Reconstructing Colonization Dynamics of the Human Parasite Schistosoma mansoni following Anthropogenic Environmental Changes in Northwest Senegal.
BACKGROUND
Anthropogenic environmental changes may lead to ecosystem destabilization and the unintentional colonization of new habitats by parasite populations. A remarkable example is the outbreak of intestinal schistosomiasis in Northwest Senegal following the construction of two dams in the '80s. While many studies have investigated the epidemiological, immunological and geographical patterns of Schistosoma mansoni infections in this region, little is known about its colonization history.


RESULTS
Parasites were collected at several time points after the disease outbreak and genotyped using a 420 bp fragment of the mitochondrial cytochrome c oxidase subunit 1 gene (cox1) and nine nuclear DNA microsatellite markers. Phylogeographic and population genetic analyses revealed the presence of (i) many genetically different haplotypes at the non-recombining mitochondrial marker and (ii) one homogenous S. mansoni genetic group at the recombining microsatellite markers. These results suggest that the S. mansoni population in Northwest Senegal was triggered by intraspecific hybridization (i.e. admixture) between parasites that were introduced from different regions. This would comply with the extensive immigration of infected seasonal agricultural workers from neighboring regions in Senegal, Mauritania and Mali. The spatial and temporal stability of the established S. mansoni population suggests a swift local adaptation of the parasite to the local intermediate snail host Biomphalaria pfeifferi at the onset of the epidemic.


CONCLUSIONS
Our results show that S. mansoni parasites are very successful in colonizing new areas without significant loss of genetic diversity. Maintaining high levels of diversity guarantees the adaptive potential of these parasites to cope with selective pressures such as drug treatment, which might complicate efforts to control the disease.
Department of Biology, University of Leuven, Leuven, Belgium; Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.
Frederik
F
Van den Broeck
Department of Biology, University of Leuven, Leuven, Belgium; College of Marine and Environmental Sciences, James Cook University, Townsville, Australia.
Gregory E
GE
Maes
Department of Biology, University of Leuven, Leuven, Belgium; Department of Imaging and Pathology, University of Leuven, Leuven, Belgium.
Maarten H D
MH
Larmuseau
Division of Life Sciences, Natural History Museum, London, United Kingdom.
David
D
Rollinson
UFR Pharmacy, University of Caen Basse-Normandie, Caen, France.
Ibrahima
I
Sy
Santé Plus, Dakar, Senegal.
Djibril
D
Faye
Department of Biology, University of Leuven, Leuven, Belgium.
Filip A M
FA
Volckaert
Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium.
Katja
K
Polman
Department of Biology, University of Leuven, Leuven, Belgium; Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium; Department of Biology, Royal Museum for Central Africa, Tervuren, Belgium.
Tine
T
Huyse
D000818:Animals; D001499:Bayes Theorem; D016000:Cluster Analysis; D018509:DNA, Helminth; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D004777:Environment; D015971:Gene Expression Regulation, Enzymologic; D014644:Genetic Variation; D006802:Human Activities; D006801:Humans; D018895:Microsatellite Repeats; D058974:Phylogeography; D011157:Population Dynamics; D012550:Schistosoma mansoni / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D012555:Schistosomiasis mansoni / Q000453:epidemiology / Q000469:parasitology*; D012675:Senegal / Q000453:epidemiology
D018509:DNA, Helminth; D003576:Electron Transport Complex IV