The discovery of a gene for a mitochondrial-type chaperone combined with molecular phylogenetic data later implied that microsporidia are atypical fungi that lost mitochondria during evolution.

[4] Genome compaction is reflected by reduced intergenic spacers and by the shortness of most putative proteins relative to their eukaryote orthologues.

[6] Hence, even 20 years after the genome sequence was published, about 50% of the E. cuniculi proteome remains uncharacterized or poorly understood.

The strong host dependence is illustrated by the lack of genes for some biosynthetic pathways and for the tricarboxylic acid cycle.

Because the E. cuniculi genome contains genes related to some mitochondrial functions (for example, Fe-S cluster assembly), it is possible that microsporidia have retained a mitochondrion-derived organelle.

[5] The infective form of microsporidia (E. cuniculi) is a resistant spore which can survive for a long time in the environment.

E. cuniculi has undergone an evolutionary process of genome reduction that has affected all major DNA repair pathways.

[7] First identified in rabbits, E. cuniculi infections have been reported worldwide in over 20 mammalian species, including humans.

Cats appear to be relatively resistant to the organism, although experimental infections in kittens with feline leukemia virus have been described.

[8] E. cuniculi spores are usually shed in urine, but can also be found in the feces and respiratory secretions of infected animals.

[8] Up to 80% of rabbits in the United States and Europe are serologically positive for E. cuniculi, which indicates that they have been exposed to the organism.

[10] Polymerase chain reaction (PCR) has long been established as the standard technique for detection of microsporidia in humans, and attempts to apply this to rabbits are ongoing.

[10] A few studies have shown that albendazole, a benzimidazole drug, can prevent and treat naturally acquired and experimentally induced E. cuniculi infections.

Adverse reactions to benzimidazole drugs, including injury to the small intestine and bone marrow, have been reported in rabbits.