The spread of dengue fever and other tropical diseases

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In Singapore, a watchful eye is kept on stagnant water. Ground puddles, water containers, clogged drains, toilet bowls, and discarded pails are all carefully monitored by the Government. But why? These sites create favorable conditions for mosquitoes to breed, mosquitoes that carry around dengue fever – a viral infection that has no cure, and in rare occasions, is fatal. The Singapore dengue control programme is committed to clamping down on the issue with a focus on removal of water containers from in and around homes, solid waste management, and limited use of insecticides (1). But they are fighting against an external factor that can not be overcome without global collaboration: climate change.

Warmer temperatures are speeding up the replication of dengue fever virus. And Oman is just one of the countries that has felt the effects of climate change on vector spread in recent years. We spoke with Jorge Abarca, an infectious disease consultant working in Oman, to discuss the importance of international collaboration in combating the spread of infectious disease, future innovations in dengue disease management, and how we can take a leaf out of Singapore’s book.

In simple terms, how does climate change contribute to the spread of infectious disease?

Climate change is a contributor to the expansion and dissemination of vector-borne diseases. A combination of rising temperatures, altered rainfall patterns, and an increase in humidity create ideal breeding conditions for disease vectors. Increased rainfall also creates more breeding sites for mosquitoes – especially in urban areas.

In your presentation at RCPath 2023, you said cases of dengue fever have gone up in Oman, why is this the case? And why is this particular disease such a concern?

Well, I’m concerned about all infectious diseases! But yes, the spread of dengue fever is particularly alarming. In previous years, dengue fever has not been endemic to Oman. But recently, I was given the official numbers from Oman’s Minister of Health. In 2020, there were 300 cases; in 2021, there were 24 cases; and in 2023, there were 1989 cases of dengue fever. So the number of cases drastically increased. What happened?

During these years – although the COVID-19 pandemic wasn’t at its highest level – other diseases were effectively put on the back burner. They were not being monitored as closely, and it’s likely that many positive cases were not properly diagnosed during this time. When COVID-19 cases decreased, and people started coming out of isolation – that’s when the cases drastically increased. A similar pattern can be observed with influenza. The WHO showed how common flu cases decreased during the pandemic. This is because everybody isolated, so it was spread less, but also because many cases remained undiagnosed.

But there is the case of climate change, too. In 2022, the temperatures exceeded 40 °C in Oman, and seasonal monsoons (Khareef) brought heavy rains and cooler temperatures, especially in the Dhofar region. Oman lacks a proper drainage system, so flooding is usually extreme. This, of course, increases the water deposits that mosquitoes are attracted to. From a governmental perspective, there was not a proper implementation of programs for awareness, education, and detection of dengue fever. Healthcare workers were solely focused on COVID-19, so the increase in cases came as a surprise to everyone.

Credit: image supplied by Jorge Abarca

Meet Jorge Abarca

I’m a Spanish infectious disease consultant working and living in Muscat, Oman. I am currently head of the infectious disease division and chair of the infection prevention and control committee at Sultan Qaboos Comprehensive Cancer Care and Research Centre. I oversee the antimicrobial stewardship program as its champion, conduct infectious disease consultations, and implement strategies to engage the infection prevention and control measures within our hospital – a cancer center that only opened in 2021. We’ve received great feedback from the population and from other hospitals, which is amazing after starting it from scratch.

Vector cycles are shortening – what could this mean for disease spread?

The normal cycle of a vector could take about three days. However, because of climate change and an increase in water temperature, cycles are taking only 24–36 hours, which leads to larger populations. Consequently, we have more vectors in a significantly reduced space, making it easier to transmit infections – a sort of domino effect.

Considering the global nature of climate change, how important is international collaboration in combating the spread of infectious disease?

International collaboration is indispensable in addressing the global impact of climate change on infectious disease. We need a collaborative effort to facilitate the sharing of research findings, resources, and expertise.

Local organizations can also contribute by raising awareness and providing proper education and information. We learnt so much from COVID-19 – the general population was amazing. The fact that everybody – given the proper information – isolated for months is no small feat. If we applied this effort and commitment to climate change action, the impact would be huge. Margaret Mead once said, “Never doubt that a small group of thoughtful, committed citizens can change the world; indeed, it’s the only thing that ever has.” It couldn’t be more true!

Credit: image supplied by Jorge Abarca

What more could be done to raise awareness of neglected tropical diseases risk?

We need more educational campaigns involving healthcare professionals – primary care physicians and GPs can all play a role. Given that Oman is a Muslim country, health care and epidemiology education provision at every single mosque could have a great impact. Social media can also help disseminate information – especially to younger generations who are generally less committed to climate change initiatives. Finally, collaboration with NGOs and governmental agencies can help reach diverse populations and more rural areas. Spreading awareness needs a multisectoral approach.

What future innovations can we expect to see in dengue disease management?

Right now, artificial intelligence (AI) is a hot topic everywhere. In the realm of disease management, we can, for example, design algorithms to combine different aspects of climate change – humidity, rainfall, and high temperature data – to predict by how much vectors could increase.

We also need continuous monitoring and surveillance. For instance, integrating satellite imaging to monitor environmental changes and predict potential dengue fever hotspots. This activity should be supplemented with community-based surveillance, which helps foster a proactive approach to outbreak prevention.

Future innovations in the pharmaceutical sector could be a fantastic contribution. COVID-19 showed us how effective vaccinations could be developed in a short amount of time. The current vaccine for dengue fever is only 40–70 percent effective, depending on very specific serotypes. But the next generation of vaccines can be better. We need to reduce the cost and increase the coverage – especially in endemic areas.

What steps need to be taken to prevent mosquito borne diseases spreading?

Using the proper insecticides and biological control agents will help. But we also need to tackle the problem as a community. How? Mosquitoes require water and high temperatures for reproduction. By reducing the number of water containers on the streets or outside our homes, we can decrease mosquito breeding. Singapore, for instance, follows a stringent protocol, especially during the rainy season, where fines are imposed if water containers outside houses are not controlled. The government consistently encourages public awareness. Collaboration between the general population and the government can lead to significant progress.

What policy recommendations do you think are essential at both national and international levels to address the rising threat of neglected tropical diseases in Europe?

First, there needs to be global acceptance that climate change is real. Currently, we have some big nations who are in complete denial. It is an undeniable situation in our world. All the big nations and their health departments need to act – and fast. We need to increase research, increase funding, and increase education. We also need to implement proper policies for recycling and trash removal. All this may sound easy, but it is very complicated; everybody needs to be involved – at every level of society. Politicians need to be convinced. We need to create funds. As I have highlighted before, a multisectoral approach is paramount!

The risks of failing to act are very real. It’s not only dengue fever that is exacerbated by climate change; there is also Zika virus, Chikungunya virus, and many other mosquito-borne diseases. But it’s not just viruses we have to worry about. In the US, Lyme disease is increasing because of climate change. And if you like raw oysters, I can offer a final example; Vibrio bacteria like to accumulate in oysters and the higher the coastal water temperature, the higher the risk. It almost goes without saying that there is nothing aphrodisiacal about vibriosis.

Click here to read Part II of this article