Impact of ENSO 2016–17 on regional climate and malaria vector dynamics in Tanzania

Abstract

Large scale modes of climate variability, including the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), have been shown to significantly impact mosquito-borne diseases in the Tropics, including malaria. However, the mechanistic cascade from ENSO and the IOD, to induced changes in regional climate and ultimately mosquito abundance and behaviour is poorly understood. Mosquito population dynamics, behaviour and their potential to transmit disease are all sensitive to micro-climatic conditions. The warm phase of ENSO (El Niño) tends to be associated with increased precipitation and outbreaks of various vector-borne diseases, while the cold phase (La Niña) can cause drought during the short rains over East Africa. The sensitivity of Anopheles mosquito population dynamics and host-seeking behaviour to ENSO and to the resulting micro-climatic conditions, were investigated in the Kilombero Valley in Tanzania. From June 2016 to September 2017, changes in the timing and intensity of the rainy seasons and temperature due to the ENSO 2016-17 were observed. Mosquitoes were collected using Centres for Disease Control and Prevention (CDC) light traps indoors and mosquito electrocuting traps in-and outdoors. Changes in abundance and biting behaviour of Anopheles arabiensis and Anopheles funestus were correlated with climate and microclimate. The impacts of El Niño on climate and mosquito abundance were not clear. However, the study area experienced a drought due to La Niña during which both vector species declined significantly. An. arabiensis densities stayed more stable at higher temperatures and were found in higher numbers outdoors with respect to An. funestus. For both species, indoor temperature and season determined their host-seeking location, with higher temperatures and the wet season driving them outside. The study confirmed the influence of ENSO and micro-climate on malaria vector abundance and host-seeking behaviour, generating hypotheses for predicting the impact of future ENSO on malaria risk and vector control. Our observation of higher outdoor biting during warmer conditions indicates that indoor vector control strategies may become proportionally less effective during this time.

Spatio‐temporal patterns of malaria incidence in Rwanda

“…For instance in Uganda, climatic changes contributed to a favourable environment for malaria transmission, and had a detrimental effect on malaria reduction gains achieved through intervention scale‐up efforts during the previous 5 years (Ssempiira et al, 2018). Although the El Niño effect could not be established, the following La Niña episode caused drought at a regional scale which led to the significant decrease in malaria vectors (Kreppel et al, 2019). Apart from climate variability, additional factors of increased malaria incidence are increasing population density and internal migrations (National Institute of Statistics of Rwanda, 2012a); irrigated surfaces and rice paddies (Nabahungu & Visser, 2013) interacted with local climate variability and change (Henninger, 2013b) to create a conducive environment for the Anopheles mosquito.…”

Interannual Climate Variability and Malaria in Mozambique

“…3 of 17 studies yielded mixed results. However, recent efforts have increasingly shifted to examining the interactions between ENSO, along with other modes of interannual climate variability, and their influences on rates of malaria (e.g., Behera et al, 2018;Bouma & van der Kaay, 1996;Diouf et al, 2020;Ikeda et al, 2017;Kreppel et al, 2019;Landman et al, 2020;J. Smith et al, 2017a).…”

“…However, recent efforts have increasingly shifted to examining the interactions between ENSO, along with other modes of interannual climate variability, and their influences on rates of malaria (e.g., Ikeda et al, 2017;Behera et al, 2018;J. Smith et al, 2017;Kreppel et al, 2019;Bouma and van der Kaay, 1996;Diouf et al, 2020;Landman et al, 2020). In particular, the major tropical ocean basin on the eastern side of Africa, the Indian Ocean, holds considerable potential for predictability at the interannual time scale (e.g., Webster et al, 1999;Behera and Yamagata, 2001).…”

“…Of these, only six studies investigated potential linkages between the El Niño‐Southern Oscillation (ENSO) and malaria epidemics in Africa, and those studies yielded mixed results. However, recent efforts have increasingly shifted to examining the interactions between ENSO, along with other modes of interannual climate variability, and their influences on rates of malaria (e.g., Behera et al., 2018; Bouma & van der Kaay, 1996; Diouf et al., 2020; Ikeda et al., 2017; Kreppel et al., 2019; Landman et al., 2020; J. Smith et al., 2017a). In particular, the major tropical ocean basin on the eastern side of Africa, the Indian Ocean, holds considerable potential for predictability at the interannual time scale (e.g., Behera & Yamagata, 2001; Webster et al., 1999).…”

Information Entropy as Quantifier of Potential Predictability in the Tropical Indo-Pacific Basin

“…They impact key variables of societal relevance, from surface temperature to precipitation and the frequency of extreme events such as tropical cyclones, typhoons and droughts. These climate modes are of the uttermost importance not only for water and food security, but also for global health, as they modulate, for example, malaria occurrences in India (Dhiman and Sarkar, 2017;Anyamba et al, 2019), Indonesia (Kovats, 2000) and Africa (Hashizume et al, 2012;Kreppel et al, 2019). Assessing their potential predictability and quantifying how this predictability is simulated in climate models and projected to change in the future, is a priority.…”