Preventing dengue before any cases occur

A sheltered wall in an apartment complex being sprayed with insecticide during the targeted outdoor residual spray part of the programme. — Photos: Bayer

The global incidence of dengue has increased 15-fold over the last two decades, despite numerous interventions and strategies put in place to combat this infectious disease.

The Asean Dengue Day, which is commemorated on June 15 every year, serves as a reminder of the importance of controlling and preventing the illness or life-threatening disease caused by dengue, which roughly half the world’s population is at risk of today.

Dengue is a mosquito-borne viral disease threatening communities in more than 100 countries.

It is caused by four closely-related viruses named DEN-1, DEN-2, DEN-3 and DEN-4.

These four viruses are called serotypes because each has different interactions with the antibodies in human blood serum.

No cure currently exists for dengue, making it crucial for proper vector control to help combat this disease spread mainly by the female Aedes aegypti mosquito.

Preventing or reducing dengue virus transmission depends entire-ly on controlling the mosquito vectors or interrupting human-vector contact.

With health systems and hospitals across the globe often strained during the current Covid-19 pandemic, there is a need for increased focus on eradicating the threat of preventable vector-borne diseases.

According to the World Health Organization (WHO), dengue cases have been on the rise in Malaysia since April (2020), similar to last year’s trend.

Health Minister Datuk Seri Dr Adham Baba had also said in a statement in conjunction with Asean Dengue Day (2020) that the ministry is expecting a rise in dengue fever cases starting in early June until September.

A new approach

With this in mind, the Intervention for Dengue Epidemiology in Malaysia (iDEM) programme, a first-of-its-kind collaboration among public hospitals, universities, research centres and non-profit organisations, kicked off earlier this year (2020).

It seeks to demonstrate a link between innovative prevention measures and a quantified, reduced rate of dengue occurrence.

iDEM is focused on reassessing a traditionally reactive approach to treating dengue and other vector-borne diseases and instead, demonstrating the effectiveness of on-going management programmes that are grounded in prevention.

Led by the Health Ministry and supported by Bayer and other world leaders in public health, such as the Innovative Vector Control Consortium and In2Care, the iDEM programme is expected to continue through 2022.

By pooling knowledge, expertise and tools, the consortium has put a proactive integrated vector management system (IVM) in place.

In response to increasing resistance to insecticides used in vector control, iDEM’s integrated approach uses both chemicals and biologicals with different modes of action, targeting various mosquito life-cycle stages.

This preventive approach is not only beneficial from a public health perspective, but also in terms of public funding.

The estimated economic toll imposed by dengue in Malaysia alone amounts to a staggering US$102mil (RM433mil) per year.

When direct costs (such as hospital services) and indirect costs (such as productivity losses and premature deaths) are lowered through a focus on prevention, rather than reactive treatment methods, the amount of public funding needed to combat dengue is expected to dramatically decrease.

Dr Rose (second from right) inspecting the auto dissemination devices in the field with members of the iDEM consortium, including Dr Saadatian-Elahi (right). Dr Rose (second from right) inspecting the auto dissemination devices in the field with members of the iDEM consortium, including Dr Saadatian-Elahi (right).

Three components

According to iDEM project leader and France’s Hospices Civils de Lyon epidemiologist Dr Mitra Saadatian-Elahi, some of the determinants of dengue are urbanisation and poor sanitation.

The majority of cases can be prevented by vector control programmes that are guided by local conditions.

“Such programmes are highly effective in reducing the density of the Aedes population, but proof of their efficacy in reducing incidence of Aedes-borne disease is limited.

“iDEM was based on locally adapted and sustainable vector control programmes that combine insecticides with different modes of action.

“Since Malaysia is a hotspot for dengue and has a state-of-the-art digital dengue reporting system, it is a suitable place to conduct this trial to test the effectiveness of the IVM,” she said in a recent public webinar.

