Parasite Taxonomy

Abstract

Endoparasites have been classically subdivided into unicellular protozoan and multicellular helminth parasites. The protozoal parasites based primarily on their locomotory organs were divided into three groups, amoebae, flagellates and ciliates, and a fourth group of non-motile sporozoan parasites. This oversimplified classification has undergone extensive modifications in the last 100 years, although it is still being followed by the clinicians and medical parasitologists. On the other hand, the pathogenic helminths belonging to the Animalia kingdom have survived the onslaught of modern changes, barring minor re-classifications, and still the broad classification of these parasites into nematodes, cestodes and trematodes holds good. This chapter highlights the major classification systems which are being followed by protozoologists, helminthologists and medical parasitologists and the recent changes which have been incorporated during the last few decades.

Case Study

Taxonomical Position of Microspora

The Microspora has traditionally been considered as protozoans, but research findings in the last decade have found otherwise. In the fungal zygomycetes group, the sex locus is a syntenic gene cluster that governs sexual reproduction and comprises a high mobility group (HMG) gene, flanked by a triose phosphate transporter and a RNA helicase gene. The microsporidian genomes harbour a sex-related locus with the same genes in the same order. Moreover, genome-wide analysis of synteny reveals multiple other loci common to microsporidia and zygomycetes. These findings support the hypothesis that microsporidia are true fungi that descended from a zygomycete ancestor and suggest the microsporidia may have a genetically controlled sexual cycle. On the basis of these findings, Microspora is no longer considered a protozoan parasite but is designated as a fungus.

• 1. Give one or two examples where similar re-classification of parasites has been made.

• 2. Describe the methods available for identifying a new parasite which shows some similarity with a known parasite.

• 3. Define a hybrid parasite. Name one common parasite which exhibits this feature.

Research Questions

• 1. Like microsporidium, are there other protozoa which do not belong to the parasite group, but belong to fungi or some hitherto unknown group?

• 2. Is it possible to separate some algal forms, euglenids and dinoflagellates from protozoa which have totally different biology?

• 3. How can one create a more refined taxonomy of helminths based on the newer methods of classification?