Genetic Diversity, Multiplicity of Infection and Population Structure of Schistosoma mansoni Isolates of Ethiopia within Human Hosts
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Date
2011-10
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Addis Ababa University
Abstract
Schistosomiasis is a chronic parasitic disease, affecting over 200 million people and
causing over 300,000 deaths per year mainly in sub-Saharan Africa. Strains from the
same or different geographical locations have shown differences in egg production,
infectivity, pathogenicity and susceptibility to chemotherapy. The objective of this
study was to assess the dynamics, genetic polymorphism and structure of Schistosoma
mansoni isolates from four endemic foci in Ethiopia. In a cross-sectional study
involving 1,073 study participants from Kemissie (10°43'30''N, 039°04'20''E), Wondo
Genet (07°05'35''N, 038°36'66''E), Ziway (07°56'37''N, 038°43'25''E), and Sille-Elgo
(05°28'39''N, 037°26'02''E), stool specimens were collected and examined for
Schistosoma mansoni infection using Kato method. Stool specimens were again
collected from 91 positive individuals for molecular studies. The overall prevalence and
intensity of Schistosoma mansoni infection from study subjects of Kemissie, Wondo
Genet and Ziway was found to be 60.48% and 273 eggs per gram of stool, respectively.
Out of 288 miracidia genotyped at a molecular level, 164 unique alleles were counted
for all the 11 loci typed from Kemissie (127), Sille-Elgo (102), Wondo Genet (123) and
Ziway (94). At a population level, the mean number of alleles per locus, allelic richness,
expected heterozygosity in Hardy–Weinberg equilibrium and pairwise FST values
ranged from 8.5 to 11.5, 3.46-20.8, 0.66–0.73 and 3.57–13.63%, respectively. The
Bayesian structuration showed 67.5-87.3% genetic differentiation of the study
populations. The PCA and the Bayesian STRUCTURE had shown four clusters of
population. Generally, high level of genetic diversity and population differentiation
characterized the S. mansoni isolates of Ethiopia. Genetic diversity and multiplicity of
infection with Schistosoma mansoni isolates among and within individual subjects from
the four endemic areas of Ethiopia at infrapopulation level also showed a value of 3.09
to 7.55, 1-1.96, 0.59–0.73 and 0.1763–0.4989, mean number of alleles per locus, allelic
richness, expected heterozygosity in Hardy–Weinberg equilibrium and FIS, respectively.
Mean estimated genetically unique adult worm pairs within hosts ranged from 66-92%
revealing the occurrence of infection of a single host with multiple S. mansoni strains.
The data also indicated the occurrence of inter- and intra-host genetic variations. Based
on previous suggestions about the East African origin of S. mansoni, the present study
enabled us to speculate that Ethiopia could be the probable country of origin for schistosomes. However, definite conclusion requires further investigation using other
genetic markers.
Key words: Ethiopia, Schistosoma mansoni, Microsatellite, Genetic diversity,
Population structure
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Keywords
Ethiopia, Schistosoma mansoni, Microsatellite, Genetic diversity, Population structure