Rapid Sequencing of Parasite rRNA

The phylogeny of a large number of parasite species is still entirely based on morphological and physiological features. However, the reliability of such criteria becomes highly questionable, especially for species exhibiting a low level of organismal complexity. The advent of modern nucleic acid sequence technology now provides the opportunity for critical reexaminations of existing taxonomies and for improved measurements of phylogenetic distances (1 ). Nucleotide sequence comparisons not only furnish a rich amount of information, but their one-dimensional character also makes them much less susceptible to subjective judgements and particularly well suited to quantitative evaluation. Over recent years the accumulation of sequence data on ribosomal genes from a variety of prokaryotic and eukaryotic species has revealed the outstanding properties of rRNAs as molecular indicators of phylogenetic relationships (1 , 2 ). Their remarkable interest stems not only from their universal occurrence in all organisms, or from the high information content of their nucleotide sequence, but also from their mosaic pattern of structural variation, with an interspersion of domains showing significantly different rates of sequence divergence (3 –5 ). Owing to the presence of a series of highly conserved domains, rRNAs can serve as general indicators, even among the most distant living species (6 –11 ).