Rajanna Rangappa, Thimmareddy Pamalapati Mahadevareddy, Sengupta Pinaki Prasad, Siju Susan Jacob, Mamatha Gotakanapura Sanjeevamurthy
Centre for Advanced Faculty Training, Veterinary, College, Hebbal, Bengaluru, Karnataka, India-560024.
ICAR-National Institute of Veterinary Epidemiology and Disease Informatics, Yelahanka, Bengaluru, Karnataka, India-560064.
Acta Parasitol. 2018 Sep 25;63(3):609-616. doi: 10.1515/ap-2018-0070.
Fasciolosis in ruminants in India is caused by the liver fluke Fasciola gigantica. Radix (Lymnaea) spp. are known to carry the infective stages of this parasite. Understanding the seasonal prevalence of F. gigantica infection in the intermediate host is of extreme importance in order to elucidate the transmission dynamics of the parasite. So the present study was designed to determine the bioclimatic distribution of larval stages of F. gigantica in Radix spp. snails as well as to explore the genetic diversity of F. gigantica in three geographical regions (Deccan plateau, Western Ghats and coastal region) of Karnataka. The lymnaeid snails were sampled (n = 2077) for a period of one year (June 2015 to May 2016) at 24 sites. The snails were morphologically identified and the infection status was established through cercarial shedding and nested polymerase chain reaction (PCR) based technique targeting second internal transcribed spacers (ITS-2) of nuclear ribosomal DNA. The sensitivity of PCR (8.2%) for detection of F. gigantica infection within snail is significantly higher than cercarial shedding (4.3%) with an overall prevalence of 5.1%. The prevalence of infection was higher in winter than in the rainy and summer seasons (6.2% instead of 4.6% and 4.3% respectively). Deccan plateau (5.8%) showed a higher prevalence of infection compared to Western Ghats (5.2%) and Coastal region (3.6%). The sequencing ITS-2 region permitted the identification of the parasite as F. gigantica which is having high implication in studying the population genetic structure of the parasite in the country. In conclusion, overall results indicated that Radix spp. snails harboured F. gigantica developmental stages throughout the year and nested PCR was found to be sensitive and specific for detection of F. gigantica infection in snails compared to routine parasitological techniques.
印度反刍动物的片形吸虫病由肝片吸虫巨片形吸虫（Fasciola gigantica）引起。椎实螺属（Lymnaea）的一些物种已知携带这种寄生虫的感染阶段。了解中间宿主中巨片形吸虫感染的季节性流行情况对于阐明该寄生虫的传播动态极为重要。因此，本研究旨在确定巨片形吸虫幼虫阶段在椎实螺属蜗牛中的生物气候分布，并探索卡纳塔克邦三个地理区域（德干高原、西高止山脉和沿海地区）巨片形吸虫的遗传多样性。在24个地点对椎实螺进行了为期一年（2015年6月至2016年5月）的采样（n = 2077）。对蜗牛进行形态学鉴定，并通过尾蚴逸出以及基于巢式聚合酶链反应（PCR）技术靶向核糖体DNA的第二内部转录间隔区（ITS-2）来确定感染状况。PCR检测蜗牛体内巨片形吸虫感染的灵敏度（8.2%）显著高于尾蚴逸出法（4.3%），总体感染率为5.1%。冬季的感染率高于雨季和夏季（分别为6.2%，而雨季和夏季分别为4.6%和4.3%）。德干高原（5.8%）的感染率高于西高止山脉（5.2%）和沿海地区（3.6%）。对ITS-2区域进行测序可将该寄生虫鉴定为巨片形吸虫，这对于研究该国该寄生虫的种群遗传结构具有重要意义。总之，总体结果表明椎实螺属蜗牛全年都携带巨片形吸虫的发育阶段，并且与常规寄生虫学技术相比，巢式PCR在检测蜗牛体内巨片形吸虫感染方面具有灵敏性和特异性。
