By: Claire Slesinski, MSPH
Senior Program Manager for Global Urban Health

In 2015-2016, Latin America and the Caribbean experienced a dramatic outbreak of zika virus. This virus infected millions of people, many of them living in Brazil. The panic surrounding the zika virus outbreak was amplified by the fact that the virus was new to the region, and its impact on pregnant mothers and babies was especially devastating, resulting in lifelong effects.

The main culprit of this outbreak? The mosquito.

Mosquitos: The deadliest animal

Mosquito-borne diseases cause over one million deaths each year worldwide, making mosquitos the cause of more human suffering and death than any other animal or insect.

Mosquitos can spread malaria, chikungunya, dengue, yellow fever, several types of encephalitis, West Nile virus, and Zika virus to human beings. These diseases are spread by the Aedes aegypti mosquito, and in the case of malaria the Anopheles mosquito, which are found in tropical and sub-tropical regions, though their presence is expanding around the world.

Mosquitos thrive in warm cities

Mosquitos don't do well in areas where temperatures rarely rise above 65 degrees F. Below this temperature, they have a hard time flying, feeding, and breeding - activities necessary for their survival.

Urban environments located in warmer regions are ideal homes for mosquitos:

• Cities are home to large numbers of people and animals – the food supply for mosquitos.

• Cities tend to be warmer than surrounding suburban or rural areas, making them more comfortable places for mosquitos to live.

• Cities are covered in nooks and crannies where water can collect and mosquitos can lay their eggs – buckets, flowerpots, water storage containers, garbage and solid waste, plastic bottles and containers, puddles, and other structures found on and around homes and buildings.

Cities are getting warmer - and mosquitos are expanding their footprint

Increases in average temperatures are occurring worldwide due to climate change. With these increases in temperatures, many cities that were previously immune to infestation by the Aedes aegypti and Anopheles mosquitos may become victims to mosquito-borne diseases in the not-so-distant future.

For example, cities that sit at high elevation and have generally experienced cooler temperatures than the rest of the country, but they may eventually become warm enough for mosquitos to survive and breed there. Some cities previously believed to be safe from mosquitos, including Bogotá and Mexico City, are beginning to experience infestation by mosquitos that can carry dengue and other deadly diseases.

Complicating this is the fact that there is some evidence that within urban built environments, green areas where people might find some respite from high temperatures are at higher risk for  encouraging mosquito breeding and proliferation.

Additionally, populations living in informal settlements and urban slums, who already lack access to basic services such as piped water and sanitation systems, are more at risk of experiencing both the impacts of climate change related heat and weather events, and of contracting mosquito-borne diseases.

Dengue: A growing threat

Every year around the world, 100,000,000 cases of dengue cause severe infections with symptoms including fever, joint pain, and internal bleeding. Approximately 10,000 people die from dengue each year.

Latin America has experienced worsening dengue epidemics as temperatures have begun to increase during the past several years. The Pan American Health Organization (PAHO) received reports of more than 3,000,000 cases of dengue in 2019, exceeding the previous largest epidemic of dengue in the region in 2015 (2.4 million cases).

Source: Pan American Health Organization

Honduras, which also experiences high levels of inequality and instability, is responsible for more than 40% of dengue deaths that occurred in Central America in 2019. Reporting of cases for 2020 indicates that the dengue epidemic this year may be even worse than 2019.

Recently published research indicates that by 2080, 2.25 billion more people will be at risk of dengue than are currently at risk today, bringing the total population at risk of dengue to over 6.1 billion people by that year, representing 60% of the world’s future population.

Why is it so hard to control mosquito-transmitted diseases?

Controlling mosquito populations in cities can sound simple enough: eliminate standing water and containers where standing water might accumulate due to rainfall and cover any stored water that cannot be discarded.

Protecting human populations can be done using repellants and insecticides. Effective vaccines for most mosquito-borne diseases (except for yellow fever) do not yet exist.

Implementing these interventions is easier said than done.

Mosquito population control and personal protection from disease rely on the development of time consuming daily and weekly habits among members of entire communities, often involving making inconvenient choices that may be uncomfortable.

People living in areas vulnerable to mosquito-borne diseases are asked to wear long sleeves and long pants in hot weather, wear smelly mosquito repellant, spray the walls of their houses with insecticide, take malaria prevention medication that may have side effects, close up their houses with curtains and screens during hot weather, stay inside under bed nets before they’re ready to go to sleep, purchase special water containers and clean them on regular basis, get rid of potted plants that mosquitos might use for breeding, and cover other water containers that they might need or use for household activities.

These behaviors can be hard to accept for communities that don’t necessarily see mosquito-borne diseases as more deserving of their attention than other issues they are experiencing in their daily lives, especially among marginalized populations.

And even after adopting all these behaviors, mosquitos can still breed and community members may still become infected - mosquitos can lay eggs in any standing water or surface where water is likely to collect.

This is not even taking into account the financial burden of these prevention tactics – maintaining these behaviors over long periods of time is expensive for international organizations, governments, communities, and families.

Global action and recognition of mosquito-borne diseases

Of the diseases that can be spread by mosquitos, global long-term strategies have been developed for the prevention and control of malaria, dengue, and yellow fever. The World Health Organization (WHO) and its partners have created a Global Technical Strategy for Malaria (2016-2030), a Global Strategy for Dengue Prevention and Control (2012-2020), and a Global Strategy to Eliminate Yellow Fever Epidemics (2017-2026).

Though it’s currently unclear what the WHO’s strategy for Dengue will be beyond 2020, one small way you can note your support for Dengue control and prevention is to sign a petition for the creation of a World Dengue Day. The International Society for Neglected Tropical Diseases is hosting this petition, arguing that the creation of this global observance will help to “push for cohesive action and identify necessary healthcare solutions for the many millions affected by dengue.”

If established, World Dengue Day would join World Malaria Day (April 25) as the only other global observance related to mosquito-borne diseases acknowledged by the World Health Organization. 

You can find and sign the petition here.

As the world becomes warmer and mosquitoes can thrive in new places, global public health officials should turn their attention to these pesky bugs. They must be included as a part of a comprehensive global climate change adaptation strategy.