microsporidia have been grouped into five classes depending on their molecular traits, a higher level of classification using SSU (small subunit) rDNA analysis. However molecular data is still lacking for several genera of microsporidia. Xenomas found in other organisms Whilst xenomas are more highly characteristic of fish, they can be quite extensive in other organisms including crustaceans, insects, oligochaetes and other vertebrates. Microsporidian xenomas that develop in fish can also occur in crustaceans. Roughly 43 microsporidian genera have been found to infect crustaceans, with at least 23 microsporidian species found in shrimp, most of them infecting muscular tissue. Other species also infect the digestive tract, reproductive organs and their hepatopancreas. Xenoma-like formations have also been found in species of shrew caused by Soricimyxum fegati, a type of myxosporea, showing they can also occur in mammals. Treatment The host can eventually destroy the xenoma. Proliferative inflammation occurs in mature xenomas and transforms them into granulomas. Granuloma involution then ensues where phagocytosis kills the spores. Studies have shown it is possible to vaccinate against xenomas. One study showed that developing a vaccine using a 103 to 105 dose of killed spores from a low-virulence strain of Loma salmonae resulted in rainbow trout producing 85% less xenomas in their gills after experimental infection (compared to the control). This ultimately offers much improved protection to microsporidial gill disease which is common amongst rainbow trout. Therapeutic drugs have proved ineffective at treating this disease and harvesting whole-spores is a relatively easy technique. See also Microsporidia Glugea Spore References Microsporidia Fish diseases Tumor