Host response, parasitic protozoa

Other contributions to this book have taken a molecular view of parasitic nematodes, yet molecules make only a rather brief appearance here. This chapter has tried to show that parasitic nematodes are fascinatingly and tantalizingly diverse at a phenotypic level. It has focused particularly on diversity in phenotypes that are apparent in response to environmental conditions within or outside a host. The interaction of parasites with within-host factors is a major current research effort. However, helminth immunology is particularly notable for its inattention to diversity, especially when compared with the immunology of parasitic protozoa (Read and Viney, 1996). Observations of the interaction of host immunity with subsequent development in S. ratti show the potential power of such interactions. It is also clear that a principal mechanism of the action of host immune responses is against nematode fecundity (Stear et al., 1997). This is likely to be a molecularly complex interaction. Understanding this interaction, as well as variation in the interaction is interesting, but could also form the basis of control by transmission-reduction rather than eradication per se. 

The modern period of chemotherapy, the treatment of disease by use of chemical substances, began with the work of Paul Fhrlich (1854-1916). It was known at the beginning of the present century that certain organic compounds of arsenic would kill protozoa, parasitic micro-organisms responsible for certain diseases, and Ehrlich set himself the task of synthesizing a large number of arsenic compounds, ill an effort to find one which would be at the same time toxic (poisonous) to protozoa irj the human body and non-toxic to the human host... 

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