Anopheles vectors species composition, their biting cycle and role of human behaviour in Malaria transmission in an endemic region from Namibia
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Date
2021
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University of Namibia
Abstract
Any vector control effort aimed at reducing malaria burden should be based on an understanding of the malaria vectors’ populations, distribution, and behaviours as they relate to both transmission and response to interventions in place. It is well documented that the composition of malaria vectors changes over time but there has not been up-to-date information about that in Namibia. This study aimed to determine the population dynamics of Anopheline vectors and climatic factors that affect their distribution. It also described their biting behaviour and human social activities and behaviours that might expose them to mosquito bites. To address these objectives, human landing catches were conducted hourly from 19:00 hrs – 07:00 hrs indoors and outdoors for eight consecutive days during 2018/2019 and 2019/2020 malaria seasons in Shadikongoro village, Kavango East region. Mosquitoes collected were identified to species level using both morphological and molecular tools. Concurrently, data on which housing structures offered a high risk of mosquito bites was observed. Meteorological data from the Namibia Meteorological Centre was collected and used to determine the relation between these factors and mosquito abundance. A total of 1958 mosquitoes collected. Of these, 1190 were collected in 2018/19 and 768 in 2019/20. Species identification confirmed the presence of Anopheles arabiensis, An. gambiae s.s. and An. funestus s.s. In the 2018/2019 malaria season, An. arabiensis was the most abundant species, predominating both indoors (n = 334) and outdoors (n = 625). Anopheles funestus s.s was the least abundant species with 10 mosquitoes collected indoors and only one outdoors. During the 2019/2020 season, only An. arabiensis was collected. The statistical comparison showed a difference in species abundance between the two sampling periods (X2 = 24.0, p < 0.008). In the 2018/19 malaria season, both An. arabiensis and An. gambiae s.s. preferred biting outdoors (X2 = 32, p < 0.001; X2 = 25.9, p < 0.001, respectively) than indoors while An. funestus s.s. preferred biting indoors (X2 = 1532.719, p < 0.001). In the 2018/2019 and 2019/2020 malaria seasons, sleeping indoors was associated with a higher risk of mosquito bites (2018/19: OR = 0.62, 95% CI: 0.17 – 0.91, p = 0.02; 2019/2020: OR = 0.32, 95% CI: 0.07 – 1.06, p = 0.008). In 2019/2020, outdoor chatting (OR = 0.70, 95% CI: 0.31 – 1.58, p = 0.01) was a risk factors for mosquito bites. The risk of being bitten by mosquitoes in traditional houses was significantly higher (RR = 0.79, 95% CI: 01.23–6.56, p = 0.001) than in modern (RR = 0.48, 95% CI: 0.07–0.93, p = 0.012) and zinc (RR = 0.15, 95% CI: 0.04–0.63, p<0.06) houses. In 2018/2019, only rainfall had a significant effect on overall abundance (Coeff = 0.33, 95% CI: 0.31 – 1.58, p = 0.01) while in 2019/2020, only temperature had an effect (Coeff = 0.6, 95% CI: 0.12 – 0.88, p = 0.01) on abundance. Given this evidence, there is a need to provide interventions targeting both indoor and outdoor mosquito biting such as mosquito nets and spatial insect repellents, respectively. Mosquitoes are still abundant even when there is no rainfall. Therefore, it is important to spray insecticides that last throughout the year.
Description
A research thesis submitted in fulfillment of the requirements for the Degree of Master of Science (Medical Entomology)
Keywords
Anopheles species composition, Biting behaviour, Human social activities, Malaria