Taylor M G, James E R, Nelson G S, Bickle Q, Dunne D W, Dobinson A R, Dargie J D, Berry C I, Hussein M F
J Helminthol. 1977;51(4):337-45. doi: 10.1017/s0022149x00007690.
Border Leicester X Suffolk sheep infected with a strain of S. mattheei maintained in hamsters do not develop the same pathological changes as Romney Marsh sheep infected with the same strain of parasite before hamster passage. To determine the cause of this reduced pathogenicity, five Romney Marsh sheep were each infected with 10 000 cercariae of the hamster-passaged parasite and five with 10 000 cercariae of a S. mattheei strain from Onderstepoort, South Africa, passaged exclusively through sheep. Striking pathological and parasitological differences were found between the two strains. Infection with the "sheep" strain was lethal, whereas infection with the "hamster" strain produced little evidence of clinical disease. By 13 weeks post-infection the mean body weight of the sheep infected with the sheep strain had declined by 15% compared with both the uninfected controls and the sheep infected with the hamster strain, and the mean PCV was lowered to 20% in the sheep strain infected animals. Egg production began at seven weeks with the sheep strain, faecal counts rising to more than 300 e.p.g., whereas only two of the sheep infected with the hamster strain passed eggs in the faeces (at nine weeks) and the maximum egg count was 50 e.p.g. Twice as many adult worms of the sheep strain were recovered, and, although the number of eggs found in the tissues "per worm pair" was not significantly different, overall egg production was higher for the sheep strain; also more of the sheep strain eggs were deposited in the intestines. Similar parasite differences were seen in a supplementary study in mice and it seemed that "attenuation" of the parasite had occurred, presumably due to its maintenance in hamsters. Histopathological observations and faecal egg counts both indicated an inability of hamster strain eggs to penetrate the intestinal lumen; this was probably important in reducing the pathogenicity of the hamster strain.
感染了在仓鼠体内传代保存的马氏血吸虫菌株的边区莱斯特×萨福克绵羊，与在仓鼠传代前感染相同寄生虫菌株的罗姆尼沼泽绵羊相比，不会出现相同的病理变化。为了确定这种致病性降低的原因，五只罗姆尼沼泽绵羊分别感染了10000条经仓鼠传代的寄生虫尾蚴，另外五只感染了来自南非翁德斯特普特、仅在绵羊体内传代的马氏血吸虫菌株的10000条尾蚴。在这两种菌株之间发现了显著的病理和寄生虫学差异。感染“绵羊”菌株是致命的，而感染“仓鼠”菌株几乎没有临床疾病的迹象。感染后13周，感染绵羊菌株的绵羊平均体重与未感染对照组和感染仓鼠菌株的绵羊相比下降了15%，感染绵羊菌株的动物平均红细胞压积降至20%。感染绵羊菌株的绵羊在七周开始产卵，粪便虫卵计数上升到超过300个虫卵/克，而感染仓鼠菌株的绵羊只有两只在粪便中排出虫卵（在九周时），最大虫卵计数为50个虫卵/克。回收的绵羊菌株成虫数量是两倍，尽管在组织中“每对虫体”发现的虫卵数量没有显著差异，但绵羊菌株的总体产卵量更高；而且绵羊菌株的虫卵更多地沉积在肠道中。在一项对小鼠的补充研究中也观察到了类似的寄生虫差异，似乎寄生虫发生了“减毒”，推测是由于其在仓鼠体内传代所致。组织病理学观察和粪便虫卵计数均表明仓鼠菌株的虫卵无法穿透肠腔；这可能对降低仓鼠菌株的致病性很重要。
