Effect of Temperature on the Killing of Opisthorchis viverrini Eggs In Vitro.

Contaminated liver fluke egg in the environment has led to the high prevalence of human opisthorchiasis associated with cholangiocarcinoma in Southeast Asia. To find the effective lessening methods of Opisthorchis viverrini eggs in the contaminated environment, we investigated the temperature conditions for killing of these trematode eggs in vitro. Numerous O. viverrini eggs were obtained in the proximal part of uteri of adult worms from experimental hamsters. Mature eggs with miracidium were allocated by experimental groups (2 control: positive and negative and 4 treatment: 50, 60, 70, and 80°C) with 0.85% saline, and treated by the experimental plan. Eggs in each experimental groups were observed under the confocal microscope after stain with Propidium Iodide (PI) to evaluate the effect of temperatures. Eggs in 70 and 80°C groups were all killed after over 10 min heated. Majority of eggs in 60°C (10, 15, and 30 min heated), 70 and 80°C (5 min heated) groups were inactivated. However in 50°C group, below half of eggs were to be killed in all time lapse (10, 15 and 30 min). In order to prevent O. viverrini infection and cholangiocarcinoma, direct treatment of sewage by heating at 70 or 80°C at least 10 min is essential. Therefore, treatment of O. viverrini eggs at a high temperature is a potential method for controlling egg contamination in sewage.

Immunization and challenge shown by hamsters infected with Opisthorchis viverrini following exposure to gamma-irradiated metacercariae of this carcinogenic liver fluke.

Here we report findings to optimize and standardize conditions to attenuate metacercariae of Opisthorchis viverrini by ionizing radiation to elicit protective immune responses to challenge infection. Metacercariae were gamma-irradiated and the ability of irradiated metacercariae to prevent patent infection of challenge metacercariae in hamsters was determined, as well as their ability to induce a host antibody response. Metacercariae irradiated in a dose-dependent manner, with 3, 5, 10, 12, 20, 25 and 50 Gray, were used to infect Syrian golden hamsters by stomach gavage to ascertain the effect of irradiation on ability of the worms to establish infection. In addition, other hamsters were infected with metacercariae irradiated with 20-50 Gray, followed by challenge with intact/wild-type (non-irradiated) metacercariae to determine the protective effect as established by the numbers of adult flukes, eggs of O. viverrini in hamster faeces and anti-O. viverrini antibody titres. Significantly fewer worms were recovered from hamsters immunized with metacercariae irradiated at 20, 25 and 50 Gray than from control hamsters infected with intact metacercariae or 0 Gray, and the worms showed damaged reproductive organs. Faecal egg numbers were decreased significantly in hamsters immunized with 25 and 50 Gray metacercariae of O. viverrini. Moreover, hamsters administered metacercariae that were protected elicited a robust, specific anti-fluke immunoglobulin G response compared to control hamsters, suggesting a role for antibody in protection elicited by radiation-attenuated metacercariae.

Effect of light intensity on Opisthorchis viverrini cercarial shedding levels from Bithynia snails--a preliminary study.

Opisthorchis viverrini requires Bithynia snails as the first intermediate host and cyprinid fish as the second intermediate host. Very low natural infection rates have been reported in Bithynia snails, but very high rates have been found in cyprinid fish in the same endemic region. This study investigated the effect of light intensity, the most important stimulus, on the quantity of O. viverrini cercariae shed from naturally infected Bithynia (Digoniostoma) siamensis goniomphalos snails. Snails were evaluated for cercariae output every hour after exposure to various light intensities for a total period of 7h. The same infected snail was tested under different intensities of light: in the dark, and at 1000, 3000 and 5000 lx. The data showed that under exposure to 1000 and 3000 lx of light, the average percentage and number of cercariae released were higher than that exposed to 5000 lx during the first 2h of the experiment. In contrast, under higher illumination (5000 lx) a longer time (6h) was required to stimulate the peak emergence of cercariae. Darkness was not able to induce O. viverrini cercariae emergence. Among the three intensities of light, exposure at 1000 lx induced the highest average number of released cercariae per snail and the highest percentage of cercarial emergence within the first 2h (125, 54.86%), followed by exposure at 3000 lx (69, 25.58%) and 5000 lx (12, 7.78%). The results suggest that the light intensity of 1000 lx for 2h would be optimal for O. viverrini cercarial shedding from naturally infected B. (D.) siamensis goniomphalos snails.

[Nondrug treatment for opisthorchiasis].

In vitro experimental studies of the antiopisthorchiasis properties of currently available non-drug treatment are ofgreat practical value. The studies demonstrated that the herbal drug ecorsol and the background resonance radiation of the Opisthorchis spectrum exerted an anti-helminthic effect that was evaluated by the marital death and amounted to 83.6 to 96.4%. The experimental studies provided evidence that the background radiation, by using the electromagnetic spectrum of Opisthorchis, had a sufficient helminthocidal effect on mature Opisthorchis felineus in the in vitro experiment, which allows these means to be recommended for the non-drug treatment of chronic opisthorchiasis.

[Use of microwave ovens in the prevention of opisthorchiasis].

The studies were performed to evaluate the impact of microwave radiation on the larval stages of parasites and particularly on the survival of Opisthorchis metacercariae when fish was cooked in domestic microwave ovens. It was found to take less time to free fish and its products from Opisthorchis metacercariae in the microwave oven than that to cook the product completely. The performed experiments have shown that the use of microwave ovens to domestically prepare carps from unfavorable opisthorchiasis water reservoirs is an effective mean of freeing fishes from Opisthorchis metacercariae.

[Decontamination of freshly caught fish infected with Opisthorchis metacercariae by fast electron irradiation]. / Obezzarazhivanie svezhepoimannoi ryby, zarazhennoi metatsekariiami opistorkhid, oblucheniem bystrymi élektronami.

An experiment that decontaminated of opistorchide metacercariae-infected fish is described. Decontamination was accomplished by fast electron radiation on an ILU-6 accelerator. A high larval mortality (about 98-100%) was shown in the biological control invasions of the experiment animals exposed to radiation in different doses from 1.25 up to 2.5 Mrad.