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Evaluation of the inhibitory effects of gamma irradiation on the viability of helminth eggs
|關鍵字:||小鼠蟯蟲症;Oxyuriasis;γ射線照射;最低有效照射劑量;小鼠蟯蟲;四翼無刺蟯蟲;貓絛蟲;山羊胃腸道線蟲;馬胃腸道線蟲;gamma-ray irradiation;minimal effective irradiation dose;Syphacia obvelata;Aspiculuris tetraptera;Taenia taeniaformis;goat gastrointestinal nematodes;horse gastrointestinal nematodes||出版社:||獸醫學系||摘要:||
本研究分為四部分，第一、為了瞭解小鼠蟯蟲症（Oxyuriasis）感染現況，針對台中市各研究室及寵物店飼養的小鼠進行調查。第二、為了要控制小鼠蟯蟲症，進行使用γ射線照射蟯蟲卵，評估γ射線對蟲卵胚胎化與生存能力的影響。第三、利用γ射線處理貓絛蟲蟲卵，降低貓絛蟲的散播。第四、對於山羊及馬胃腸道線蟲蟲卵，利用γ射線照射，找出能夠抑制蟲卵孵化或殺死寄生蟲蟲卵的最小有效照射劑量(Minimal Effective Dose, MED)，期望能藉由放射線的使用避免家畜的寄生蟲感染。
HeN、ICR，年齡為6~16週，共有230隻。寵物店有5家，共有140隻年齡介於4~12週之混種小鼠。以Scotch膠帶法檢查小鼠蟯蟲（Syphacia obvelata），以浮游法檢查四翼無刺蟯蟲（Aspiculuris tetraptera）。調查結果，230隻實驗小鼠感染小鼠蟯蟲有16隻；感染四翼無刺蟯蟲的小鼠有6隻。140隻市售小鼠感染小鼠蟯蟲有91隻；感染四翼無刺蟯蟲的小鼠有58隻。
將小鼠蟯蟲及四翼無刺蟯蟲的蟲卵以不同劑量的g射線處理。處理後的蟲卵利用口服的人工感染方式餵食無特定病源(SPF)的實驗小鼠或體外培養的方式，並觀察蟲卵的胚胎化率，並用穿透式電子顯微鏡（TEM）觀察γ射線照射過的蟯蟲卵。在體外培養方面，蟯蟲卵以3kGy的劑量照射後仍可觀察到蟲卵胚胎化；在實驗動物方面，蟲卵經γ射線處理後，感染實驗小鼠，分別於感染後第十天（S. obvelata）及第二十二天（A. tetraptera）犧牲，小鼠蟯蟲在照射量超過1kGy，小鼠體內便無感染蟯蟲；四翼無刺蟯蟲則照射量超過3 kGy，小鼠體內才無感染蟯蟲。因此，小鼠蟯蟲及四翼無刺蟯蟲的最小有效照射劑量分別為1kGy及3kGy，即使蟲卵在經過1及2 kGy的照射劑量後蟲卵內有幼蟲存在，但因不具感染力所以無法在小鼠體內發育成功。
This thesis is made up of four parts, (a) Survey of mice in laboratory and pet store in Taichung, (b)Studying on the effect of irradiation to on the infectivity of mice pinworms by evaluating the embryonation and survival of the irradiated eggs, (c) Irradiation to control infectivity of Taenia taeniaeformis, (d) The minimal effective dose (MED) of ionizing radiation that can inhibit or kill the eggs of animal parasite so as to prevent the transmission of the parasites to goat and horse were investigated.
A survey of the pinworms of mice was carried out in laboratory mice kept in 11 laboratories. The species of mice, included BALB/cByJ,C3H/He and ICR.A total of 230 mice age ranging between 6~16 week, were examined by the Scotch tape method for Syphacia sp. and the fecal flotation method for Aspiculuris tetraptera. A total of 140 random outbreed mice of un determined strain from 5 pet stores with age ranging between 4 to 12 weeks were similarly examined. The prevalence of Syphacia obvelata and Aspiculuris tetraptera in mixed mice is higher than in laboratory mice.
Syphacia obvelata and Aspiculuris tetraptera were subjected to gamma-ray irradiation at varying doses. The irradiated eggs were then either orally inoculated into SPF laboratory mice to assay to their viability or were cultured in vitro to determine their embryonation and observation the irradiated eggs with Transmission electron microscope(TEM). S. obvelata and A. tetraptera eggs irradiated with 3kGy were still able to embryonate in vitro. Adult worms of S. obvelata and A. tetraptera were not recovered from mice that were orally inoculated with 1kGy and 3kGy irradiated eggs, at day 10 and 22 postinoculation. Thus, it was considered that the MED of S. obvelata eggs is 1kGy and the MED of A. tetraptera eggs is 3kGy. Despite that the 1 and 2kGy irradiated eggs were able to embryonate after irradiation, they were not viable when assayed in vivo.
Eggs of Taenia taeniaeformis are known to contaminate the feed and bedding of laboratory rat, therefore, Two experiments, one using low and the other high dose irradiation on T. taeniaeformis eggs were carried out. The irradiated T. taeniaeformis eggs were bioassayed in rats and the recovered hepatic larval cysts were enumerated. All the rats inoculated with low dose (0.15 to 0.5kGy) irradiated eggs had T. taeniaeformis larval cysts. In the high dose experiment, significantly more number of larval cysts was recovered from the group of rats that were inoculated with 1kGy irradiated eggs than the lower dose irradiated eggs. Further study is needed to clarify this phenomenon. The MED of T. taeniaeformis eggs was found to be 2kGy.
From the in vitro study using the tile method to hatch the irradiated eggs of H. contortus and T. colubriformis in the goat feces, it was observed that those irradiated with 1.5kGy or above did not hatch at all even when incubated at 30C for 8days. Therefore, the MED for those goat nematodes is considered to be1.5kGy. In contrast, many larvae were found to have hatched in the petri dish that contained the non-irradiated goat feces on the tile. It was thus considered that those nematode eggs were highly susceptible to ionizing irradiation. When horse feces containing the eggs of S. equinus and T. axei that were irradiated with 0.7kGy were cultured in vitro, the larvae of those nematodes were still able to hatch. Therefore, the MED for those horse nematodes is considered to be1kGy.
The information presented above can contribute to a better understanding for the use of nuclear technology in the control of animal parasites of veterinary and medical importance.
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