ernakulam reporting the most cases (26). On 24 June, there were 75 cases, with 42 from Ernakulam. On 23 June, there were 38 cases, with most cases from Ernakulam and Alappuzha (9 each). On 22 June, there were 93 cases and one death, with most cases from Ernakulam (29).
Dengue is caused by the dengue virus, which is transmitted to humans through the bite of infected Aedes mosquitoes, primarily Aedes aegypti and Aedes albopictus.
Once the monsoon starts, high moisture content in the air creates an environment where harmful microorganisms thrive, increasing the transmission of diseases through mosquitoes, water, air, and contaminated food.
Aedes aegypti and Anopheles mosquitoes, known for transmitting dengue and malaria, lay their eggs in stagnant water. Heavy rain leads to water accumulation in containers, puddles, clogged drains, and other areas, providing perfect breeding grounds for mosquitoes.
“Dengue is caused by a virus that is spread by Aedes mosquitoes which lay eggs in freshwater and have a habit of biting people aggressively during the day. As the monsoons arrived towards the end of May, the eggs that were laid in summer hatched and millions of young adult mosquitoes came out,” IMA Kerala’s public health advisory panel member, Dr Rajeev Jayadevan told South First.
He added that several countries, especially in South America have had a severe dengue season in the past couple of years and that the same trend is observed in Kerala.
High humidity levels extend the lifespan of mosquitoes, allowing them more time to breed and spread diseases. Mosquitoes are more active and feed more frequently in these conditions, increasing the likelihood of disease transmission.
“Kerala has innumerable freshwater bodies that are a haven for mosquito breeding. In addition, urban areas with busy construction sites are prone to water-logging, which aggravates the problem,” said Dr Jayadevan.
During monsoons, people often spend more time indoors thinking that mosquitoes can bite them outside, but mosquitoes can breed unnoticed in domestic containers, increasing the likelihood of bites. He pointed out that, unfortunately immunity against dengue is not complete, because there are four serotypes for this virus.
Dengue fever is caused by one of four dengue viruses—DENV-1, DENV-2, DENV-3, and DENV-4. The fact that there are four different strains of the dengue virus means that a person can be infected up to four times in their lifetime. Each subsequent infection weakens the immune system and increases the severity of the illness. Experts fear a surge in dengue cases is overdue.
Each of these viruses has a different serotype, which is a specific strain of the virus. When a person is infected with dengue, their immune system develops antibodies to the specific serotype they were infected with.
“Therefore a person who had a dengue episode with one serotype could readily get infected by another. And when that happens, the risk of severe disease increases. With no known antiviral drugs, dengue treatment remains largely supportive, and sometimes, deaths occur,” said Dr Jayadevan.
However, these antibodies do not provide lifelong immunity to all serotypes of dengue. Instead, immunity to one serotype is usually short-lived, lasting only about 2-3 months.
This means that a person can get infected with dengue multiple times, especially if they are exposed to different serotypes of the virus.
Based on the health department’s assessment, intermittent rain, use of contaminated water, and lapses in pre-monsoon cleaning are the primary causes of the spread of such infectious diseases.
Kerala has been experiencing heavy rain for the past few weeks. On Sunday, 30 June, the Indian Meteorological Department (IMD) issued a yellow alert for three districts—Kannur, Kozhikode, and Kasaragod. The alert continued for Kannur and Kasaragod on 1 July, with forecasts of isolated heavy rain in these districts.
The state has also seen a surge in other mosquito-borne diseases, with 21 H1N1 cases and 127 leptospirosis cases reported in the same period. Factors contributing to the rise in dengue cases include intermittent rainfall, improper waste management, and lapses in pre-monsoon cleaning efforts by local authorities.
Since April 2024, the global genome sequencing of the dengue virus has shown that Dengue serotype 1 genotype V accounts for 47 percent of cases, while Dengue serotype 2 genotype Cosmopolitan II makes up 38 percent of cases. Other serotypes and genotypes constitute the remaining 15 percent.
According to GISAID, no data has been collected from India since November 2023. In 2023, the most common variant in India was Dengue serotype 2 cosmopolitan II, which accounted for 68 percent of the cases.
(Edited by Neena)
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