Raadsma H W, Kingsford N M, Spithill T W, Piedrafita D
Reprogen, Centre for Advanced Technologies in Animal Genetics and Reproduction, Faculty of Veterinary Science, University of Sydney, Camden, NSW 2570, Australia.
Vet Parasitol. 2007 Feb 28;143(3-4):275-86. doi: 10.1016/j.vetpar.2006.09.008. Epub 2006 Oct 27.
This study reports the early biochemical changes in plasma, comparative host-immune responses and parasite recovery data in Merino sheep during the first 10 weeks of infection with Fasciola gigantica and Fasciola hepatica. One group of sheep were uninfected, four groups of sheep received incremental challenge doses of F. gigantica metacercariae (50, 125, 225 and 400, respectively) and the sixth group was challenged with 250 F. hepatica metacercariae. At 10 weeks post infection (wpi), sheep challenged with F. hepatica showed the greatest fluke recovery (mean 119, range 84-166); a significantly higher biomass of parasites recovered (2.5-fold greater than the highest dose of F. gigantica); and a greater mean % parasite recovery (39.3%, range 27-55%) than any group challenged with F. gigantica. Within the groups dosed with F. gigantica a strong dose-dependent response was observed in both fluke recovery and fluke biomass with increasing dose of metacercariae. The mean % parasite recovery of F. gigantica infected groups 1-5 were 26, 23, 26 and 25%, respectively, suggesting a uniform viability of parasite establishment independent of infection dose. At 6 wpi, elevated levels of plasma GLDH were observed in the F. gigantica infected groups compared to the uninfected sheep (p<0.005) whereas the F. hepatica challenged group had four-fold higher levels of GLDH compared to the F. gigantica infected group (p<0.001). Elevated levels of GGT as an indicator of epithelial damage in the bile duct was only seen in the group challenged with F. hepatica at 10 wpi when it rose from below 100 IU/l to approximately 250 IU/l (p<0.0001) whereas no detectable increase in GGT was observed in any of the groups challenged with F. gigantica. The white blood cell response to F. hepatica infection was biphasic with the initial peak at 4 wpi and a second peak at 9 wpi, corresponding to the period of migration of juvenile fluke in the liver and the time when adult flukes are migrating into the bile duct, respectively. This biphasic response was also evident in the changes in the eosinophil counts and serum haemoglobin levels. There was a trend toward higher parasite-specific IgG2 titres in sheep infected with lower worm burdens, suggesting that higher F. gigantica or F. hepatica burdens suppress IgG2 responses. The findings of this study suggest that, in early infection in a permissive host, F. hepatica appears to be more pathogenic than F. gigantica because of its rapid increase in size and the speed of its progression through the migratory phases of its life cycle.
本研究报告了感染巨片形吸虫和肝片形吸虫的美利奴羊在感染的前10周内血浆中的早期生化变化、宿主免疫反应比较以及寄生虫恢复数据。一组绵羊未感染，四组绵羊分别接受递增剂量的巨片形吸虫囊蚴（分别为50、125、225和400个），第六组接受250个肝片形吸虫囊蚴的攻击。在感染后10周（wpi），感染肝片形吸虫的绵羊显示出最高的吸虫回收率（平均119个，范围84 - 166个）；回收的寄生虫生物量显著更高（比巨片形吸虫最高剂量组高2.5倍）；平均寄生虫回收率更高（39.3%，范围27 - 55%），高于任何感染巨片形吸虫的组。在感染巨片形吸虫的组中，随着囊蚴剂量增加，在吸虫回收率和吸虫生物量方面均观察到强烈的剂量依赖性反应。感染巨片形吸虫的第1 - 5组的平均寄生虫回收率分别为26%、23%、26%和25%，表明寄生虫建立的活力一致，与感染剂量无关。在感染后6周，与未感染绵羊相比，感染巨片形吸虫的组血浆GLDH水平升高（p<0.005），而感染肝片形吸虫的组的GLDH水平比感染巨片形吸虫的组高四倍（p<0.001）。作为胆管上皮损伤指标的GGT水平升高仅在感染肝片形吸虫的组在10 wpi时出现，从低于100 IU/l升至约250 IU/l（p<0.0001），而在任何感染巨片形吸虫的组中均未观察到GGT的可检测增加。对肝片形吸虫感染的白细胞反应呈双相性，初始峰值在4 wpi，第二个峰值在9 wpi，分别对应幼年吸虫在肝脏中迁移的时期和成虫吸虫迁移到胆管的时间。这种双相反应在嗜酸性粒细胞计数和血清血红蛋白水平的变化中也很明显。感染蠕虫负荷较低的绵羊中寄生虫特异性IgG2滴度有升高趋势，表明较高的巨片形吸虫或肝片形吸虫负荷会抑制IgG2反应。本研究结果表明，在易感宿主的早期感染中；肝片形吸虫似乎比巨片形吸虫更具致病性，因为其大小迅速增加以及在其生命周期迁移阶段的进展速度更快。
