Dargie J D, Berry C I, Holmes P H, Reid J F, Breeze R, Taylor M G, James E R, Nelson G S
J Helminthol. 1977;51(4):347-57. doi: 10.1017/s0022149x00007707.
We have previously described the characteristics of a relatively non-pathogenic laboratory strain of S. mattheei, attenuation of which was apparently caused by passage in hamsters. We now show that chronic infection with this avirulent strain largely protects sheep from the manifestations of acute schistosomiasis when challenged with a virulent strain of S. mattheei. Four sheep were each infected with 10 000 cercariae of the avirulent strain and, together with four wormfree sheep, challenged 63 weeks later with 10 000 S. mattheei cercariae of a pathogenic strain. Four more sheep acted as uninfected controls. Following challenge, the animals were weighed and bled weekly for PCV and serum protein determinations, and egg counts were carried out fortnightly on faeces taken from the rectum. Red cell and albumin turnover were monitored for two weeks immediately before challenge and for a similar period before necropsy, when the adult worms were recovered by perfusion and tissues sampled for histopathology and egg counting. The unvaccinated sheep developed severe disease 6-12 weeks after exposure characterised by marked anaemia, hypoalbuminaemia and hyper-gamma globulinaemia coinciding with the passage of blood-stained faeces and progressive inappetence. In the vaccinated sheep, there was an even earlier rise in gamma globulins, but the other clinico-pathological changes were generally slower to devleop and much milder in severity. The parasitological data showed that although this was partly due to a reduction in the establishment of the challenge worm population the main factor was probably a reduction in the fecundity of these worms.
我们之前描述过一种相对无致病性的马氏血吸虫实验室菌株的特征，其减毒显然是由在仓鼠体内传代所致。我们现在表明，用这种无毒菌株进行慢性感染，在绵羊受到有毒力的马氏血吸虫菌株攻击时，能很大程度上保护绵羊免受急性血吸虫病症状的影响。四只绵羊每只感染10000条无毒菌株的尾蚴，并在63周后与四只未感染蠕虫的绵羊一起，受到10000条致病菌株的马氏血吸虫尾蚴的攻击。另外四只绵羊作为未感染的对照。攻击后，每周对动物称重并采血以测定红细胞压积和血清蛋白，每两周对从直肠采集的粪便进行虫卵计数。在攻击前两周以及尸检前类似时间段监测红细胞和白蛋白周转率，尸检时通过灌注回收成虫，并采集组织进行组织病理学检查和虫卵计数。未接种疫苗的绵羊在接触后6 - 12周出现严重疾病，其特征为明显贫血、低白蛋白血症和高γ球蛋白血症，同时伴有便血和进行性食欲不振。在接种疫苗的绵羊中，γ球蛋白更早升高，但其他临床病理变化通常发展较慢且严重程度轻得多。寄生虫学数据表明，虽然部分原因是攻击蠕虫群体的定植减少，但主要因素可能是这些蠕虫的繁殖力降低。
