Trichinella isolates: parasite variability and host responses.

The genus Trichinella has the widest geographical distribution and the largest range of host species of all parasitic nematodes. It remains a significant human pathogen. More than 300 isolates of the genus are now available for laboratory study. The taxonomy of the genus, which has only recently achieved some stability, depends upon the use of a variety of biological, biochemical and genetic criteria. The biological characteristics of isolates, particularly those relating to infectivity and pathogenicity, can show considerable variation because they are subject to strong host influences, notably those associated with immune and inflammatory responses. Comparative studies of different isolates in different hosts, particularly strains of inbred mice, have helped to define these influences and to identify the relative contributions of isolate immunogenicity and host immune response capacity to the outcome of infection. Data from such studies can not only contribute to a better understanding of the biology of this genus but can also throw light on fundamental aspects of host-parasite interactions.