Assessment of Species Composition and Ecology of Eye-Seeking Flies (Diptera: Muscidae) in Relation to Trachoma Transmission in South Gondar, North West Ethiopia.
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Date
2004-04
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Addis Ababa University
Abstract
The study was conducted in South Gondar Zone, DelTa Woreda, Zara-Jigina kebele and
Melefena village from December 2002 to March 2003. FOliy households were selected at
random from the village and one child between 2-10 years old was recruited for the study.
Attempts to quantity flies swanning the faces of children were made by simply counting and
collecting flies using hepa-filter aspirator. To detelmine the general trend of the diumal fly
activity, the sum of the number of flies counted/collected from each child during each hour
of the day was averaged and plotted against time of observation.
Data were also obtained from the heads of households for h•achoma risk factor analysis using
a prepared questionnaire. Different animal excreta including human faeces and house garbage
were investigated to dete1mine the breeding sites of eye-seeking flies under natural conditions
in the field using funnel cage exit traps. Finally an ophthalmic nurse for the presence or
absence of h•achoma screened the study children by everting the upper eyelids and visually
examining the tarsal plate with a torch and a 2.5 X magnitying binocular loupe. Eyes were
graded according to Thylefors et al. (1987) simplified scale. All the trachoma positive
children were given 1 % tetracycline eye oinhnent and health education was given to the
community.
The study showed that most (about 94.5 %) of the flies captured on the faces of
children were found to be Musca sorbells. Musca d011lestica accounted for 2.2 % and the
remaining (3.3 %) were unidentified Musca species. The main breeding habitat for M sorbells
was found to be human and dog faeces. The peak density of flies on the faces of children was
observed in the moming between 09:00 - 11 :00 hours. Temperature and relative humidity
were found to be the two impollant environmental factors goveming the diurnal activity of
flies. The highest fly density was observed in a temperahlre range of 23 to 27°C, and 32 to 35
% relative humidity. During the four-month Shldy, the lowest density of flies was observed in
December 2002 and highest in Febmaty 2003. Logistic regression analysis on the risk factors
of trachoma have shown that trachoma is directly related with sex, age, education, household
size, number of children below the age of 10 years, cohabitation with cattle, fly density, and
face drying. Seventy-five percent of the study children were infected with trachoma.
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Biology