SINGAPORE - Dengue cases are on the rise again, with infections from the DenV-3 and DenV-4 serotypes accounting for over half the cases since February.
The Straits Times looks at what this means, and the measures being done for infection control.
Q: Is it true that I will have more serious illness if I get dengue a second time?
A: Professor Paul Tambyah, president of the Asia-Pacific Society of Clinical Microbiology and Infection, said dengue reinfection is dangerous when a patient is infected with a different dengue serotype the second time round.
A person who recovers from DenV-1 dengue would develop antibodies which protect against most DenV-1 infections, but not DenV-2.
"So if some people are infected with DenV-2 some time after a DenV-1 infection, there is a risk that the immune system ends up overreacting instead of destroying the DenV-2 serotype," he said.
Professor Lok Shee Mei from Duke-NUS' Emerging Infectious Diseases (EID) programme said there are different virus strains within each serotype, and each strain can exhibit vastly different shapes, enabling them to escape detection by the immune system.
For example, it was found that the DenV-3 serotype is able to transform its shape from a round particle into a club-shaped one to evade immune response, making it difficult to develop therapeutics or a vaccine for it, she said.
Q: Are there any vaccines against dengue and are they safe?
A: Currently, only the Dengvaxia vaccine, which is said to be able to prevent dengue caused by all four strains of the virus (DenV-1, DenV-2, DenV-3 and DenV-4), has been approved for use.
However, it is safe for use only in those who were previously infected with dengue. Those who have not been infected before could be at risk of severe disease.
This is because the vaccine works by priming the immune system and acts as a first infection, said Prof Tambyah. However, as the vaccine is not powerful enough against all four strains of dengue, it could therefore lead to an immune overreaction during a subsequent dengue infection.
Hence, it is recommended that those looking to take the Dengvaxia vaccine go for a serology test first to ascertain if they have had a past dengue infection.
Prof Lok said an effective vaccine has to be able to stimulate equally strong protective responses simultaneously against all four serotypes.
She added that clinical trials of a vaccine by pharmaceutical giant Takeda has so far shown encouraging results.
EID researchers are also aiming to develop a cocktail vaccine taking into consideration the different DenV morphologies, said Prof Lok.
Q: What is the National Environment Agency (NEA) doing to help prevent the spread of dengue?
A: Since March, together with the Inter-Agency Dengue Task Force, NEA has started an exercise to remove potential mosquito breeding habitats, ahead of the traditional peak dengue season.
NEA's dengue prevention volunteers and grassroots advisers have also visited homes in dengue clusters and areas with a high Aedes aegypti mosquito population to advise residents on dengue prevention.
Field trials for Project Wolbachia are also ongoing, NEA said.
This project involves releasing sterile male mosquitoes in certain areas in Singapore. Female Aedes aegypti mosquitoes that mate with such males lay eggs that do not hatch, thus suppressing the mosquito population.
The mosquitoes will be gradually released in the whole of Yishun and Tampines towns by early next year.