How climate change influences pathogen transmission

Climate change is reshaping ecosystems worldwide and directly impacting human lives. Its consequences are more acutely felt in developing nations such as sub-Saharan Africa (SSA) and Southeast Asia. This commentary aims to highlight the specific challenges and potential mitigation strategies within the socioeconomic landscapes of these regions. It particularly examines the increased instances of vector-borne diseases like malaria, dengue fever, and chikungunya due to alterations in pathogen transmission [1].

Climate change is intricately associated with heightened transmission of vector-borne diseases, unfolding a multifaceted public health dilemma. Climatic alterations manifest through variations in weather patterns, ascensions in temperature, and deviations in precipitation, collectively creating environments that are favorable for the proliferation of vectors (Figure 1). Meanwhile, regions burdened with fragile health-care infrastructures and limited resources are facing escalating health disparities and burdens due to these climate-induced challenges.

Figure 1.

How climate changes influence pathogen transmission.

A recent study explored the effects of climate change on transmission and susceptibility of populations to mosquito-borne diseases across varying altitudes and population densities, employing a comprehensive multi-model, multi-scenario framework [2]. The authors projected alterations in transmission season lengths and global population susceptibility, from 1951 to 1999 for malaria and dengue, utilizing projections derived from six distinct mosquito-borne disease models, orchestrated by four global circulation models. Notably, the findings revealed a significant expansion in climate-suitable conditions for malaria and dengue transmission, particularly among regions already afflicted by these diseases. Malaria suitability extended by additional 1.6 months in tropical highlands across Africa, the Eastern Mediterranean region, and North and South America. Concurrently, dengue suitability increased in the lowlands of the Western Pacific and Eastern Mediterranean regions by additional four months. Contrary to expectations, rural areas exhibited higher susceptibility amplification compared to urban ones, leading to an extension of the epidemic belt toward temperate regions and potentially placing up to 4.7 billion more individuals at risk by 2070 relative to 1970–99, particularly in lowlands and urban locales. Extrapolating these findings unveils a grim potential reality of disease outbreaks in regions lacking immunological resilience, and public health infrastructures unprepared for epidemiological challenges [1].

Excessive rainfall or severe droughts serve as a double-edged sword in vector-borne disease transmission. While abundant rainfall generates optimal breeding sites for vectors, thus elevating the risk of disease outbreaks, drought conditions concentrate vectors around the remaining water sources, escalating the risk of transmission of diseases such as plague. However, in the case of Yersinia pestis, the causative agent of plague, drought conditions may actually contribute to a reduction in the prevalence of the disease by limiting the population of flea vectors or their mammalian hosts, as per some studies.

Moreover, the emergence of unpredictable and severe weather events disrupts established vector control strategies and public health initiatives, impairing their effectiveness and complicating containment and response efforts. This often results in the resurgence of diseases like malaria in regions where they were previously controlled or eradicated. Altered climatic conditions are also extending the transmission seasons of vector-borne diseases, sustaining elevated transmission rates over extended periods.

Outside of its direct impact on vector-borne disease dynamics, climate change has other subtle yet equally significant consequences that must be considered [3,4]. For example, temperature fluctuations can modify the biting behavior of vectors. As temperatures rise, some mosquito species might bite more frequently, thereby elevating the risk of disease transmission. Climate-induced shifts in animal and bird migration patterns can considerably alter their feeding preferences, which in turn affects human biting incidence rates. Variations in migration routes or timing might pave the way for unexpected outbreaks by introducing new reservoirs of diseases or vectors into regions, resulting in unforeseen epidemics. Human displacement caused by climate factors, such as rising sea levels, droughts, or resource scarcities, can also influence vector distribution. Migrating populations might inadvertently introduce vector-borne diseases to new areas because of climate change, or they might be more susceptible due to a lack of immunity or prior exposure. These dynamics underscore the need for a holistic understanding of how climate change redefines the vector-borne disease landscape.

Determining the exact influence of climate change on these diseases is challenging, given the interplay with other variables such as urbanization, deforestation, and human mobility, which complicate the intricate relationships between climatic variables and disease transmission dynamics. Thus, observational studies and scenario-based modeling are pivotal in unraveling the subtle connections between climate change and vector-borne diseases, and in forecasting how future climatic conditions might alter the distribution, abundance, and transmission seasons of vectors. Deliberate analysis substantiates these concerns. An analysis over time of monthly occurrences of malaria in the highlands of Colombia and Ethiopia during warmer years indicates a transition in its presence to higher altitudes. Without suitable control measures, the prevalence of malaria is projected to escalate at elevated terrains due to global warming [5]. [1] From 2007, there has been a near 40% decrease in the global disability-adjusted life years (DALYs) rate related to malaria; nonetheless, the predominant impact is still felt in Africa, which accounts for over 90% of all deaths due to malaria [6]. Aedes aegypti, the primary carrier of arboviral diseases such as dengue, chikungunya, yellow fever, and Zika virus, has experienced global proliferation, threatening almost half of the world’s population [7]. This spread is in part related to the rise in global temperatures, as occurrences of dengue have a positive correlation with weather conditions, including temperature, precipitation, and relative humidity [1].

Chikungunya virus, first discovered in Tanzania, initially caused localized outbreaks in Africa and Asia, mainly in countries bordering the Indian Ocean [1]. The continuous spread of the virus is facilitated by travel and trade, with projections indicating potential expansions of transmission-suitable areas in China, South Asia, and Southern Africa due to unfavorable climatic conditions.

Climate variability significantly influences the transmission of schistosomiasis in sub-Saharan Africa (SSA), affecting the production, survival, and reproductive rates of freshwater snails, the hosts for schistosomes [8]. The impacts of climate variability, such as altered precipitation patterns and temperature fluctuations, can lead to increased flooding events or changes in water bodies, creating favorable conditions for snail proliferation and, consequently, schistosomiasis transmission [8].

Regions such as Southeast Asia and sub-Saharan Africa (SSA) face heightened risks due to socio-economic disparities, limited healthcare access, and inadequate sanitation facilities, exacerbated by climate change impacts on infectious diseases. Adaptive, integrated strategies are imperative to efficiently counteract these impacts. These strategies include enhanced surveillance, fortified health-care systems, active community engagement, and climate-resilient interventions, all tailored to regional specifics and socio-economic contexts. A collaborative approach involving governments, international organizations, local communities, and the private sector is essential to navigate the intricate impacts of climate change, such as disease transmission. Key elements in developing resilient solutions include elevating educational outreach, enhancing healthcare access, and fostering environmental sustainability.

To effectively mitigating the impacts of climate change on vector-borne diseases, there is a necessity for the deployment of diverse strategies, such as advanced early warning systems to facilitate timely interventions and avert potential outbreaks, and investing in the development of innovative vaccines, treatments, and stringent vector control measures. Nonetheless, the complex interplay between climate change, poverty, inequality, and conflict complicates addressing these diseases, collectively exacerbating vulnerabilities and compounding public health efforts. An integrated and comprehensive approach is crucial to resolve socio-economic disparities, environmental alterations, and health challenges, considering the multifactorial nature of these challenges. In conclusion, managing and mitigating the diverse and interconnected problems precipitated by climate change in regions like SSA and Southeast Asia requires a united, comprehensive approach, ensuring the well-being and prosperity of their populations amidst escalating environmental challenges.

Funding Statement

The author(s) reported that there is no funding associated with the work featured in this article.

Disclosure statement

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Author contributions

AZA developed the study design, performed data extraction, manuscript drafting and reviewing