Four reasons disease-carrying mosquitoes could be spreading to a car tyre near you

Mosquitoes that can carry yellow fever, dengue and Zika are predicted to reach new populations and geographies over the coming decades. What’s driving their spread?

4 May 2023
6 min read
by Ciara McCarthy
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<article> <h1> <span>Four reasons disease-carrying mosquitoes could be spreading to a car tyre near you</span> </h1> <div><p>Mosquitoes that can carry yellow fever, dengue and Zika are predicted to reach new populations and geographies over the coming decades. What’s driving their spread?</p> </div> <ul> <li> <b>4 May 2023</b> </li> <li> <b class="me-2">by</b> <span> <a href="https://www.gavi.org/vaccineswork/authors/ciara-mccarthy" hreflang="en">Ciara McCarthy</a> </span> </li> </ul> <div> <div> <div> <div> <div> <p> </p> <p>Earlier this month, the World Health Organization (WHO) gave a briefing on the rise of three mosquito-borne diseases: dengue, chikungunya and Zika. These viruses have been circulating for decades, but have historically presented a much lower health burden than a more familiar mosquito-borne threat – malaria. So why is the WHO worried about them now?</p> <p>The incidence of dengue and chikungunya has grown dramatically in recent years. Just over 500,000 dengue cases were reported annually in 2000. By 2019, this had risen to 5.2 million. <a href="https://www.gavi.org/vaccineswork/global-warming-means-one-two-us-are-now-risk-dengue">One in two people worldwide are now at risk of the disease</a>.</p> <blockquote> <h2>Human behaviour has been enabling the expansion of these mosquito populations for centuries, via urbanisation, travel and trade. Allow these processes to occur at ever-increasing rates, throw climate change into the mix, and suddenly more than half the world’s population are living in areas at risk of mosquito-borne virus transmission.</h2> </blockquote> <p>Zika incidence has declined since a large outbreak in 2016, but experts are concerned that viral mutations and waning immunity could lead to outbreaks in the future.</p> <p>The WHO is not just concerned about the increasing numbers of cases – we are also seeing outbreaks of mosquito-borne diseases in regions where cases have never been reported before. A handful of dengue and chikungunya cases have been reported periodically in Europe since 2010, but the WHO has warned that high numbers of cases in South America earlier in 2023 could be an indication of what is to come in Europe as summer gets underway.</p> <p>These diseases are expanding into new regions with the mosquitoes that transmit them. By 2050 the yellow fever mosquito, which is responsible for the majority of dengue transmission, could reach as far north as Chicago and Shanghai. Another related species, the tiger mosquito<em>, </em>could live in large areas of France and Germany.</p> <p>So what is driving this spread? It turns out that human behaviour has been enabling the expansion of these mosquito populations for centuries, via urbanisation, travel and trade. Allow these processes to occur at ever-increasing rates, throw climate change into the mix, and suddenly more than half the world's population are living in areas at risk of mosquito-borne virus transmission.</p> <h3>Urbanisation</h3> <p>The ancestors of the current yellow fever mosquito are thought to have lived in forests in sub-Saharan Africa. Their larvae grew in tree-holes and adults survived on the blood of non-human mammals. However, as humans moved into these habitats, the mosquitoes began to adapt. They started to lay their eggs on materials more commonly found in human environments, such as clay or rubber. They also evolved a preference for feeding on humans.</p> <p>Today, the yellow fever mosquito thrives in urban and peri-urban areas, breeding in pools of water that has collected in anything from plant pots and water storage containers to tyres or uncollected rubbish. This means that rapid, unplanned urbanisation without the right infrastructure – like running water or waste collection – to accompany it creates the perfect breeding ground for these killers.</p> <div> <h4>Have you read?</h4> <ul> <li><a href="https://www.gavi.org/vaccineswork/five-key-links-between-climate-change-and-health" title="Five key links between climate change and health">Five key links between climate change and health</a></li> <li><a href="https://www.gavi.org/vaccineswork/climate-change-has-pushed-malaria-mosquitoes-find-dangerous-new-ground" title="Climate change has pushed malaria mosquitoes to find dangerous new ground ">Climate change has pushed malaria mosquitoes to find dangerous new ground </a></li> <li><a href="https://www.gavi.org/vaccineswork/climate-change-threatens-mountainous-nepal-spike-dengue-infections" title="Climate change threatens mountainous Nepal with a spike in dengue infections">Climate change threatens mountainous Nepal with a spike in dengue infections</a></li> </ul> </div> <h3>Globalisation</h3> <p>Dispersal across long distances was enabled by increased international trade. It is thought that the yellow fever mosquito spread to the Americas via ships soon after the Europeans first travelled there, likely via boats involved in the slave trade. The eggs are able to withstand desiccation for long periods of time, enabling mosquito eggs infected with arboviruses to survive the long journey across the Atlantic.