Potential distribution of dominant malaria vector species in tropical region under climate change scenarios

Abstract

Risk assessment regarding the distribution of malaria vectors and environmental variables underpinning their distribution under changing climates is crucial towards malaria control and eradication. On this basis, we used Maximum Entropy (MaxEnt) Model to estimate the potential future distribution of major transmitters of malaria in Nigeria-Anopheles gambiae sensu lato and its siblings: Anopheles gambiae sensu stricto, and Anopheles arabiensis under low and high emissions scenarios. In the model, we used mosquito occurrence data sampled from 1900 to 2010 alongside land use and terrain variables, and bioclimatic variables for baseline climate 1960-1990 and future climates of 2050s (2041-2060) and 2070s (2061-2080) that follow RCP2.6 and RCP8.5 scenarios. The Anopheles gambiae species are projected to experience large shift in potential range and population with increased distribution density, higher under high emissions scenario (RCP8.5) and 2070s than low emission scenario (RCP2.6) and 2050s. Anopheles gambiae sensu stricto and Anopheles arabiensis are projected to have highest invasion with 47-70% and 10-14% percentage increase, respectively in Sahel and Sudan savannas within northern states in 2041-2080 under RCP8.5. Highest prevalence is predicted for Humid forest and Derived savanna in southern and North Central states in 2041-2080; 91-96% and 97-99% for Anopheles gambiae sensu stricto, and 67-71% and 72-75% for Anopheles arabiensis under RCP2.6 and RCP8.5, respectively. The higher magnitude of change in species prevalence predicted for the later part of the 21st century under high emission scenario, driven mainly by increasing and fluctuating temperature, alongside longer seasonal tropical rainfall accompanied by drier phases and inherent influence of rapid land use change, may lead to more significant increase in malaria burden when compared with other periods and scenarios during the century; especially in Humid forest, Derived savanna, Sahel and Sudan savannas.

Fig 1. Map of Nigeria with georeferenced sampling points of Anopheles gambiae species, showing topographic relief, ecological, regional and state boundaries.

Anopheles species sampling points reprinted for illustrative purposes only from Okorie et al. [48] under a CC BY 4.0 license, with permission from PLOS ONE [38].

Fig 2. Prevalence of An. gambiae species under low and high emissions scenarios and percentage change across all bioclimatic domains in Nigeria.

RCP2.6 represents low emissions scenario and RCP8.5 represents high emissions scenario.

Fig 3. Potential occurrence and distribution of An. gambiae s.l. in Nigeria.

(a) baseline climate 1960–1990, (b) low emissions scenario (RCP2.6) 2041–2060, (c) low emissions scenario (RCP2.6) 2061–2080, (d) high emissions scenario (RCP8.5) 2041–2060 and (e) high emissions scenario (RCP8.5) 2061–2080. Anopheles species sampling points reprinted for illustrative purposes only from Okorie et al. [48] under a CC BY 4.0 license, with permission from PLOS ONE [38].

Fig 4. Mean distribution density of An. gambiae species in each Nigerian state under baseline climates 1960–1990 and low emissions scenario (RCP2.6) / high emissions scenario (RCP8.5) in 2041–2060 (2050s) and 2061–2080 (2070s).

Note: red boundary line on the graph defines presence and absence conditions for each Anopheles species from zonal statistics; if 1 ≡ 0 (species does not occur), >1 = species occur, and 2 = maximum species prevalence [38].

Fig 5. Potential occurrence and distribution of An. gambiae s.s. in Nigeria.

(a) baseline climate 1960–1990, (b) low emissions scenario (RCP2.6) 2041–2060, (c) low emissions scenario (RCP2.6) 2061–2080, (d) high emissions scenario (RCP8.5) 2041–2060 and (e) high emissions scenario (RCP8.5) 2061–2080. Anopheles species sampling points reprinted for illustrative purposes only from Okorie et al. [48] under a CC BY 4.0 license, with permission from PLOS ONE [38].

Fig 6. Potential occurrence and distribution of An. arabiensis in Nigeria.

(a) baseline climate 1960–1990, (b) low emissions scenario (RCP2.6) 2041–2060, (c) low emissions scenario (RCP2.6) 2061–2080, (d) high emissions scenario (RCP8.5) 2041–2060 and (e) high emissions scenario (RCP8.5) 2061–2080. Anopheles species sampling points reprinted for illustrative purposes only from Okorie et al. [48] under a CC BY 4.0 license, with permission from PLOS ONE [38].