Malaria and Water Resource Development - Recent Advances and Issues in Environmental Science - page 168

DISCUSSION
In this study, after controlling for age, sex, and time, the prevalence of P. vivax (7.7%)
in children who reside within 3 km of the reservoir created by the Gilge-Gibe hydro-
electric dam was significantly higher than in children living in more distant villages
(4.4%) although the villages have a similar eco-topography. Plasmodium falciparum
prevalence rates in “at-risk” communities (5.4%) were higher than in “control”
communities (2.2%), but the difference showed no statistical significance (p-value
= 0.085). Overall, the Plasmodium prevalence near the reservoir was statistically
higher as compared to the Plasmodium prevalence in more distant communities (p-
value = 0.013). The main reason for the higher prevalence of malaria among children
living close to the reservoir may be due to the man-made ecological transformations,
which may influence the presence of mosquito-breeding site and might have an im-
pact on the behavior, parity rate and longevity of malaria vectors of the study area. A
similar study in Cameroon showed a malaria prevalence of 36% in residents living in
close proximity to a man-made lake compared with a prevalence of 25% in a village
14 km away [36]. In India, a 2.4-fold increase in malaria cases and an over 4-fold
increase in annual parasite incidence were recorded among children in villages close
to a reservoir as compared to more distant villages [37]. A high malaria prevalence,
up to 47%, was recorded around the Mantali dam in Senegal, constructed to provide
hydropower and irrigation, compared to prevalences of 27.3% and 29.6% in two
communities downstream the dam [38]. Risk factors for malaria infections in the
Gilgel-Gibe area might be proximity to the dam, as the low socioeconomic status, the
health infrastructure and the malaria control methods appear to be similar in “at-risk”
and “control” communities.
This study indicates that children between the age of 1 and 4 years tend to have
a higher malaria prevalence than children below the age of 1 year (p-value = 0.083,
non-signifi cant for P. vivax and P. falciparum together). This could be because the
older children, in contrast to younger children, spend outdoors in the evening when
peak biting activities of malaria vector mosquitoes are high or the greater use of anti-
malarial drugs in early childhood [39]. A similar study in Gabon showed lower ma-
laria prevalence in children less than 6 months (3.7%) than in children at the age of
47 months (47.5%) [40], which was attributed to low number of children less than 1
year of age and immunity acquired from mothers as difference in the risk of infection
among different age groups could be associated to differences in the immunological
status. The risk of infection fi rst increases with age and then decreases when the indi-
vidual reaches a certain degree of immunity due to exposure to the parasite. This was
indicated in the study reported in this chapter as well. Plasmodium prevalence rates in
children between 1 and 4 years, below 1 year and children age of 5-9 years showed no
statistically signifi cant differences.
According to several reviews, P. falciparum is the dominant species in Ethiopia,
followed by P. vivax , accounting for 60% and 40% of all malaria cases, respective-
ly [16, 41]. In the present study, the predominant species was P. vivax followed by