</p> <blockquote> <h2>Nowadays trade in second-hand tyres has been associated with the spread of the yellow fever mosquito, as rain water that has collected inside the tyre can provide a welcoming environment for larvae to grow.</h2> </blockquote> <p>Nowadays trade in second-hand tyres has been associated with the spread of the yellow fever mosquito, as rain water that has collected inside the tyre can provide a welcoming environment for larvae to grow.</p> <h3>Human mobility</h3> <p>Movement of mosquitoes can lead to disease outbreaks in new areas, but so can the movement of people. According to the ECDC, cases of dengue are frequently reported in travellers returning from endemic countries, and these could lead to local spread in areas where mosquitoes are present.</p> <p>Following the first ever dengue outbreak in Madeira in 2012, viral sequencing showed that the dengue virus detected there was closely related to viruses circulating in Venezuela at the time. Nearly 16,000 people travelled from Venezuela to Madeira by air in 2012.</p> <p>Emergence of dengue in rural parts of Brazil has been associated with construction of roads connecting these areas to urban hotspots. A study carried out in Pakistan was able to combine climate data with mobile phone data to predict the outbreaks of dengue in new areas.</p> <h3>Climate change</h3> <p>The mosquitoes that transmit dengue, chikungunya and Zika are very sensitive to climate, and so predicting the impact of climatic changes on mosquito populations can sometimes be challenging. When it is warmer, mosquitoes can breed more quickly and the virus can replicate more quickly inside the mosquito, leading to faster transmission.</p> <p>However, it's not as simple as 'higher temperatures means more mosquitoes'. If temperatures get too high, the standing water that these mosquitoes rely on to lay their eggs can dry out. This means other climatic factors such as rainfall patterns can also determine where mosquito populations are likely to flourish.</p> <h3>What can we do about it?</h3> <p>In 2022, the WHO set up the Global Arbovirus Initiative. At the launch event, Sylvie Briand, the WHO Director of Pandemic and Epidemic Diseases, said that "the next pandemic could very likely be due to a new arbovirus."</p> <blockquote> <h2>It’s not as simple as ‘higher temperatures means more mosquitoes’. If temperatures get too high, the standing water that these mosquitoes rely on to lay their eggs can dry out. This means other climatic factors such as rainfall patterns can also determine where mosquito populations are likely to flourish.</h2> </blockquote> <p>If 50% of the population live in areas with these disease-transmitting mosquitoes, they are not just at risk of dengue, chikungunya and Zika – but any new arboviruses that emerge. There is lots of new and exciting research going on in this area, such as the development of novel vector control methods like <em>Wolbachia</em>, and outbreak early warning systems using climate data.</p> <p>Approaches that focus on the mosquitoes rather than the diseases themselves have the benefit of helping tackle all three of these diseases in one, as well as any emerging viruses that are spread by the same mosquitoes. Vaccines, diagnostics and antivirals will all have a role to play, but responses that are as broad and adaptable as possible could be hugely valuable – not just for the diseases that we know we need to control, but those that appear in the future.</p> </div> </div> </div> </div> </div> <p> <a target="_blank" rel="noopener noreferrer" href="https://www.gavi.org/vaccineswork/four-reasons-disease-carrying-mosquitoes-could-be-spreading-car-tyre-near-you">Original article</a> </p><p>This article was originally published on <a target="_blank" rel="noopener noreferrer" href="https://www.gavi.org/vaccineswork">VaccinesWork</a> </p><script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start': new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0], j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src= 'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f); })(window,document,'script','dataLayer','GTM-M7H54VD');</script><noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-M7H54VD" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript></article>

