Pfukenyi D M, Mukaratirwa S, Willingham A L, Monrad J
Department of Clinical Veterinary Studies, Faculty of Veterinary Science, University of Zimbabwe, P.O. Box MP167, Mt Pleasant, Harare, Zimbabwe.
Onderstepoort J Vet Res. 2006 Mar;73(1):37-51.
During the period between January 1999 and December 2000, the distribution and seasonal patterns of Fasciola gigantica infections in cattle in the highveld and lowveld communal grazing areas of Zimbabwe were determined through monthly coprological examination. Cattle faecal samples were collected from 12 and nine dipping sites in the highveld and lowveld communal grazing areas respectively. Patterns of distribution and seasonal fluctuations of the intermediate host-snail populations and the climatic factors influencing the distribution were also determined by sampling at monthly intervals for a period of 24 months (November 1998 to October 2000) in six dams and six streams in the highveld and in nine dams in the lowveld communal grazing areas. Each site was sampled for relative snail density and the vegetation cover and type, physical and chemical properties of water, and mean monthly rainfall and temperature were recorded. Aquatic vegetation and grass samples 0-1 m from the edges of the snail habitats were collected monthly to determine the presence or absence of F. gigantica metacercariae. Snails collected at the same time were individually checked for the emergence of larval stages of F. gigantica. A total of 16264 (calves 5418; weaners 5461 and adults 5385) faecal samples were collected during the entire period of the study and 2500 (15.4%) of the samples were positive for F. gigantica eggs. Significantly higher prevalences were found in the highveld compared to the lowveld (P < 0.001), for adult cattle than calves (P < 0.01) and in the wet season over the dry season (P < 0.01). Faecal egg output peaked from August/September to March/April for both years of the study. Lymnaea natalensis, the snail intermediate host of F. gigantica was recorded from the study sites with the highveld having a significantly higher abundance of the snail species than the lowveld (P < 0.01). The snail population was low between December and March and started to increase in April reaching a peak in September/October. The number of juvenile snails peaked between April and August. The mean number of snails collected was negatively correlated with rainfall and positively correlated with temperature. Mean number of snails collected was also positively correlated with Potamogeton plant species and negatively correlated with Cyperus plant species. However, none of the L. natalensis collected from the habitats were found shedding Fasciola cercariae. Metacercariae were found on herbage from the fringes of the snail habitats between February and August for both years, with most of the metacercariae concentrated on herbage 0-1 m from the banks of the habitats. Based on the findings of this study, anthelmintic treatment should be administered in December/January to control chronic and mature fasciolosis. A second treatment should be given in April/May to reduce pasture contamination and subsequently snail infection, as this is the time the snail population starts to build up. To control acute fasciolosis due to the immature liver flukes a third treatment should be given in August. The first application of molluscicides to control the snail intermediate hosts can be done in June the time when the snail is harbouring the parasite and a second application in September in order to kill new generations of infected snails
在1999年1月至2000年12月期间，通过每月进行粪便学检查，确定了津巴布韦高地和低地公共放牧区牛体内巨片形吸虫感染的分布情况和季节模式。分别从高地和低地公共放牧区的12个和9个药浴点采集牛粪便样本。还通过在高地的6座水坝和6条溪流以及低地公共放牧区的9座水坝中，每隔一个月进行为期24个月（1998年11月至2000年10月）的采样，确定了中间宿主蜗牛种群的分布模式和季节波动情况以及影响分布的气候因素。对每个采样点进行相对蜗牛密度的测定，并记录植被覆盖情况和类型、水的物理和化学性质以及月平均降雨量和温度。每月从蜗牛栖息地边缘0 - 1米处采集水生植被和草样，以确定是否存在巨片形吸虫囊蚴。同时采集的蜗牛逐个检查是否有巨片形吸虫幼虫阶段出现。在整个研究期间共采集了16264份粪便样本（犊牛5418份；断奶仔猪5461份和成年牛5385份），其中2500份（15.4%）样本的巨片形吸虫卵呈阳性。与低地相比，高地的感染率显著更高（P < 0.001），成年牛的感染率高于犊牛（P < 0.01），且雨季的感染率高于旱季（P < 0.01）。在研究的两年中，粪便虫卵产量在8月/9月至3月/4月达到峰值。在研究地点记录到了巨片形吸虫的蜗牛中间宿主纳塔尔椎实螺，高地的该蜗牛物种数量显著高于低地（P < 0.01）。蜗牛种群数量在12月至3月间较低，4月开始增加，9月/10月达到峰值。幼螺数量在4月至8月间达到峰值。采集到的蜗牛平均数量与降雨量呈负相关，与温度呈正相关。采集到的蜗牛平均数量也与眼子菜属植物物种呈正相关，与莎草属植物物种呈负相关。然而，从栖息地采集的纳塔尔椎实螺均未发现排出片形吸虫尾蚴。在两年的2月至8月间，在蜗牛栖息地边缘的牧草上发现了囊蚴，大多数囊蚴集中在距离栖息地岸边0 - 1米的牧草上。基于本研究的结果，应在12月/1月进行驱虫治疗，以控制慢性和成熟的片形吸虫病。应在4月/5月进行第二次治疗，以减少牧场污染并随后减少蜗牛感染，因为这是蜗牛种群开始增加的时期。为控制因未成熟肝吸虫引起的急性片形吸虫病，应在8月进行第三次治疗。控制蜗牛中间宿主的杀螺剂首次施用可在6月进行，此时蜗牛携带寄生虫，9月进行第二次施用，以杀死新一代受感染的蜗牛
