Variation in species composition and infection rates of Anopheles mosquitoes at different altitudinal transects, and the risk of malaria in the highland of Dirashe Woreda, south Ethiopia

Abstract

BackgroundThe transmission of malaria is heterogeneous, and varies due to altitude. The information on whether the transmission of malaria is indigenous or imported to highland areas is scarce. Therefore, this study aimed to assess the species composition and infection rates of Anopheles at different altitudinal transects, and the risk of malaria if any in the highland of Dirashe Woreda, South Ethiopia.MethodsThis study was conducted in Gato (low altitude; average elevation of 1273 m), Onota (mid-altitude; average elevation of 1707 m) and Layignaw-Arguba (high altitude; average elevation of 2337 m) from August 2015 to April 2016. Anopheles mosquitoes were sampled using Centers for Disease Control and Prevention (CDC) light traps from thirty houses (ten houses from each village). The circum-sporozoite proteins (CSPs) rate and entomological inoculation rate (EIR) of Anopheles mosquitoes were estimated. For the epidemiological survey, malaria cases were collected from laboratory registration books of selected health facilities from (August 2015-April 2016). A cross-sectional survey was done to collect data on malaria vector control activities in each village (August-September 2015).ResultsOne thousand two hundred sixty-eight Anopheles mosquitoes comprising Anopheles arabiensis, An. demeilloni, An. cinereus, An. pharoensis, An. funestus-group, An. pretoriensis, An. christyi, An. ardensis and An. tenebrosus were identified in the study area. Anopheles arabiensis was the dominant species in Gato, whereas An. demeilloni was the dominant species in Layignaw-Arguba. Five mosquitoes, three An. arabiensis from Gato and two An. demeilloni from Layignaw-Arguba, were positive for Plasmodium falciparum CSPs. Plasmodium falciparum CSP rate was 0.4% (95% CI: 0.08–1.15) for An. arabiensis in Gato, and it was 0.64% (95% CI: 0.08–2.3) for An. demeilloni from Layignaw-Arguba. The P. falciparum EIR of An. arabiensis was 8.6 (95% CI: 2.4–33.4) infectious bites/person/nine-months in Gato. Plasmodium falciparum parasite was dominant in Gato (88%) and Onota (57.5%), whereas in Layignaw-Arguba P. vivax (59.4%) occurred most frequently. Increased malaria cases were observed in children age 5–14 years in Gato (P < 0.05), whereas in Onota and Layignaw-Arguba there was no statistically significant difference in malaria cases among the age groups. Households owning at least one long lasting insecticidal net were 92.7% in the study area, and 77.6% slept under the net during the preceding night of the survey. About 64.4% of the households in Gato were protected by the indoor residual spray. However, the spraying was done when the density of local malaria vectors was low.ConclusionIncrimination of Plasmodium CSP positive Anopheles species and the presence of malaria in children under five years in high altitude Layignaw-Arguba may justify the existence of indigenous malaria transmission and the need for effective malaria control. Further investigation and confirmation using more sensitive molecular techniques are however needed to consider An. dem...

Use of epidemiological and entomological tools in the control and elimination of malaria in Ethiopia

“…In addition, there is a need to undertake continued environmental monitoring and seasonal climate forecasting as a major component of malaria early-warning system. In order to develop a working early-detection and early-warning systems, it is essential to first understand the underlying patterns and scale of malaria occurrence in both time and space [ 60 ]. To this effect, it is paramount important to undertake vulnerability monitoring, environmental monitoring and sentinels case surveillance or cross-sectional surveys [ 61 ].…”

“…To this effect, it is paramount important to undertake vulnerability monitoring, environmental monitoring and sentinels case surveillance or cross-sectional surveys [ 61 ]. As the transmission of malaria may not be synchronized over a wider geographical scale [ 60 ] early-detection and early-warning systems should be instituted at a narrow geographical scale which is to be determined on the basis of sound epidemiological and entomological studies. The early-detection and early-warning systems should also be integrated with dynamic online monitoring products such as climate conditions associated with malaria that are automatically updated when new data are available [ 62 ].…”

Species Diversity and Entomological Inoculation Rate of Anophelines Mosquitoes in an Epidemic Prone Areas of Bure District, Northwestern Ethiopia

“…funestus, had been reported from Gojam [63]. However, it is inconsistent with other reports from Ethiopia, where this species had been recorded in areas below 2,000 m.a.s.l [64,65,66,67]. The occurrence of this species up to 2,157 m.a.s.l could be attributed to the presence of increased temperature as a result of climate change, land cover and land use changes [62,68,69,70].…”

“…Similarly, higher annual overall P. f-sporozoite rate of An. arabiensis has been documented in different parts of Ethiopia [66,76] and elsewhere in Africa [82,94,102,103,104].…”

Trends in Malaria Cases and Stratification of Malaria Incidence in the Malaria Elimination Setting, Harari Region, Eastern Ethiopia

“…About 60% of the population are living in the malaria risky areas mainly areas that lie below 2000 meters above sea level [4,5]. However, several pockets with micro-epidemiological conditions supporting malaria transmission occur in areas above this altitude [6,7]. P. falciparum and P. vivax are the dominant parasites responsible for the majority of malaria cases in Ethiopia.…”