Transmission Of myxozoans to vertebrate hosts

Abstract

This chapter reviews how waterborne myxozoan stages achieve transmission to vertebrate hosts, a process that depends on attachment to a host and subsequent invasion. Such transmission has largely been examined for actinospores that are produced by myxosporeans infecting annelid hosts, but we also consider malacosporean stages released from freshwater bryozoan hosts where possible. We review the functional morphology of spores and how this relates to the invasion process and consider cues that initiate the discharge of polar capsule filaments for attachment and sporoplasm activation. We summarize initial invasion steps and discuss factors that may influence transmission ranging from spore viability and infectivity to host cues. We also describe what is known about portals of entry to fish hosts and how non-specific host recognition may enable some myxosporeans to infect a broad range of hosts. Such non-specificity could promote diversification if speciation follows the acquisition of new hosts. We conclude by recommending experimental procedures to be adopted when handling and harvesting actinospores for experimental studies.