Navigating the intersection of climate crisis and mosquito-borne menace
By: Maya Ardon
The world’s deadliest animal is not a snake, a shark, or a lion – it’s neither a ferocious mammal you have to fight or a formidable underwater creature like those found in the pages of fantasy novels. Rather, mosquitoes kill more people every year than any other animal in the world. Mosquitoes are often thought of as nuisance insects that leave itchy rashes in wake of their bites, but they transmit deadly diseases, cause lifelong disabilities in survivors, and contribute to major concerns in global environmental health. They are the most important arthropod disease vectors globally; more than one million people are killed and an estimated 700 million people are infected each year from mosquito-borne diseases.
Most mosquito-borne diseases occur in tropical and subtropical climates. However, many of these diseases are spreading as warmer temperatures increase habitat suitability for mosquitos and allow them to propagate into new geographical areas. Notably, it is difficult to isolate the role of climate change in the increase of infectious disease transmission, as other non-climate factors also affect the presence of a disease and its distribution in an area. This includes globalization, land-use changes, sociodemographic factors, differences in public health systems, and characteristics of the vector or disease itself. In addition to global trends influenced by climate change, local weather pathways such as rainfall, humidity, and temperature play an important role in the viability and efficacy of mosquitoes as vectors. These factors have been shown to increase the incidence of dengue fever and malaria and their effect is projected to grow, extending beyond endemic areas towards higher altitudes and temperate climates.
The expansion of these severe diseases is likely to result in outbreaks occurring where people may be “immunologically naive and public health systems unprepared.” Many diseases that are spread by mosquitoes comprise a wider group of neglected tropical diseases (NTDs); as the climate in parts of the world becomes warmer and wetter, these diseases are poised to spell trouble for the non-tropical countries that have historically ignored them. The effects of these diseases are thus limited not only to places where risk of infection has historically been higher, but also to new countries where mosquito-borne diseases have not posed a significant public health risk before. Outbreaks of disease in Europe and North America have tended to result from travelers returning with the disease from abroad. However, it is possible that dengue – which had previously disappeared from Europe when Aedes aegypti mosquitoes disappeared – may re-establish itself, spreading northward from Southern Europe.
The future of these diseases depends on the further development and improvement of vaccines, vector control methods, and the ability to implement them internationally. It is a multifaceted challenge, as eradication and vaccination programs are underlined by inequity in the way they are distributed. For example, the first vaccine against chikungunya was recently approved by the United States Food and Drug Administration, seen as an “important advancement in the prevention of a potentially debilitating disease with limited treatment options.” The risk of infection is highest in places with large populations of two mosquito species: Aedes aegypti and A. albopictus; these places include (sub)tropical regions of Africa, Southeast Asia, and parts of the Americas where the disease-carrying mosquitoes are endemic. However, the vaccine is likely to reach travelers from the US, military members, and researchers traveling to affected areas rather than locals faced with greater exposure. Beyond availability, affordability is a concern underlying the accessibility of the vaccine in low- and middle-income countries that experience chikungunya outbreaks. Many initiatives and organizations are pushing to invest in and ensure that prevention and protection against mosquito-borne diseases – including, but not limited to chikungunya – can be actualized universally. The nonprofit Coalition for Epidemic Preparedness Innovations (CEPI) has helped foster partnership between Brazil’s Butantan Institute and Valneva to develop affordable commercialization of the vaccine in Brazil and other low- and middle-income countries.
Disease transmission remains an important facet of global health, and overlaps with many other issues, including but not limited to health equity, resilience of diseases and vectors to biological and integrated control measures, and changing human geographies. As the climate crisis continues to unfold, it is crucial not to overlook all of these concerns. While progress has been made in treating and preventing certain diseases, recognizing infectious diseases as integral to the climate crisis is essential to effectively combat global disease transmission and enhance environmental health worldwide.