在过去20年里，世界各地不同地方都有关于两栖动物种群数量下降的报道。这些事件被归于不同原因（经常并没有很多证据支持），包括生境损失、气候变化和疾病等。
现在，关于美国明尼苏达州湿地中北方豹蛙（Rana pipiens）的一项案例研究表明，农用化学药品的使用，再加上寄生虫的感染，是造成种群数量下降的一个因素。在这项研究中，研究人员试图找到与这种青蛙身上吸虫幼虫多少相关的因素。这些寄生虫如果很多会使青蛙身体虚弱，引起四肢变形、肾脏损伤、甚至死亡。
在关于吸虫感染的超过240种可靠的预测因素（这些因素从各种不同植物和动物物种的存在到农用化学药品和生境地理因素都包括在内）中，两个因素比较突出：“莠去津”除草剂和 “磷酸盐”化肥。“莠去津”和“磷酸盐”是玉米和高粱生产的主要农用化学药品，它们加在一起可解释吸虫丰度变化的74%。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 455, 1235-1239 (30 October 2008) | doi:10.1038/nature07281
Agrochemicals increase trematode infections in a declining amphibian species
Jason R. Rohr1,2, Anna M. Schotthoefer3, Thomas R. Raffel1,2, Hunter J. Carrick4, Neal Halstead1, Jason T. Hoverman5, Catherine M. Johnson6, Lucinda B. Johnson6, Camilla Lieske3, Marvin D. Piwoni7, Patrick K. Schoff6 & Val R. Beasley3
1 Biology Department, University of South Florida, Tampa, Florida 33620, USA
2 Penn State Center for Infectious Disease Dynamics, Penn State University, University Park, Pennsylvania 16802, USA
3 College of Veterinary Medicine, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802, USA
4 School of Forest Resources, Penn State University, University Park, Pennsylvania 16802, USA
5 Department of Forest, Wildlife and Fisheries, The University of Tennessee, Knoxville, Tennessee 37996-4563, USA
6 Natural Resources Research Institute, University of Minnesota Duluth, Duluth, Minnesota 55811, USA
7 Illinois Waste Management and Research Center, Champaign, Illinois 61820, USA
Global amphibian declines have often been attributed to disease1, 2, but ignorance of the relative importance and mode of action of potential drivers of infection has made it difficult to develop effective remediation. In a field study, here we show that the widely used herbicide, atrazine, was the best predictor (out of more than 240 plausible candidates) of the abundance of larval trematodes (parasitic flatworms) in the declining northern leopard frog Rana pipiens. The effects of atrazine were consistent across trematode taxa. The combination of atrazine and phosphate—principal agrochemicals in global corn and sorghum production—accounted for 74% of the variation in the abundance of these often debilitating larval trematodes (atrazine alone accounted for 51%). Analysis of field data supported a causal mechanism whereby both agrochemicals increase exposure and susceptibility to larval trematodes by augmenting snail intermediate hosts and suppressing amphibian immunity. A mesocosm experiment demonstrated that, relative to control tanks, atrazine tanks had immunosuppressed tadpoles, had significantly more attached algae and snails, and had tadpoles with elevated trematode loads, further supporting a causal relationship between atrazine and elevated trematode infections in amphibians. These results raise concerns about the role of atrazine and phosphate in amphibian declines, and illustrate the value of quantifying the relative importance of several possible drivers of disease risk while determining the mechanisms by which they facilitate disease emergence.
