Microsatellite analysis of pooled Schistosoma mansoni DNA: an approach for studies of parasite populations

L. K. SILVA a1a2a3, S. LIU a1 and R. E. BLANTON a1c1
a1 Center for Global Health and Diseases, 2103 Cornell Road, Case University, Cleveland, OH 44106-7286, USA
a2 Centro Universitário da Bahia (FIB), R. Xingu, 179, STIEP, Salvador, BA 41770-130, Brazil
a3 União Metropolitana de Educação e Cultura (UNIME), Av. Luís Tarquínio Pontes, 600, Centro, Lauro de Freitas, BA 42700-000, Brazil

Article author query
silva lk   [PubMed][Google Scholar] 
liu s   [PubMed][Google Scholar] 
blanton re   [PubMed][Google Scholar] 


Human parasites are often distributed in metapopulations, which makes random sampling for genetic epidemiology difficult. The typical approach to sampling Schistosoma mansoni involves laboratory passage to obtain individual worms with small sample size and selection bias as a consequence. By contrast, the naturally pooled samples from egg output in stool or urine directly represent the genetic composition of current populations. To test whether pooled samples could be used to estimate population allele frequencies, DNA from individual cloned parasites was pooled and amplified by PCR for 7 microsatellites. By polyacrylamide gel analysis, the relative band intensities of the products from the major alleles in the pooled samples differed by 0–6% from the summed intensities of the individual clones (mean=2·1%±2·1% S.D.). The number of PCR cycles (25–40) did not influence the accuracy of the estimate. Varying the frequency of 1 allele in pooled samples from 32 to 69% likewise did not affect accuracy. Allele frequency estimates from aggregate samples such as eggs will be a better foundation for studies of parasite population dynamics as well as the basis for large-scale association studies of host and parasite characteristics.

(Received April 1 2005)
(Revised June 18 2005)
(Revised August 24 2005)
(Accepted August 25 2005)
(October 28 2005)

Key Words: allele frequency; PCR; pooled samples; genetics; metapopulation.

c1 Center for Global Health and Diseases, Case Western Reserve University, 2103 Cornell Rd, Wolstein Research Building, Cleveland, Ohio 44106-7286, USA. Tel: +216 368 4814. Fax: +216 368 4825. E-mail: