观察旋毛虫成囊幼虫的感染性与其发育阶段的关系,18只雌性昆明小鼠经口感染旋毛虫囊包（20个/鼠）,感染后60、100、200、300、400、500 d,分别安乐死3只小鼠,每组取10份肉样（20个囊包/肉样）,分别经口感染10只雌性昆明小鼠。感染后30 d取小鼠完整膈肌,称重后压片镜检,计数囊包。计算每克膈肌虫荷（囊包）。实验结果显示,60 d组囊壁完整,深染层边缘出现透明,幼虫可见;100 d组囊壁完整,深染层边缘外出现透明痕迹,幼虫可见,2个囊包无囊壁和囊内结构,幼虫隐约可见;200 d组囊壁完整,深染层边缘外出现浅色痕迹,幼虫可见,4个囊包无囊壁和囊内结构,幼虫隐约可见或看不到;300 d组囊壁完整,透明带和透明痕迹均可见,幼虫可见,4个囊包无囊壁和囊内结构,幼虫隐约可见或看不到;400 d组多数囊壁完整,透明带和透明痕迹均可见,幼虫可见或隐约可见,12个无囊壁和囊内结构的囊包,囊内幼虫状况分别:可见、隐约可见或看不到;500 d组囊壁不明显或者消失,深染层边缘有透明带,幼虫可见或隐约可见。60~500 d感染组,肌幼虫长度均值分别为:（1 026.6 ± 64.8）、（1 041.1 ± 62.8）、（1 031.5 ± 75.6）、（1 047.9 ± 56.0）、（1 030.5 ± 72.2）、（1 011.2 ± 95.0）μm。60~400 d感染组囊包长度均值分别为:（371.4 ± 69.1）、（309.4 ± 40.3）、（311.9 ± 48.1）、（299.5 ± 43.8）、（294.3 ± 23.4）μm,60 d与100 d组差异有统计学意义（P﹤0.01）。6个实验组小鼠膈肌镜检,均检出幼虫囊包。随着寄生时间的延长,幼虫囊包老化数量和程度加重,感染能力逐渐降低。

To investigate the relationship between the infectivity of encysted larvae and the developmental stage of Trichinella spiralis. Eighteen female Kunming mice were orally infected with 20 encycted larvae each mouse. On days 60, 100, 200, 300, 400 and 500 after infection, three mice in each group were sacrificed by euthanatized, and 10 flesh samples (20 cysts/flesh sample) were used to orally infect 10 female Kunming mice. On day 30 after infection, intact diaphragms were obtained from the mice, weighted, and observed under a microscope to count the cysts. The worm load per gram of diaphragmatic muscle was calculated. In the day 60 group, the walls of cysts were intact, the edge of the deep staining layer was transparent, and larvae were seen. In the day 100 group, the cyst walls were intact, transparency appeared outside the edge of the deep staining layer, and the larvae could be seen; two cysts had no cyst wall or internal structure, with faintly visible larvae. In the day 200 group, the cyst walls were intact, light traces appeared outside the edge of the deep staining layer, and the larvae could be seen; four cysts had no cyst wall or internal structure, with barely visible larvae. In the day 300 group, the cyst walls were intact, the transparent zone and trace seen, and the larvae were visible; four cysts had no cyst wall or internal structure, with faintly visible or invisible larvae. In the day 400 group, most of the cysts had intact walls, the transparent zone and trace were visible, and the larvae were visible or faintly visible; in twelve cysts devoid of wall and cystic structure, the larvae in the cysts were visible, indistinct or invisible. In the day 500 group, the cyst walls were inapparent or even disappeared, with a transparent zone at the edge of the deep staining layer, and the larvae were visible or faintly visible. In the day 60-500 infection group, the average length of diaphragm muscle worm was (1 026.6 ± 64.8), (1 041.1 ± 62.8), (1 031.5 ± 75.6), (1 047.9 ± 56.0), (1 030.5 ± 72.2), and (1 011.2 ± 95.0) μm, respectively. In the day 60-400 infection group, the mean cyst length was (371.4 ± 69.1), (309.4 ± 40.3), (311.9 ± 48.1), (299.5 ± 43.8) and (294.3 ± 23.4) μm respectively, and the difference was statistically significant between day 60 and day 100 groups (P < 0.01). In microscopic examination of all 6 experimental groups, larval cysts were found in diaphragm muscle. This suggested that with prolonged parasitism, increased number and degree of aging of larval cysts would lead to decreasing infectivity.