Myxozoans exploiting homeotherms

Abstract

Discoveries published in 2007 and 2008 expanded the known host range of myxozoans beyond poikilotherms to include mammals and birds. Here we review records of myxozoans from small terrestrial mammals, waterfowl and those associated with humans, and augment them with data from our ongoing studies. True myxosporean infections—those with active parasite development and sporogenesis—have been recorded for Soricimyxum spp. in central European shrews and Myxidium spp. in North American waterfowl. In all cases, bile ducts within the liver were the nidal tissue and complete life cycles are unknown. Incidental myxosporean infections—the presence of myxospores without parasite development—have been observed in humans, usually in association with the ingestion of infected fish. Clinical presentations of these cases range from no disease (e.g. Henneguya spp.), allergic responses (Kudoa sp.) or acute gastroenteritis (Kudoa septempunctata). Phylogenetically, myxosporean parasites of homeotherms cluster closely with Myxidium and Cystodiscus species known to infect other terrestrial vertebrates (reptiles and amphibians), which suggests a single evolutionary expansion from an aquatic Myxidium-clade ancestor to semi-aquatic and terrestrial hosts and environments. Given the diversity of potential mammalian and avian hosts, we expect additional myxosporean parasites to be discovered with further scrutiny of these homeotherms, especially in sparsely surveyed regions including Africa and South America.