Discussion

Parasitology has been transformed by genome sequencing. Comparisons across genomes have addressed questions at different levels and identified candidate genes for detailed follow-up. Sets of genes have been defined that are conserved over different evolutionary distances as well as extremely divergent genes with restricted distributions. The Plasmodium genus is the best example of where a comparative approach has been applied. Comparisons have encompassed all human-infective species, plus selected relatives from rodents, non-human primates, and birds, and have revealed the strikingly differences in the composition and organisation of highly divergent multigene families. Fine-grained comparisons within a single sub-genus have given us the clearest picture yet of how a parasite of humans has arisen. In contrast, the large and complex genomes of helminths have presented technical and economic challenges that in most cases have limited the availability and accuracy of genome assemblies. Nevertheless, genomes have now been individually described for 40 helminth species and in a few clades, with higher-accuracy genomes, comparative genomics approaches have revealed genes associated with parasitism. We have used published, as well as new, genome data to create a large comparative genomics dataset that samples the diversity across platyhelminths and nematodes. By covering multiple species, potential problems of fragmentary data have been avoided to reveal patterns of metabolic differences across multiple lineages, possible new drug targets, and lineage-specific multigene families. As with protozoan studies, changes to sequencing technologies are opening new opportunities to delve deeper and reveal genes associated with the evolution of individual parasite species.