Evan Heffelfinger

When you think of “climate change” you probably think of how hot it gets in Pittsburgh during the summer, how we barely get snow anymore, or perhaps that winter a couple of years ago when we had seventy-degree days once a week. While I certainly welcomed being able to wear shorts and hang out with my friends on the Cathy lawn in January, it was concerning. However, climate change is a real issue that impacts multiple facets of life, not just here, but all across the globe. One of the most dangerous impacts of our rapidly heating world is the spread of diseases to new places. Namely, vector-borne diseases, such as malaria, dengue fever, and chikungunya. Which  are all illnesses spread by mosquitoes that prefer these increasingly hot and humid environments to breathe and thrive.

Vectors, Diseases, and Why They Are Spreading

With increasing temperatures and more prevalence of diseases, neglected tropical diseases such as malaria, dengue fever, and chikungunya are now on the rise. Recently, neglected tropical diseases have spread farther north in North America and Europe and to higher altitudes in mountainous regions. European nations, specifically, have long seen themselves as immune to neglected tropical diseases, as the climate in this region simply was not supportive of mosquitoes. However, the migration patterns of mosquitoes have changed in recent years, seeing species move farther north on the European continent. The Asian tiger mosquito, Aedes albopictus, is of particular concern in the European region. This mosquito, known to carry chikungunya and dengue viruses, has been able to survive and reproduce in high quantities in higher latitudes. This has led to established populations being reported in southern Europe over the last decade and even isolated populations as far north as the United Kingdom. 

Additionally, mosquito species that have previously been prevalent in Europe one hundred years ago and disappeared have returned. Aedes aegypti, which is responsible for spreading yellow fever, dengue, chikungunya, and Zika, has been reported in Europe as recently as 2022. A. aegypti is more concerning than A. albopictus, not only because it is more efficient at transmitting viruses, but it is also associated more closely with human populations, increasing opportunities for transmission. In 2022 alone, locally reported cases of dengue in mainland Europe were equal to the number reported between 2010 and 2021. 

Even mosquito species native to Europe have seen increasing populations and rapidly increasing transmission. Culex mosquitoes, which are native to the European continent and spread West Nile Virus, have seen population growth. This is complemented by increasing case counts of West Nile Virus in the past decade on the continent, with cases being reported at higher latitudes than expected. This growth is not unprecedented, as New York City famously had an outbreak of West Nile Virus in 1999, marking the first time that an “old world” virus had been identified in the Eastern Hemisphere. 

Climate change leads to greater and more expansive populations of disease-carrying mosquitoes because of two factors: rain and heat. Mosquitoes thrive in warm and humid conditions, laying their eggs in standing water. Even the tiniest amount of standing water, like a bucket in a backyard garden, is a sufficient breeding ground for mosquitoes. Therefore, as regions at higher latitudes face hotter and wetter summers, they also foster greater opportunities for mosquitoes to thrive and reproduce.

Furthermore, recent concerns have voiced that vectors may have genetically different responses  due to climate change and therefore, selective pressures  can evolve to possess an increased ability to transmit disease.

Effects of Increased Disease Burden

These viruses are legitimate public health threats, especially in regions where much of the population may be immunologically naïve, meaning that they have not been exposed to the disease and, therefore, do not have any immunity. malaria, West Nile Virus, dengue fever, and chikungunya tend to be mild but can cause severe complications and death in elderly or immunocompromised patients. One of the more concerning impacts in Europe is that these diseases may be transmitted through organ and blood donations. Even more alarming is the fact that there may be shortages of blood and organs due to an outbreak of a neglected tropical disease.

What Can Be Done?

The most obvious solution to this problem of the ever-expanding mosquito habitat is to simply “fight climate change.” Well, this is already being done through environmental regulations and greater awareness of carbon footprints. Not to say that this is not a good thing, but more specific efforts need to be taken to combat neglected tropical diseases existing in places that are anything but tropical.

The surveillance of mosquito populations is one of the most impactful tools to combatting this crisis. However, adequate surveillance of mosquitoes is extremely labor-intensive and is not often achievable by health authorities alone. Scientists in Barcelona, Spain have established a project called Mosquito Alert, which allows people to photograph mosquitoes and report them through an app. This system updates mosquito counts in real time and maps the locations of populations. In 2018, an app user documented the first sighting of Aedes japonicus outside of central Europe. Spanish health authorities said they would have never considered sampling for A. japonicus had it not been for this documentation. Co-founder John Palmer hopes that Mosquito Alert can be expanded globally, especially to regions where neglected tropical diseases are endemic and have significant disease burdens.

In Europe, vaccines are approved for malaria, dengue, and chikungunya. However, despite the efforts of the European Union, vaccine inequities exist. This is not an issue exclusive to neglected tropical diseases, nor the European continent. Although this inequality is not unique to Europe, these inequities have a negative impact on the combat against neglected tropical diseases. Vaccine access inequities are best combated at community and local levels, so raising awareness about the threat of neglected tropical disease outbreaks will help these community organizations combat these threats.

The alarming reality of neglected tropical diseases in Europe is that they can be transmitted locally. This was not always the case, as these diseases used to be acquired almost exclusively because of international travel. One major implication of this reality is the increased threat of an outbreak of a disease such as malaria or dengue. Hospitals in northern Europe are not entirely equipped to handle outbreaks of this nature. Malaria, for example, can require IV antimalarial therapy if a patient is unable to take oral medication. In a large-scale outbreak, this resource may become scarce. This can be combated by increasing the capacity and stock of these medications, primarily by ensuring that supply chain volumes can be increased in this scenario. 

Heightened awareness of the very real threat posed by tropical diseases in non-tropical climates. While the threat is imminent, there is still much that can be done to combat this threat and ensure that human populations are safe. Humans cannot directly reverse the altered migration patterns of mosquitos, but steps can be taken to indirectly return the climate to historically normal patterns and to prepare for oncoming public health threats.