Preventive drugs may be needed to fight dengue outbreaks: Experts

There is currently no specific antiviral drug against dengue for the general population, but clinical trials are being conducted. ST PHOTO: LIM YAOHUI

SINGAPORE - Preventive drugs have been found to be effective in controlling the spread of malaria, and experts now say they may be needed to fight dengue outbreaks as well.

Coupled with the use of data science to predict large clusters, they could help to combat the Aedes aegypti mosquito threat in Singapore, said Professor Martin Hibberd from the London School Of Hygiene and Tropical Medicine.

"We've seen that malaria drugs have been effective in preventing the spread of the disease in Haiti.

"Given that the dengue drug uses the same mechanism, it should also be applicable for controlling dengue outbreaks," said Prof Hibberd.

The infectious diseases expert was in Singapore, where he spoke at the 5th Asia Dengue Summit held at Orchard Hotel on June 15.

The United States' Centres for Disease Control and Prevention lists two preventive drugs, or prophylactics, that travellers could take to prevent malaria.

"This approach of taking preventive medication - in the case of malaria - is currently dispensed to travellers but not one that has been used in Singapore, where mosquitoes and dengue are found endemically.

"As controlling the chain of dengue transmission within a household or community is highly time-sensitive, using these prophylactics could help extend that time frame, especially since several days often pass before people present symptoms of dengue infection," added Prof Hibberd.

A study by researchers from the London School Of Hygiene and Tropical Medicine, using datasets from Singapore, suggested preventive medication could play a role in dengue control.

The scientists, whose paper was published last year, said when applied in areas that have recently experienced cases of disease, prophylactic drugs could be more effective than adult mosquito-killing vector control methods.

They could even offer the possibility of interrupting individual chains of transmission if rapidly deployed.

Researchers in Singapore are currently conducting clinical trials on a drug made by Belgian drug manufacturer Janssen Pharmaceuticals.

The new experimental drug works by preventing two proteins from the dengue virus - known as NS3 and NS4B - from interacting, similar to the mechanism used by malaria drugs.

Singapore is currently in the middle of a huge dengue wave, with more than 15,000 cases reported in the first 24 weeks of this year.

Professor Leo Yee Sin, executive director at the National Centre for Infectious Diseases, said there is currently no specific antiviral drug against dengue for the general population.

The overall treatment is to tackle the symptoms, which the Ministry of Health lists as fever, skin rashes, severe headache, nausea and vomiting, and mild bleeding.

Prof Leo said the current approach on dengue management in Singapore focuses on community awareness, and seeking early medical attention to achieve early diagnosis.

But Professor Tikki Pang, former director of research policy and cooperation at the World Health Organisation, called for wider use of the Dengvaxia vaccine among seniors in a forum letter to The Straits Times last month.

It is a vaccine used for the prevention of dengue disease caused by four specific strains of the dengue virus (serotypes 1, 2, 3 and 4), according to the Health Sciences Authority (HSA).

Professor Martin Hibberd speaks during the 5th Asia Dengue Summit at the Orchard Hotel, on June 15, 2022. PHOTO: ASIA DENGUE SUMMIT

Prof Leo said the vaccine is approved for use in patients aged 12 to 45 who have previously contracted dengue, and added that its use is limited among the elderly who in general suffer higher risk of severe illness and mortality.

Prof Pang, a visiting professor at the Lee Kuan Yew School of Public Policy, noted that Dengvaxia is not recommended for those who have not had dengue infection before because of an increased risk of hospitalisation for dengue and severe dengue.

"In my considered view, this caution may not apply as much to the elderly above 65 who, because of their age, would have been exposed to the dengue virus before in their younger years, or might actually have had dengue with no or mild symptoms.

"And because older people are at higher risk of severe dengue and death, I feel the judicious use of the vaccine - with a check for previous infection - for this segment of the population can add significantly to the tools we have to fight dengue," he said.

Prof Hibberd said that in addition to preventive medication, it is also possible to use predictive data models such as the one developed by the National Environment Agency's (NEA) Environmental Health Institute and the NUS Saw Swee Hock School of Public Health to pre-empt outbreaks.

The model can predict dengue case trends up to three months ahead.

Aside from data science, NEA also uses a network of gravitraps - designed to attract and trap female Aedes adult mosquitoes that are looking for sites to lay their eggs in - to provide surveillance of mosquito populations.

The London School Of Hygiene and Tropical Medicine researchers, who were supervised in their study by Prof Hibberd, had also developed predictive data models.

When used in tandem with preventive medicine, they said it could aid in targeting interventions to contain the outbreaks of dengue.

Meanwhile, with June being the start of the traditional peak dengue season, Singapore is bracing itself for a record high in weekly dengue cases, which may exceed 2,000 cases this month.

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