Xenoma
A paper published in 1922 by Weissenberg came up with the term 'xenon' for the xenoparasitic complexes he observed on sticklebacks caused by Glugea anomala, before eventually changing it to xenoma (xenon was already the name of a newly discovered chemical element).
Scientists observed them in several organisms, of which the infection would have varied host cell specificity, ultimately leading to different cellular consequences.
[1] For example, the dinoflagellate protist Sphaeripara catenata induces hypertrophy, polyploid nuclei formation whilst forming a thick-walled hyposome where rhizoids extend into the cytoplasm for nutrient absorption in the appendicularian Fritillaria pellucida.
[1][4] This can be contrasted to the Microsporidium cotti infection of the testes of Taurulus bubalis where a dense microvillus layer is present for improved nutrient absorption.
Other structures may be present inside the infected host cell including vesicles, fat globules and bundles of fibril.
Specific environmental stimulation causes the spore to discharge the polar tube which penetrates the xenoma membrane and provides an exit route for the sporoplasm.
[2] Transmission of such pathogens occurs predominantly via oral administration when in contact or in the vicinity of diseased organisms via the release of infectious spores.
[1] It is widely thought that the first site of entry for many of these parasites is in the gastrointestinal tract where enzymes such as pepsin or even an alkaline pH shift (caused by the mucous layer prominent in this area) induces polar tube discharge.
It was discovered through in situ hybridization that the microsporidia Loma salmonae enters the mucosal epithelium in the intestine and migrates to the lamina propria before arriving at the gills, where it eventually resides, via infecting blood cells.
[8] Microsporidia genera that cause xenomas can therefore be quite diverse and so are characterised more comprehensively into several groups depending on their morphology:[1] Recently fish-infecting microsporidia have been grouped into five classes depending on their molecular traits, a higher level of classification using SSU (small subunit) rDNA analysis.
[13] Whilst xenomas are more highly characteristic of fish, they can be quite extensive in other organisms including crustaceans, insects, oligochaetes and other vertebrates.
[14] 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.
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).
