Climate impacts spur alarming spread of vector-borne diseases
Dengue fever is mainly spread by the bite of infected Aedes mosquitoes, which includes A. aegypti and A. albopictus mosquitoes.
What you need to know:
- The recent report by WHO brings attention to the Aedes mosquito, predominantly the Aedes aegypti species, as the principal carrier of dengue.
- This mosquito's adaptability to flooded and arid environments has fuelled a concerning increase in dengue cases, ranging from 100 to an estimated 400 million annually.
The World Health Organization (WHO) has escalated a global concern regarding the impact of climate change on public health. The organisation emphasises the increasing incidence and geographical expansion of disease-causing pathogens, significantly driven by shifting climate patterns. Climate change manifests through prolonged temperature variations, intensified tropical storms, and rising sea levels, creating conducive environments for the proliferation of viral illnesses.
Raman Velayudhan, the head of WHO's Global Programme on Control of Neglected Tropical Diseases, highlighted the alarming surge in dengue prevalence, which has risen eight-fold since 2000. Approximately 129 countries, encompassing nearly half of the global population, now face a significant risk of dengue transmission.
The recent report by WHO brings attention to the Aedes mosquito, predominantly the Aedes aegypti species, as the principal carrier of dengue. This mosquito's adaptability to flooded and arid environments has fuelled a concerning increase in dengue cases, ranging from 100 to an estimated 400 million annually.
WHO Director-General Tedros Adhanom Ghebreyesus urged nations to proactively equip themselves to manage the dengue transmission surge and other arboviruses. This urgency is grounded in the impending El Niño event predicted for 2023 and 2024, a sentiment echoed by the World Meteorological Department. The agency anticipates Kenya to bear the brunt of El Niño's impact, leading to an elevated spread of diseases like malaria and dengue fever, coupled with flooding, flash floods and landslides during the September-October rainfall period.
On a localised scale, the Kenya Meteorological Department foresees heightened precipitation and flood risks due to the impending El Niño phenomenon. This event is poised to impact regions including southern South America, the southern United States, the Horn of Africa and Central Asia. Dr David Gikungu, director of the Kenya Meteorological Department, underscored the historical correlation between El Niño and intense rainfall and flooding, particularly affecting East Africa.
Coastal waters, warmed by global climate change, have exacerbated the proliferation of disease-causing agents and their vectors. Bacteria, viruses and protozoa originating from sewage and industrial wastewater provide fertile breeding grounds for vectors such as the Aedes aegypti mosquito. These contaminants infiltrate oceans through sewage overflows and polluted stormwater runoff, further exacerbating waterborne diseases like dengue transmission dynamics.
Dengue fever, characterised by symptoms ranging from mild flu-like manifestations to severe conditions like dengue hemorrhagic fever and dengue shock syndrome, has increased prevalence due to urbanisation, inadequate mosquito control, and global population movement. The Aedes mosquito, with its daytime biting behaviour, has expedited transmission rates.
Urban expansion and population concentration provide breeding opportunities for mosquitoes, while climate change expands Aedes mosquitoes' geographical range. Human travel introduces the virus to new regions, underscoring the necessity of effective sanitation measures and mosquito population control to curb disease propagation.
Regrettably, specific antiviral drugs targeting dengue are not yet available. Treatment primarily focuses on alleviating fever and pain. There are four known serotypes of dengue virus—DENV-1, 2, 3, and 4—with co-circulation of all four becoming a common feature in most tropical countries in recent years. In regions like Kenya, dengue, alongside malaria and chikungunya, poses significant health risks, especially among children, with outbreaks more prevalent during wet seasons.
The prevalence of dengue fever illustrates a significant increase in the proliferation of climate change-linked zoonotic diseases – those naturally transferred between animals and humans. In East Africa, where a wealth of freely roaming wild animals, the seasonal movement of livestock, and diverse interactions between animals and humans occur at multiple junctions, all set against a tropical backdrop, the region provides conducive circumstances for the heightened transmission risks of various zoonotic diseases.
Beyond dengue, the broader implications of climate change on human health encompass a spectrum of health complications. Elevated temperatures and increased ground-level ozone exacerbate respiratory issues, triggering asthma attacks and worsening chronic respiratory ailments.
Shifts in climate lengthen pollen seasons, intensifying allergic reactions and asthma. Escalating heat-related illnesses, particularly among vulnerable populations, and alterations in precipitation patterns contributing to waterborne diseases and freshwater source contamination, further compound health challenges.
Mental health too, is affected, with extreme weather events inducing psychological distress and anxiety due to displacement and livelihood loss. Climate change indirectly influences disease patterns through vectors like mosquitoes, potentially compromising immunity and heightening cortisol levels due to stress from extreme weather, thereby disrupting health and immune functions.
