Inhibitory effect of different UV lamps on the infectivity of taeniid eggs.

The expanding distribution of alveolar echinococcosis in Hokkaido, Japan necessitates a search for control measures, particularly for killing Echinococcus eggs; and UV radiation is a potential tool. To determine the effective UV lamp and its optimum duration of exposure to inhibit the infectivity of taeniid eggs, three UV lamps (UVA, UVB and UVC) with peak emissions at different wavelengths were used to irradiate eggs of Taenia taeniaeformis. Irradiation was done in durations of 30, 90, 270, 810, 2,430 and 7,290 s. Infectivity of the irradiated eggs was tested by oral inoculation into rats. The inhibitory effect of the UV lamps at different exposure durations was determined by the reduction in the larval cyst establishment and by the delay of larval development. The UVC lamp (narrow peak at 254 nm) was found to be the most effective lamp at an exposure duration of more than 2,430 s (2,430 mJ/cm2), attaining 100% reduction. Also, shorter exposure durations produced a significant effect on the development of irradiated eggs in a greater percentage of small cysts (> 1 mm) among the metacestodes. Irradiation delayed the development of some cysts, as observed in histopathological sections. UVA and UVB lamps were not able to attain 100% reduction. It is concluded that the UVC lamp can be used as a tool in sterilizing taeniid eggs and is thus a promising method to control echinococcosis, although it may require a higher intensity of exposure.