EMERGENCE OF A Perkinsus-LIKE AGENT IN ANURAN LIVER DURING DIE-OFFS OF LOCAL POPULATIONS: PCR DETECTION AND PHYLOGENETIC CHARACTERIZATION

摘要

Multiple un-explained mass mortality events in free-living larval anurans of the genus Rana have occurred between September 1999 and March 2002. Mortality rates in many instances exceeded 90% of tadpoles, resulting in negligible recruitment that year.However, adult frogs appeared unaffected and successful breeding occurred in subsequent years. A seasonal appearance of the organism was clearly associated with the presence of 1 -4 mo-old tadpoles, with outbreaks beginning December to March in southernstates and April to July in central and northern states. Die-offs occurred in the following states: Florida, Mississippi, Virginia, New Hampshire and Minnesota. Sporadic infections that were not known to be associated with die-offs also occurred in Alaska, Minnesota, Virginia and North Carolina. Infected ranid tadpoles included: wood frogs (Rana sylvatica), Southern leopard frogs (R. sphenocephala), mink frogs (R. septentrionalis), green frogs (R. clamitans), Gopher frogs (R. silvosa) and bullfrogs (R.catesbeiana). Gross pathologic findings are characteristic: mild to massive enlargement of the liver, spleen, pronephroi and mesonephroi; affected organs are homogenously white. Histopathologically and cytologically, these four organs and others have massive infiltrates of spheric, darkly basophilic organisms morphologically reminiscent of primitive protozoa of the newly erected clade, Mesomycetozoa (e.g.,Dermocystidium, Dermosporidium, rosette agent and Ichthyophonus).