Encephalitozoon cuniculi: diagnostic test and methods of inactivation

Encephalitozoon cuniculi is a zoonotic protozoan parasite in the phylum Microspora that has been shown to naturally infect several host species, including humans, rabbits and dogs. Currently, serological diagnosis of infection is made using the immunofluorescense assay (IFA) or enzyme-linked immunosorbent assay (ELISA). Although these methods are sensitive and reliable, there are several drawbacks to both tests. Cross-reactivity between other Encephalitozoon species is common, and specialized equipment is required for IFA and ELISA. Most wildlife species are unable to be tested using these methods, because species-specific antibodies are required. One goal of this work was to develop a new serological test for diagnosing E. cuniculi infection that would be more practical for use in small veterinary and medical clinics. The effectiveness of the agglutination test was examined in CD-1 and C3H/He mice infected with E. cuniculi or one of 2 other Encephalitozoon species. The results indicate that the agglutination test is 86% sensitive and 98% specific for E. cuniculi, with limited cross-reactivity to E. intestinalis. The test is fast and easy to conduct, and requires no specialized equipment or species-specific antibodies.

Recent reports of microsporidial DNA in crop irrigation waters suggest that unpasteurized juice products may be contaminated with E. cuniculi. High pressure processing (HPP) is an effective means of eliminating bacteria and extending the shelf life of products while maintaining the sensory features of food and beverages. The effect of HPP on the in vitro infectivity of E. cuniculi spores was examined. Spores were exposed to between 140 and 550 MPa for 1 min, and then spores were loaded onto cell culture flasks or were kept for examination by transmission electron microscopy (TEM). Spores treated with between 200 and 275 MPa showed reduction in infectivity. Following treatment of 345 MPa or more, spores were unable to infect host cells. No morphologic changes were observed in pressure-treated spores using TEM.

The effect of disinfectants on in vitro infectivity of E. cuniculi spores was also examined. Spores of E. cuniculi were exposed to several dilutions of commercial bleach, HiTor and Roccal, and 70% ethanol for 10 minutes and then loaded onto Hs68 cells. The results of this study showed that all concentrations of disinfectants tested were lethal to E. cuniculi spores. Encephalitozoon cuniculi spores are more sensitive to disinfectants than are coccidian oocysts and other parasite cysts.