Specificity Of infection sites in vertebrate hosts

Abstract

Most myxozoans infecting fish are host-, tissue- and organ-specific parasites. The host specificity of most myxosporean species is rather narrow, with the parasites able to develop in only one host species or in closely related fishes. There are species, however, with relatively wide host ranges, infecting genetically distant host species. Tissue selection is a key taxonomic feature for histozoic myxozoans, as they develop mature spores in only one tissue type. Histozoic species may form plasmodia in epithelial, muscular, cartilaginous and connective tissues, inside nerve cells and in blood vessels, etc. Development of plasmodia often occurs in a well-defined part of an organ. For example in the gills, different species develop in or among lamellae, in different tissues of gill filaments or inside the cartilaginous gill arch. Other species may develop plasmodia in different organs composed of the same tissue type. Using examples, this chapter reviews infection specificity, characterizes howinfections aremanifested in various tissues and organs, and discusses how infections relate to both parasite and host phylogeny.