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Interactions between natural populations of human and rodent schistosomes in the Lake Victoria region of Kenya: a molecular epidemiological approach.

Steinauer ML, Mwangi IN, Maina GM, Kinuthia JM, Mutuku MW, Agola EL, Mungai B, Mkoji GM, Loker ES - PLoS Negl Trop Dis (2008)

Bottom Line: Schistosoma mansoni exists in a complex environmental milieu that may select for significant evolutionary changes in this species.Peak emergence for S. mansoni cercariae occurred as light became most intense and overlapped temporally with S. rodhaini.Comparison of schistosome communities within snails against a model indicated that the community was structured and that coinfections were more common than expected by chance.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of New Mexico, Albuquerque, New Mexico, USA. mls1@unm.edu

ABSTRACT

Background: Schistosoma mansoni exists in a complex environmental milieu that may select for significant evolutionary changes in this species. In Kenya, the sympatric distribution of S. mansoni with S. rodhaini potentially influences the epidemiology, ecology, and evolutionary biology of both species, because they infect the same species of snail and mammalian hosts and are capable of hybridization.

Methodology/principal findings: Over a 2-year period, using a molecular epidemiological approach, we examined spatial and temporal distributions, and the overlap of these schistosomes within snails, in natural settings in Kenya. Both species had spatially and temporally patchy distributions, although S. mansoni was eight times more common than S. rodhaini. Both species were overdispersed within snails, and most snails (85.2% for S. mansoni and 91.7% for S. rodhaini) only harbored one schistosome genotype. Over time, half of snails infected with multiple genotypes showed a replacement pattern in which an initially dominant genotype was less represented in later replicates. The other half showed a consistent pattern over time; however, the ratio of each genotype was skewed. Profiles of circadian emergence of cercariae revealed that S. rodhaini emerges throughout the 24-hour cycle, with peak emergence before sunrise and sometimes immediately after sunset, which differs from previous reports of a single nocturnal peak immediately after sunset. Peak emergence for S. mansoni cercariae occurred as light became most intense and overlapped temporally with S. rodhaini. Comparison of schistosome communities within snails against a model indicated that the community was structured and that coinfections were more common than expected by chance. In mixed infections, cercarial emergence over 24 hours remained similar to single species infections, again with S. rodhaini and S. mansoni cercarial emergence profiles overlapping substantially.

Conclusions/significance: The data from this study indicate a lack of obvious spatial or temporal isolating mechanisms to prevent hybridization, raising the intriguing question of how the two species retain their separate identities.

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Related in: MedlinePlus

Prevalence (percent of snails infected) of S. rodhaini (top) and S. mansoni (bottom) at various sites in the Lake Victoria basin of Kenya over a 2 year period.Blank spaces indicate that either snails were not present or no collections were made.
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pntd-0000222-g003: Prevalence (percent of snails infected) of S. rodhaini (top) and S. mansoni (bottom) at various sites in the Lake Victoria basin of Kenya over a 2 year period.Blank spaces indicate that either snails were not present or no collections were made.

Mentions: Prevalence of schistosome infection varied spatially and ranged from 0.11–3.65% among positive collection sites (Table 2). Prevalence was the highest for both S. mansoni and S. rodhaini at the Car Wash site, which is an area along the shore of Lake Victoria in the city of Kisumu, Kenya, where a population of car washers earns their living by washing vehicles in the lake and is known to be infected with schistosomes [45]. Schistosoma mansoni was more prevalent and widespread than S. rodhaini which was only present at 7 of the 14 collection sites where S. mansoni occurred, and there were no sites where only S. rodhaini occurred. Total prevalence (added over time) of S. rodhaini was not greater than S. mansoni at any one site, but was more prevalent in 7 of the 169 individual collections at Nawa, Nyabera, Usare Beach, and Lwanda. Seasonal patterns of prevalence were not evident, but prevalence for both species was low between November 2004 and March 2005, and increased between September 2005 and March 2006 (Fig. 3).


