Malaria Vectors and Transmission Intensity in an Epidemic Prone Area of Bure District, West Gojam, Northwestern Ethiopia
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Date
2018-04-04
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Addis Ababa University
Abstract
Malaria is one the leading health problem in Ethiopia. In the past few decades’ places
located above 2,000 meters elevation were considered as malaria free areas. However,
the major malaria epidemics were seen up to 3,000 meters due to climate and land-use
changes (ecological changes). Currently, due to the mass distribution of long lasting
insecticide treated nets (LLINs) and nationwide implementation of Artemisinin Based
Combination Therapy (ACT) and case management, the reduction of malaria morbidity
and mortality have observed throughout Ethiopia. Regardless of these tremendous
efforts, still malaria is one of the health problems of some highland parts of the country.
In the study area, there was no any information on the diversity, abundance and spatiotemporal
distribution of both the adult and larva of Anopheles mosquitoes. Hence, the
objective of this study was aimed to investigate the species composition and abundance,
blood feeding pattern, parous rates, longevity, entomological inoculation rates of
Anopheles mosquitoes in Bure district, Northwestern Ethiopia. Similarly, species
composition and distribution of the larva of Anopheles were studied and habitats were
identified and characterized in each month. Entomological study of Anopheles
mosquitoes was conducted longitudinally in each month, from July 2015 to June 2016 in
three villages, Bukta, Workimdr and Shnebekuma. Adult Anopheles mosquitoes were
collected by Light Traps, Pyrethrum Spray Catches and Artificial Pit Shelters.
Identification of Anopheles species was done using morphological keys and speciesspecific
polymerase chain reaction. Parous rates were determined by dissecting of the
abdomen of unfed mosquitoes and then longevity was calculated from parous rates (p)
using . Blood meal origins and circumsporozoite proteins were analyzed by
Enzyme-Linked Immuno Sorbent Assay (ELISA). The human blood index (HBI) was
calculated as the proportion of the mosquitoes fed on human blood meal of the total
mosquitoes tested. Sprorozoite rate was expressed as the proportion of mosquitoes with
Circum-sporozoite protein (CSP) to the total numbers of mosquitoes tested. Larvae were
collected from different breeding habitats using 350ml white dipper (and graduated
pipette) and habitats were characterized; and morphologically 3rd and 4th stages of these
larvae were identified to species level using keys from July 2015 - June 2016.
Independent-Samples T-Test and One-way- ANOVA were applied to evaluate
mosquitoes densities difference between villages and species, indoor and outdoor host
seeking mosquitoes, overall human and bovine blood indices and environmental
variables. Nine adult species were identified (Anopheles demeilloni, An. arabiensis, An.
funestus, An. coustani, An. squamosus, An. cinereus, An. pharoensis, An. rupicolus, and
An. natalensis). Of 4703, An. demeilloni (50.7%, n = 2383) was the most dominant than
others (p < 0.05). Spatially, the largest numbers of adult Anopheles mosquitoes were
collected in non-irrigated village (Shnebekuma) (2.39 ± 0.10 adults/CDC-LT) than
irrigated (Bukta) (1.35 ± 0.11 adults/CDC-LT) (p < 0.05). The overall (single plus
mixed) HBIs of An. arabiensis, An. funestus, An. coustani, An. squamosus and An.
cinereus were equal to the overall BBIs of the correspondent species (p > 0.05). The
CSP-ELISA test revealed that only sporozoite infected Anopheles mosquitoes were
found only in non-irrigated villages (Shnebekuma and Workmidr). Overall sporozoite
rates of An. funestus, An. coustani, An. arabiensis for P. vivax and P. falciparum were
0.57%, 0.23% and 0.2%, respectively. Morphologically, seven species of Anopheles
larvae were identified (An. demeilloni, An. gambiae s.l, An. funestus s.l, An. coustani s.l,
An. squamosus, An. cinereus and An. pharoensis). Of 3490, An. demeilloni (34.8%) was
the most dominant than others (p < 0.05). The density of Anopheles larva was
statistically insignificant in the three villages (p > 0.05). In conclusion, three of the most
important malaria vectors of Ethiopia were identified; An. arabiensis, An. funestus and
An. pharoensis. Most of the adults and sporozoite infected Anopheles mosquitoes were
found only in non-irrigated villages. All these results implying that, irrigation activity has
not any influence on the abundance, composition of Anopheles mosquitoes and
prevalence of malaria in the three villages. Generally, vectors infection and malaria
transmission rates were very low. Thus, breeding habitat management must be in
incorporated into control program and applied throughout the year together with LLINs
and IRS, especially for non irrigated villages.
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Keywords
Bure District, An. Coustani, Irrigation, Sporozoite Rate, Larval Habitats, IRS