Explainer

How climate change affects vector-borne diseases

As climate change alters temperatures and weather patterns around the world, the risk of vector-borne diseases like dengue fever and Zika virus will increase. Here’s what that means for global health and what can be done to limit the damage.

Man spraying insecticide in garden to prevent adult mosquitoes spreading dengue virus
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How climate change affects vector-borne diseases
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What causes vector-borne diseases? 

A vector is a living organism – like a tick or mosquito – that transmits an infectious agent from an infected animal to a human or another animal.

How is climate change increasing the risk of vector-borne diseases? 

Virtually all vector-borne diseases have a climate dimension. There are three key ways climate change affects vectors: 

  1. More places will become suitable for vectors. Warmer temperatures can increase the geographic spread of where vectors – like mosquitoes and ticks – can survive and breed. Increased rainfall can increase the amount of standing water, creating more breeding areas for many vectors. Droughts can also support breeding by forming pools of standing water from previously flowing water. 
  2. Warmer climates extend the disease transmission season. Climate change is improving the climatic and environmental conditions for the transmission of many diseases. This may also lead to an increase in the duration of disease transmission seasons. 
  3. Temperature change can affect the behaviour of vectors. For example, increased temperatures change the biting behaviour of mosquitoes, reducing the effectiveness of barriers such as bed nets.  

What are the risks? 

According to a 2019 study in the journal PLOS Neglected Tropical Diseases, by 2050, disease-carrying mosquitoes will ultimately reach 500 million more people than they do today.

One vector – the Aedes mosquito – is responsible for the spread of some of the most concerning escalating infectious diseases such as Zika, chikungunya, West Nile virus and dengue fever.

Man releasing a tube of mosquitoes that carry Wolbachia from his car window

Marcos has been working with the World Mosquito Program in Niteroi for a year, releasing mosquitoes that carry Wolbachia bacteria. It’s the first day of a second round of releases. His car contains 900 tubes, which are released every 50 metres.

Mosquitoes carrying Wolbachia are less able to transmit dengue, and, over time, the Wolbachia mosquitoes breed with the wild mosquito population, leading to a decrease in the spread of infection. 

Credit:

Adrienne Surprenant / Collectif Item, Wellcome

Licence: All Rights Reserved

Dengue is a mosquito-borne viral infection that causes a flu-like illness and in severe cases can cause hospitalisation and possible death. It is typically found in tropical and sub-tropical climates but has expanded globally since 1990, particularly in Latin America and the Caribbean, South Asia, and sub-Saharan Africa.

According to a Intergovernmental Panel on Climate Change 2022 report, “dengue risk will increase with longer seasons and a wider geographic distribution in Asia, Europe, Central and South America and sub-Saharan Africa, potentially putting additional billions of people at risk by the end of the century." 

However, while some areas are warming to suitable conditions for vectors to thrive, others will become too hot for them to survive.

Laboratory experiments found that Aedes aegypti (a species of mosquito) larvae die when the water temperature surpasses 34°C, and the adults start to die when the air temperature is above 40°C. To survive, mosquitoes have been discovered shielding in small-scaled environments – like cement tanks, tires or household pitchers – where ambient temperature change does not prevail.  

Mosquitoes are not the only concerning vector.  

Ticks are another vector capable of transmitting many pathogens, including serious zoonotic viruses. Tick expansion is promoted by the warmer winters in the last decade due to global warming.

Ticks that carry the virus that causes tick-borne encephalitis have moved into northern subarctic regions of Asia and Europe. In 2019, tropical disease-carrying ticks were also found to have survived in Germany through the winter months. This discovery could indicate that these ticks are moving towards establishing themselves in new northern territories.

What can be done to reduce the risk? 

Climate change is increasing the risk of vector-borne diseases. The sooner we act to mitigate the impacts of climate change – by transitioning from using fossil fuels to clean, renewable energy – the better off we’ll be in the future. 

But mitigation alone will not be enough. There are other actions we must take to adapt to the risks: 

  • provide universal access to care and disease management 
  • improve disease surveillance, including health education and community surveillance for early outbreak detection 
  • minimise vector exposure (for example, by using window and door screens, protective clothing, insecticide or habitat avoidance) 
  • accelerate vaccine development with new technologies 
  • prioritise wetland management and elimination of vector breeding sites in the vicinity of populations 
  • investigate novel vector control methods (for example, the Wolbachia-infected mosquitoes

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