The El Niño: A Meteorological Risk Factor for Vector-borne Diseases
Updated: Aug 17
By Avi Patel, Stanton College Preparatory School, Jacksonville, Florida, USA
The El Niño Southern Oscillation (ENSO) has been ravaging numerous coastal and inland communities with excessive flooding and drought conditions, causing immense economic loss, and the incidence of many neglected tropical diseases. Affecting over 60 million people directly, El Niño remains one of the greatest enigmas to human health, and combined with the ever-escalating global climate crisis, El Niño events are only projected to increase in magnitude in the coming years (WHO, 2016).
The ENSO is a global climatic anomaly that alters global atmospheric circulation, thereby influencing temperature and precipitation levels throughout the world. The ENSO system consists of two acute phases: El Niño and La Niña. Spanish for “the boy” and “the girl,” El Niño and La Niña collectively alter the natural landscape of many developing nations in South America, Africa, and Asia. El Niño is usually associated with above-average ocean temperatures in the Eastern Pacific Ocean while La Niña is usually associated with below-average ocean temperatures in the Eastern Pacific Ocean (NOAA, n.d.). These systems induce flooding and drought-like conditions in different parts of the world depending on whether the year has been deemed as an El Niño year or a La Niña year. The figure below shows the disparity between flood damage between normal years and El Niño or La Niña years. Green regions represent areas with below-average rainfall and potential drought-like conditions. Meanwhile, red regions represent areas with above-average rainfall and potential flood-like conditions. ENSO cycles usually last between 3-7 years. El Niño phases are often followed by La Niña phases.
Figure 1. World map displaying anomaly in annual expected flood damage in El Niño (a) and La Niña (b) events (Ward et al., 2014).
Analyzing the red regions of this map is of particular global health importance due to the prevalent relationship between increased rainfall, and outbreaks of vector-borne infections.
Many theories have been proposed that link ENSO events and increased disease propagation. The most prominent theories state that when the Eastern Pacific Ocean experiences higher-than-average temperatures, higher rainfall is often experienced in the red regions shown in map (a). Many developing nations in this area do not often have adequate flood management infrastructure, and such excess water often contaminates drinking water systems (Ng et al., 2018). Warmer temperatures also promote bacteria proliferation, increasing susceptibility to waterborne infections. During the La Niña phase, the same phenomenon occurs in the red regions in map (b).
In addition to flooding, drought-like conditions have also been associated with increases in vector-borne diseases due to lower hygienic standards caused by a shortage of water (Ng et al., 2018). In this regard, ENSO can act as a double-edged sword. Both extremities in sea surface temperatures can increase vector-borne disease propagation in different ways.
The 2014-2016 El Niño event, one of the most studied because of its relative strength, has caused increases in vector-borne illnesses. For instance, cases of malaria, one of the most common vector-borne diseases around the world, have increased by 36.5% in Venezuela following the 2014-16 El Niño event (WHO, 2018). Additionally, cholera cases increased by roughly 50,000 in many East African countries (Benham, 2017). By the same token, La Niña has just as much potential in causing these outbreaks as El Niño, but in different regions and at different times.
The table from a Scientific Reports paper below provides a detailed portrayal of the different diseases transmitted along with the regions they affect.
Figure 2. Table of vector-borne diseases transmitted in the 2014-16 El Niño event, the countries it affected along with possible explanations for the transmission (Anyamba et al., 2019).
The relationship between ENSO events and disease transmission has been solidified through various studies. Yet, many experts comment that the escalating climate crisis will also play a significant part in strengthening future ENSO cycles. Historical trends already show a slight increase in El Niño trends since 1950, and with the added effects of climate change, such as sea-level rise, ocean temperature variations are predicted to be considerably altered (Wang et al., 2019).
As a result, the control of such illnesses remains an utmost priority as current infrastructure lapses lag significantly behind projected El Niño intensities. In order to ease the global disease burden, adequate urban planning including the development of efficient runoff systems and proper water storage facilities will need to be undertaken in ENSO vulnerable regions.
It is often easy to overlook the effects of the ENSO phenomenon in unaffected areas However, it is of critical importance that ENSO-induced vector-borne disease outbreaks are controlled in all impacted regions in order to prevent global transmission and large-scale epidemics.
Anyamba, A., Chretien, J.-P., Britch, S. C., Soebiyanto, R. P., Small, J. L., Jepsen, R., Forshey, B. M., Sanchez, J. L., Smith, R. D., Harris, R., Tucker, C. J., Karesh, W. B., & Linthicum, K. J. (2019). Global Disease Outbreaks Associated with the 2015–2016 El Niño Event. Scientific Reports, 9(1). https://doi.org/10.1038/s41598-018-38034-z
Benham, B. (2017, April 10). El Nino Shifts Geographic Distribution of Cholera Cases in Africa. Johns Hopkins Bloomberg School of Public Health. https://www.jhsph.edu/news/news-releases/2017/el-nino-shift-geographic-distribution-of-cholera-cases-in-africa.html.
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Ward, P. J., Jongman, B., Kummu, M., Dettinger, M. D., Sperna Weiland, F. C., & Winsemius, H. C. (2014). Strong influence of El Nino Southern Oscillation on flood risk around the world. Proceedings of the National Academy of Sciences, 111(44), 15659–15664. https://doi.org/10.1073/pnas.1409822111
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