1. Empirical Evidence for Host-Parasite Coevolution Rebecca Schmidt

2.  Serves as a model for pathogen response to selective pressure  This is increasingly important as we experience more instances of drug resistance  Plant resistance to insects and insect resistance to insecticides

3.  Variation within host and parasite traits  The fitness of both populations is affected  More clearly seen in specialized parasites Schistosomes are prime candidates for study

4.  Phylum: Platyhelminthes  Class: Trematoda  Parasitic worms  Adults are 10-20 mm long

5.  World Health Organization: second in importance only to malaria  200 million infected world- wide  Diarrhea and enlargement of the spleen and liver

6.  In long-term disease, damage to lungs, spleen, liver, brain, spinal cord, pancreas, and heart muscle may cause death

8. Corresponding Author: Joanne P. Webster

9.  Schistosoma mansoni  Intermediate host: Biomphalaria glabrata snails  Definitive host: mice

10.  R-line: Artificially selected schistosome- resistant snails  U-line: Wild-type snails  R:U line: Mixed population  Snails were kept in tanks, with four tanks of 20 individuals per condition

11. 1. 100 miracidia dose added to tank 2. Cercariae from all snails harvested 3. Mice exposed to 220 cercariae 4. Mouse liver and spleen removed

12. 5. Organs placed in conditions to stimulate hatching 6. New snails from parental lines exposed to new miracidia harvested from mice  Four total generations

13. 1. 20 worms and 10 snails were randomly selected from each generation 2. Genetic structure analyzed using 6 S. mansoni and 8 B. glabrata microsatellite markers 3. PCR performed

14.  Infection rate was higher in the U-line than the R and R:U-lines (p=0.0006)  Infection rate increased with generation in the R-line (p=0.04)  Infection rate decreased non-significantly with generation in the U-line

15. % snails infected Generation 1234 Infectivity

16.  Virulence declined with generation in R-line snails (p=0.04)  No trend in other two conditions

17. Generation 1234 % snail mortality Virulence

18.  Infectivity to mouse was lower in parasites passed through R-line snails (p=0.010)  Infectivity increased through generations in the R-line snails (p=0.06)  Virulence did not differ with respect to generation or snail condition

19. Infectivity

20. Virulence

21.  Clustering based on generation and line  R lines separate from R:U and U lines, with the last generation being most different

22.  No clear clustering by generation  R lines cluster separately from R:U and U

23.  B. glabrata (snails) can rapidly counter-adapt to parasite changes  S. mansoni (schistosomes) can rapidly counter-adapt to host changes  Previously suggested methods of schistosome control may be ineffective

24.  Resistance to the drug of choice  Development of resistance to new drugs  What can be done to treat and prevent schistosomiasis?

25. Alternatives and challenges Corresponding Author: Rashad Abdul-Ghani

26.  Typical drug of choice  Resistant strains of S. mansoni found in Egyptian and Sengalese patients  Cause of resistance unclear  Substitutes are needed

27.  Drug of choice in Brazil  Extremely resistant strains of S. mansoni have been found in Brazil

28.  Myrrh (Mirazid  )  Trioxolanes  Artemisinin derivatives

29.  Malaria treatment  Prophylactic  Can cause resistance to reinfection  Superior to current vaccine candidates

30. Challenges and Prospects Corresponding Author: Alan Fenwick

31.  Molluscicides  Introduction of competitor species  Vaccines  Water-resource development

32.  Affect more than snails  Not sustainable  Not effective in large water bodies  High expense

33.  Louisiana red swamp crayfish in East Africa  Other snails in the Caribbean islands

34.  Several candidates, none successful  Large genome (280 Mb)  Makes antigen identification difficult

35.  The only complete prevention  Cleaner irrigation methods  Clean drinking water  Sanitary removal of waste

37. Abdul-Ghani, R., Loutfy, N., El Sahn, A., Hassan A. 2009. Current chemotherapy arsenal for schistosomiasis mansoni: alternatives and challenges. Parasitology Research 104: 955- 965 Fenwick, A. Rollinson, R. and Southgate, V. 2006. Implementation of human schistosomiasis control: challenges and prospects. Advances in Parasitology 61: 568- 622 Webster, J.P., Shrivastava J., Johnson, P.J., and Blair, L. 2007. Is host-schistosome coevolution going anywhere? BMC Evolutionary Biology 7

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