The three components of IVM are:

  • Targeted outdoor residual spraying using K-othrine polyzone (an insecticide), which is sprayed on covered and partly covered walls on all floors of high rise buildings once every four months
  • Auto dissemination devices, which are user-friendly devices that target hard to find areas, and
  • Active community engagement.

“We have chosen 300 localities or clusters in Putrajaya and Kuala Lumpur.

“The area size was calculated to see a reduction of 30% in the incidence of dengue.

“The trial will cover four intervention cycles in two years.

“We hope that by involving the community, we can enhance the IVM, and perhaps shift the policy agenda from treatment to prevention, thus saving public funding.

“The results can then be used in other locations in Malaysia and around the world,” said Dr Saadatian-Elahi.

Community engagement

Elaborating further on the IVM components, iDEM principal investigator and Institute of Medical Research research officer Dr Nurulhusna A. Hamid said that the residual spraying was targeted at semi-indoor areas such as corridors, where mosquitoes like to rest and hide.

“We are targeting high rise buildings in these areas as the mosquitoes are breeding indoors.

“Although we have campaigns to clean up areas for 10 minutes every weekend, I don’t think everyone is doing it – it depends on whether you get infected or not!

“With the auto dissemination devices, we found that this method alone can control and kill infected mosquitoes, but it cannot eliminate the mosquito population, so we have to ensure that there are not enough mosquitoes to transmit the virus.

“We select a place that is slightly hidden from people, to place the devices or traps.”

When the movement control order (MCO) was imposed in March (2020), the community engagement portion of the programme was halted.

But it has since restarted in May (2020), while adhering strictly to standard operating procedures (SOPs).

Dr Nurulhusna said, “Yes, we need to follow SOPs, but that doesn’t prevent us from doing vector control activities on site.

“We spray the wall and put a sticker to inform people not to touch it for an hour. This gives the insecticide time to dry off totally.

“We always have two officers to do quality checks on the people doing the spraying because they need to spray the walls using the right technique.”

The spray formulation protects the active ingredients from weather, rainfall and mechanical abrasion.

It has a three-month residual effect, and is odour-free and safe for both humans and the environment.

“Of the three components, community engagement is the most important, but the challenge is that 2% of the clusters do not have active communities.

“Usually, we won’t have active participation in the first cycle unless people can see some impact in the first cycle.

“The other challenge is to introduce new methods to the public.

“We do this using variable approaches such as social media or SMS, as we need to explain what is happening, why we’re putting the devices, how it works, etc.

“We also have to reduce vandalism on the traps that have been set up as 18% of the traps have been disturbed in various ways.

“This is quite a high rate of vandalism,” she said, adding that the components introduced are not limited to combating dengue, but can be used in controlling other vector-borne diseases as well.

A pilot study to address resistance in mosquito populations conducted in Johor Baru saw samples collected before and after a six-month intervention period.

Sharing the results, Dr Nurulhusna said: “Surprisingly, the baseline showed that the mosquito population was resistant to two clusters of the insecticide.

“Then we did targeted spraying, along with auto dissemination, for eight months and we found that the mosquitoes showed a reduction in resistance.

“It showed that with these two components, we don’t need to use as much insecticide, and I foresee iDEM having similar results.”

Community engagement is a crucial part of any plan to prevent dengue. — FilepicCommunity engagement is a crucial part of any plan to prevent dengue. — Filepic

Following SOPs

While there is a vaccine available for dengue, it is not currently approved for sale in Malaysia.

Health Ministry Vector Borne Disease Sector head Dr Rose Nani Mudin said, “Whether there is a vaccine or not, the main objective of vector control is to prevent transmission of the virus.

“Therefore, for us to have an effective measure, we must ensure that the techniques used follow SOPs, and the chemical used is well controlled and monitored to prevent resistance.

“We also have to train our ground staff regularly.

“For an effective vaccine, it must have good efficacy to all serotypes, especially since we have all four serotypes here.”

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Dengue , infectious diseases


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