Abstract
The genomes of more than 20 helminths have now been sequenced. Here we perform a meta-analysis of all sequenced genomes of nematodes and Platyhelminthes, and attempt to address the question of what are the defining characteristics of helminth genomes. We find that parasitic worms lack systems for surface antigenic variation, instead maintaining infections using their surfaces as the first line of defence against the host immune system, with several expanded gene families of genes associated with the surface and tegument. Parasite excretory/secretory products evolve rapidly, and proteases even more so, with each parasite exhibiting unique modifications of its protease repertoire. Endoparasitic flatworms show striking losses of metabolic capabilities, not matched by nematodes. All helminths do however exhibit an overall reduction in auxiliary metabolism (biogenesis of co-factors and vitamins). Overall, the prevailing pattern is that there are few commonalities between the genomes of independently evolved parasitic worms, with each parasite having undergone specific adaptations for their particular niche.
Highlights
Parasitic worms cause some of the most devastating threats to human health and livelihoods
Evidence emerging from genomes supports this, showing that excretory/ secretory (ES) signals change often, resulting in each species having a unique set of ES products
Helminths do not have obvious systems for antigenic variation, similar to those of viruses, bacteria and single-cell parasites, but they have evolved a rich set of effector proteins, other immunomodulatory methods, and they are using a multitude of surface-modification methods, including cellular and acellular encystment, which allows them to persist in the host for decades
Summary
The genomes of more than 20 helminths have been sequenced. We perform a meta-analysis of all sequenced genomes of nematodes and Platyhelminthes, and attempt to address the question of what are the defining characteristics of helminth genomes. Parasite excretory/secretory products evolve rapidly, and proteases even more so, with each parasite exhibiting unique modifications of its protease repertoire. Endoparasitic flatworms show striking losses of metabolic capabilities, not matched by nematodes. All helminths do exhibit an overall reduction in auxiliary metabolism (biogenesis of co-factors and vitamins). The prevailing pattern is that there are few commonalities between the genomes of independently evolved parasitic worms, with each parasite having undergone specific adaptations for their particular niche
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