Mosquito. Credit: Jimmy Chan on Pexels

Earlier this month, the World Health Organization (WHO) gave a briefing on the rise of three mosquito-borne diseases: dengue, chikungunya and Zika. These viruses have been circulating for decades, but have historically presented a much lower health burden than a more familiar mosquito-borne threat – malaria. So why is the WHO worried about them now?

The incidence of dengue and chikungunya has grown dramatically in recent years. Just over 500,000 dengue cases were reported annually in 2000. By 2019, this had risen to 5.2 million. One in two people worldwide are now at risk of the disease.

Human behaviour has been enabling the expansion of these mosquito populations for centuries, via urbanisation, travel and trade. Allow these processes to occur at ever-increasing rates, throw climate change into the mix, and suddenly more than half the world’s population are living in areas at risk of mosquito-borne virus transmission.

Zika incidence has declined since a large outbreak in 2016, but experts are concerned that viral mutations and waning immunity could lead to outbreaks in the future.

The WHO is not just concerned about the increasing numbers of cases – we are also seeing outbreaks of mosquito-borne diseases in regions where cases have never been reported before. A handful of dengue and chikungunya cases have been reported periodically in Europe since 2010, but the WHO has warned that high numbers of cases in South America earlier in 2023 could be an indication of what is to come in Europe as summer gets underway.

These diseases are expanding into new regions with the mosquitoes that transmit them. By 2050 the yellow fever mosquito, which is responsible for the majority of dengue transmission, could reach as far north as Chicago and Shanghai. Another related species, the tiger mosquito, could live in large areas of France and Germany.

So what is driving this spread? It turns out that human behaviour has been enabling the expansion of these mosquito populations for centuries, via urbanisation, travel and trade. Allow these processes to occur at ever-increasing rates, throw climate change into the mix, and suddenly more than half the world's population are living in areas at risk of mosquito-borne virus transmission.

Urbanisation

The ancestors of the current yellow fever mosquito are thought to have lived in forests in sub-Saharan Africa. Their larvae grew in tree-holes and adults survived on the blood of non-human mammals. However, as humans moved into these habitats, the mosquitoes began to adapt. They started to lay their eggs on materials more commonly found in human environments, such as clay or rubber. They also evolved a preference for feeding on humans.

Today, the yellow fever mosquito thrives in urban and peri-urban areas, breeding in pools of water that has collected in anything from plant pots and water storage containers to tyres or uncollected rubbish. This means that rapid, unplanned urbanisation without the right infrastructure – like running water or waste collection – to accompany it creates the perfect breeding ground for these killers.

Have you read?

Globalisation

Dispersal across long distances was enabled by increased international trade. It is thought that the yellow fever mosquito spread to the Americas via ships soon after the Europeans first travelled there, likely via boats involved in the slave trade. The eggs are able to withstand desiccation for long periods of time, enabling mosquito eggs infected with arboviruses to survive the long journey across the Atlantic.

Nowadays trade in second-hand tyres has been associated with the spread of the yellow fever mosquito, as rain water that has collected inside the tyre can provide a welcoming environment for larvae to grow.

Nowadays trade in second-hand tyres has been associated with the spread of the yellow fever mosquito, as rain water that has collected inside the tyre can provide a welcoming environment for larvae to grow.

Human mobility

Movement of mosquitoes can lead to disease outbreaks in new areas, but so can the movement of people. According to the ECDC, cases of dengue are frequently reported in travellers returning from endemic countries, and these could lead to local spread in areas where mosquitoes are present.

Following the first ever dengue outbreak in Madeira in 2012, viral sequencing showed that the dengue virus detected there was closely related to viruses circulating in Venezuela at the time. Nearly 16,000 people travelled from Venezuela to Madeira by air in 2012.

Emergence of dengue in rural parts of Brazil has been associated with construction of roads connecting these areas to urban hotspots. A study carried out in Pakistan was able to combine climate data with mobile phone data to predict the outbreaks of dengue in new areas.

Climate change

The mosquitoes that transmit dengue, chikungunya and Zika are very sensitive to climate, and so predicting the impact of climatic changes on mosquito populations can sometimes be challenging. When it is warmer, mosquitoes can breed more quickly and the virus can replicate more quickly inside the mosquito, leading to faster transmission.

However, it's not as simple as 'higher temperatures means more mosquitoes'. If temperatures get too high, the standing water that these mosquitoes rely on to lay their eggs can dry out. This means other climatic factors such as rainfall patterns can also determine where mosquito populations are likely to flourish.

What can we do about it?

In 2022, the WHO set up the Global Arbovirus Initiative. At the launch event, Sylvie Briand, the WHO Director of Pandemic and Epidemic Diseases, said that "the next pandemic could very likely be due to a new arbovirus."

It’s not as simple as ‘higher temperatures means more mosquitoes’. If temperatures get too high, the standing water that these mosquitoes rely on to lay their eggs can dry out. This means other climatic factors such as rainfall patterns can also determine where mosquito populations are likely to flourish.

If 50% of the population live in areas with these disease-transmitting mosquitoes, they are not just at risk of dengue, chikungunya and Zika – but any new arboviruses that emerge. There is lots of new and exciting research going on in this area, such as the development of novel vector control methods like Wolbachia, and outbreak early warning systems using climate data.

Approaches that focus on the mosquitoes rather than the diseases themselves have the benefit of helping tackle all three of these diseases in one, as well as any emerging viruses that are spread by the same mosquitoes. Vaccines, diagnostics and antivirals will all have a role to play, but responses that are as broad and adaptable as possible could be hugely valuable – not just for the diseases that we know we need to control, but those that appear in the future.