Studies on the Anopheline Mosquitoes of Metehara and \ Surrounding Areas in Relation to Malaria Transmission
No Thumbnail Available
Date
2001-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
The ecology and behaviour of Anopheles mosquitoes was studied in four selected sites in
the Metehara area, Upper Awash Valley, Eastern Ethiopia. The sites represented two insecticide
unsprayed villages (Metehara and Gelcha) and two sprayed villages (the Sugar Estate and Buse).
Information on the prevalence of malaria cases was also gathered from the Metehara Sugar
Estate Hospital and the East Shoa Malaria Control Sector (Nazareth). The results showed that a
total of 24,799 microscopically diagnosed malaria cases out of 68,000 blood samples were
registered between July 1999 and September 2000 in the two health service rendering
organizations. Plasmodium falciparum and P. vivax were found to be responsible for the disease
and occur nearly in equal proportions (52.7% P. falciparum and 47.3% P. vivax ).
Larval collections from the different breeding habitats revealed the presence of four
species of which Anopheles arabiensis was the predominant followed by. An. pharoensis.
Similarly, a total of 3639 adult anophelines representing at least eight species were caught using
different methods from July 1999 to September 2000. An. arabiensis was the predominant
species, forming 95% of all collections followed by An. pharoensis (3.8%).
The density of An. arabiensis resting indoors in the sprayed sites was much lower than
the density in the unsprayed sites. Consequently, 18%, 21.3%, 66.1% and 69.4% of An.
arabiensis exhibited exophily in Gelcha, Metehara, Buse and the Sugar Estate, respectively.
The indoor to outdoor biting ratio of An. arabiensis varied between villages: 0.53 in the
Sugar Estate, 1.97 in Buse, 0.75 in Gelcha and 2.12 in Metehara town, showing that the species
was more endophagic in Buse and Metehara and more exophagic in Gelcha and the Sugar Estate,
*
:
XI
The highest man biting rate of 39.5, was recorded in Metehara town and the lowest 8.4 in Buse.
An. pharoensis was mostly an outdoor feeder.
Of 864 An. arabiensis and 63 An. pharoensis dissected from human bait collections, the
average parous rate was 45.1% and 30.2%, respectively, showing An. arabiensis to be longerlived
than An. pharoensis. The sporozoite rate of An. arabiensis was 0.77% in parous and 0.21%
in nulliparous population, the overall being 0.46%. Similarly, An. pharoensis had sporozoite rate
of 5.3% in parous and 2.3% in nulliparous population, the overall being 3.2%. The biting rhythm
of An. arabienisis exhibited two to three peaks of activity before and after midnight . The highest
biting density occurred after midnight indoors while variation was observed outdoors.
The average daily entomological inoculation rate (EIR) of An. arabiensis was 0.05 while
that of An. pharoensis was 0.01.
The Human blood index (HBI) of An. arabiensis revealed variation between
sites/villages being 1 in Metehara, 0.47 in Gelcha, 0.85 in Buse and 0.93 in the Sugar Estate, the
overall being 0.65. The HBI varied also between dwelling conditions of mosquito sampling,
being highest in human dwellings (0.78) and lowest in animal shelters (0.13) showing the
opportunistic feeding behaviour of An. arabienisis.
Clearly, An. arabiensis is the most important vector and An. pharoensis a secondaiy
vector of malaria in the Metehara area.
Insecticide susceptibility studies in Metehara showed that 30% arid 25% of An.
\
arabiensis was resistant to DDT and pennethrin , respectively. The level of DDT and permethrin
resistance in An. arabiensis does not seem to be epidemiologically dangerous, but requires
frequent monitoring. An. arabiensis was found to be highly susceptible to propoxur (carbamate
insecticide) .
Description
Keywords
Studies on the Anopheline, Mosquitoes of Metehara