Population genetics

We are determining whether different schistosomiasis treatment programmes are influencing the population genetic structures of schistosome species.

There is only one effective anti-schistosomal drug, Praziquantel (PZQ). Disease control programmes in sub-Saharan Africa rely heavily on PZQ, raising concerns of drug resistance in the parasite population.

Schistosomiasis egg

Schistosoma mansoni egg.

We are trying to determine whether drug resistance is an issue in schistosomiasis treatment regimes. While we currently do not know of any specific genetic markers of resistance in schistosomes, we can use other genetic markers and population genetics to monitor changes.

Studying drug resistance

The aim of this study is to determine the impact of contrasting disease control strategies on schistosome population genetic diversity and structure in two species of parasite: Schistosoma mansoni and Schistosoma haematobium, in Tanzania and Niger respectively.

In each location we are testing several different treatment strategies (arms) for cost effectiveness and control success. The regimes vary in treatment intensity and frequency.

Treatment regimes

Tanzania schistosomiasis

CWT = Community Wide Treatment       SBT = School Based Treatment

In Tanzania six differential treatment arms are being tested. We are undertaking parasite population genetic monitoring in the two most extreme treatment pressure arms.

  • Arm 1: Highest treatment pressure, annual community-wide treatment
  • Arm 6: Lowest treatment pressure, school-based treatment biennially
Niger schistosomiasis

CWT = Community Wide Treatment        SBT = School Based Treatment

In Niger six differential treatment arms are being tested. We are undertaking the parasite population genetic monitoring in the four most extreme treatment pressure arms.

  • Arm 1: Community-wide two annual treatments
  • Arm 2: Community-wide one annual treatment
  • Arm 5: School-based two annual treatments
  • Arm 6: School-based one annual treatment

Parasite surveys

Miracidium

Miracidium of S.mansoni.

Sampling

In selected schools we collect parasite samples (miracidia stage) from infected children. Individual miracidia are then analysed and their DNA is compared. This data is then used to determine genetic diversity and population structure within the same species.

We will compare genetic diversity between pre and post-treatment samples and between the different treatment arms, using indices such as:

  • allelic richness
  • number of alleles per locus
  • number of private alleles
  • observed and expected heterozygosity.

Results

Preliminary results

We have completed two years of miracidia collections from our study sites in Tanzania and Niger. All samples have been entered into the Schistosomiasis Collection at the Natural History Museum (SCAN) database.

We have optimised species-specific microsatellite multiplex panels for S. haematobium (18 loci) and S. mansoni (20 loci) and have started genotyping baseline miracidia.

Research leader
Dr David Rollinson
Dr David Rollinson

Individual Merit Researcher in parasitology and Director of WHO Collaborating Centre. Research interests include schistosomes and their snail vectors. 

Project staff
Anouk Gouvras
Dr Anouk Gouvras

Post-doctoral Researcher studying the genetic diversity and epidemiology of human schistosomes and their snail intermediate hosts.

External collaborators
  • Prof Joanne Webster (School of Public Health, Imperial College London)
  • Dr Bonnie Webster (School of Public Health, Imperial College London)
  • Dr Safari Kinung’hi (National Institute For Medical Research, Tanzania)
  • Dr Amadou Garba (Reseau International: Schistosomes, Environment, Amenagement et Lutte, Niger)
  • Dr Amina Garba (Reseau International: Schistosomes, Environment, Amenagement et Lutte, Niger)

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