Interactions between natural populations of human and rodent schistosomes in the Lake Victoria region of Kenya: a molecular epidemiological approach.

Steinauer ML, Mwangi IN, Maina GM, Kinuthia JM, Mutuku MW, Agola EL, Mungai B, Mkoji GM, Loker ES - PLoS Negl Trop Dis (2008)

Prevalence (percent of snails infected) of S. rodhaini (top) and S. mansoni (bottom) at various sites in the Lake Victoria basin of Kenya over a 2 year period.Blank spaces indicate that either snails were not present or no collections were made.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2291567&req=5

pntd-0000222-g003: Prevalence (percent of snails infected) of S. rodhaini (top) and S. mansoni (bottom) at various sites in the Lake Victoria basin of Kenya over a 2 year period.Blank spaces indicate that either snails were not present or no collections were made.
Mentions: Prevalence of schistosome infection varied spatially and ranged from 0.11–3.65% among positive collection sites (Table 2). Prevalence was the highest for both S. mansoni and S. rodhaini at the Car Wash site, which is an area along the shore of Lake Victoria in the city of Kisumu, Kenya, where a population of car washers earns their living by washing vehicles in the lake and is known to be infected with schistosomes [45]. Schistosoma mansoni was more prevalent and widespread than S. rodhaini which was only present at 7 of the 14 collection sites where S. mansoni occurred, and there were no sites where only S. rodhaini occurred. Total prevalence (added over time) of S. rodhaini was not greater than S. mansoni at any one site, but was more prevalent in 7 of the 169 individual collections at Nawa, Nyabera, Usare Beach, and Lwanda. Seasonal patterns of prevalence were not evident, but prevalence for both species was low between November 2004 and March 2005, and increased between September 2005 and March 2006 (Fig. 3).

Bottom Line: Schistosoma mansoni exists in a complex environmental milieu that may select for significant evolutionary changes in this species.Peak emergence for S. mansoni cercariae occurred as light became most intense and overlapped temporally with S. rodhaini.Comparison of schistosome communities within snails against a model indicated that the community was structured and that coinfections were more common than expected by chance.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of New Mexico, Albuquerque, New Mexico, USA. mls1@unm.edu

ABSTRACT

Background: Schistosoma mansoni exists in a complex environmental milieu that may select for significant evolutionary changes in this species. In Kenya, the sympatric distribution of S. mansoni with S. rodhaini potentially influences the epidemiology, ecology, and evolutionary biology of both species, because they infect the same species of snail and mammalian hosts and are capable of hybridization.

Methodology/principal findings: Over a 2-year period, using a molecular epidemiological approach, we examined spatial and temporal distributions, and the overlap of these schistosomes within snails, in natural settings in Kenya. Both species had spatially and temporally patchy distributions, although S. mansoni was eight times more common than S. rodhaini. Both species were overdispersed within snails, and most snails (85.2% for S. mansoni and 91.7% for S. rodhaini) only harbored one schistosome genotype. Over time, half of snails infected with multiple genotypes showed a replacement pattern in which an initially dominant genotype was less represented in later replicates. The other half showed a consistent pattern over time; however, the ratio of each genotype was skewed. Profiles of circadian emergence of cercariae revealed that S. rodhaini emerges throughout the 24-hour cycle, with peak emergence before sunrise and sometimes immediately after sunset, which differs from previous reports of a single nocturnal peak immediately after sunset. Peak emergence for S. mansoni cercariae occurred as light became most intense and overlapped temporally with S. rodhaini. Comparison of schistosome communities within snails against a model indicated that the community was structured and that coinfections were more common than expected by chance. In mixed infections, cercarial emergence over 24 hours remained similar to single species infections, again with S. rodhaini and S. mansoni cercarial emergence profiles overlapping substantially.

Conclusions/significance: The data from this study indicate a lack of obvious spatial or temporal isolating mechanisms to prevent hybridization, raising the intriguing question of how the two species retain their separate identities.

Show MeSH
Related in: MedlinePlus