Many vector-borne diseases transmitted by flies would respond quickly to changes in weather and climate, because of the short lifecycles of several dipteran vectors, resulting in increasingly epidemic behavior of these diseases. Many vector-borne diseases are endemic to tropical and subtropical, but not temperate regions (3). However, according to the 2013 IPCC report, the expectations are that climate warming will occur earlier and be more severe toward the poles, as a result, temperate countries may be those most threatened by the emergence and re-emergence of vector-borne diseases. There are broadly three expected threats:
→ First, the risk from endemic vector-borne diseases might arise due to long-term changes in temperature and rainfall patterns.
→ Second, vector-borne diseases may shift their geographic ranges poleward (or to higher altitudes in mountains) toward regions where they did not exist before.
→ Third, climate change may increase the threat of the establishment of ‘exotic’ tropical/subtropical vector-borne diseases by increasing the climatic suitability of currently non-endemic countries, by increasing the abundance of vectors and pathogens in regions where they are currently endemic, and by increased frequency of introduction through increased international migration. Figure 3 represents these possible outcomes using impacts on one country.
Human Health, Vector-Borne Diseases, and Climate Change
Mosquitoes like (Aedes aegypti, Anopheles) serve as a vector that can carry various viruses and pathogenic bacteria, like dengue, yellow fever, Zika virus, Chikungunya, and most importantly the one disease that has been infecting humanity since ages “Malaria”. In 2019, there were an estimated 229 million cases of malaria worldwide. The WHO African Region carries a high share of the global malaria cases. In 2019, the region was home to 94% of malaria cases and deaths and unfortunately in 2019, 67% (274 000) Children aged under 5 years represented all malaria deaths worldwide.
Malaria is a life-threatening disease caused by parasites that are transmitted to people through the bites of infected female Anopheles mosquitoes. Anopheles mosquitoes thrive in regions with warm temperatures, humid conditions, and high rainfall. Therefore, tropical, and subtropical areas are ideal. Warm temperatures are also required for malaria parasites to complete their growth cycle within the mosquitoes. An increase in temperature, rainfall, and humidity may cause a proliferation of the malaria-carrying mosquitoes at higher altitudes, resulting in an increase in malaria transmission in areas in which it was not reported earlier. Malaria Scientific evidence suggests that malaria varies seasonally in highly endemic areas. Malaria is probably the vector-borne disease most sensitive to long-term climate change (27). The relationship between interannual climatic variation associated with the El Niño-Southern Oscillation (ENSO) cycle ( ENSO is a recurring climate pattern that involves changes in the temperature of waters in the central and eastern tropical Pacific Ocean…. El Niño and La Niña are the extreme phases of the ENSO cycle (see fig 3)) and malaria has been examined in various other countries.
For example, Venezuela experiences decreased rainfall during an El Niño year (see Figure 6.2). During the twentieth century, malaria rates regularly increased on average by over one-third in the year following an El Niño year. The possible reasons for this involve the combination of mosquito preferring high rainfall in the post-Niño year with temporarily reduced immunity levels in the local population following the previous lowincidence year (2). This is a matter of concern because the mosquitos are changing their geographical ranges, therefore other countries are expected to face an increase in malaria cases. There are some widely cited examples proposing that climate change has already resulted in the introduction of several infectious diseases into previously unaffected geographic areas. One such example is the spread of malaria into highland regions of East Africa, where this disease did not exist before. This spread occurred in an environment where the weather was much warmer and wetter than usual; it resulted in high rates of illness and death because the disease was introduced into a largely nonimmune population (1).
Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus. This mosquito also transmits chikungunya, yellow fever and Zika infection. Dengue is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature, and unplanned rapid urbanization. (See figure 6). Before 1970, only 9 countries had experienced severe dengue epidemics. The disease is now endemic in more than 100 countries in the WHO regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. The America, South-East Asia and Western Pacific regions are the most seriously affected. Cases across the Americas, South-East Asia and Western Pacific exceeded 1.2 million in 2008 and over 3.2 million in 2015 Climate change allows the primary dengue vectors to thrive in more geographical locations; increased population, urbanization and deforestation have also provided favorable conditions for vectors. The virus may be introduced to areas that previously were not at risk, and those, that are currently affected, may experience enormous increases in the number of cases. Endemic transmission in Africa and the Americas, recent outbreaks in Portugal, and the increasing incidence in Asia are proof of the challenges that plague an effective dengue control and the issues surrounding vector control (6).
The risk of dengue transmission has increased by warming climates, as the growth and development of mosquitoes are significantly influenced by temperature and humidity (4).
Climate affects weather, air and water quality, local and national food supplies, economics and many other critical health determinants. Observational evidence indicates that regional changes in climate, particularly temperature increases, affect a diverse set of physical and biological systems in many parts of the world.
References:
1-M.B. Hoshen , A.P.Morse ,”A weather driven model of malaria transmission”, Malaria Journal (2004): p.3:32
2-Patz, J. A., Githeko, A. K., McCarty, J. P., Hussein, S., Confalonieri, U., & De Wet, N. (2003). Climate change and infectious diseases. Climate change and human health: risks and responses, 6, 103-137.
3-Ogden NH. Climate change and vector-borne diseases of public health significance. FEMS Microbiol Lett 2017 Oct;364(19)
4- Bhatt S., Gething P.W., Brady O.J., Messina J.P., Farlow A.W., Moyes C.L., Drake J.M., Brownstein
J.S., Hoen A.G., Sankoh O. The global distribution and burden of dengue. Nature. 2013;496:504–507. doi: 10.1038/nature12060
5-Ollila, Antero. (2018). Challenging the scientific basis of the Paris climate agreement. International Journal of Climate Change Strategies and Management. 11. 10.1108/IJCCSM-05-2017-0107
6-Dash, A., Bhatia, R., Sunyoto, T., & Mourya, D. (2013). Emerging and Reemerging arboviral diseases in Southeast Asia. Journal of vector borne disease, 50(June 2013),
