TWENTY-FIFTH ANNUAL EASTERN FISH HEALTH WORKSHOP MARCH 10-13, 2000     Myxosporidian Infection Associated With Lesions In Young Menhaden, Brevoortia tyrannus, (Latrobe) In The Pocomoke River     Renate Reimschuessel1 A. Baya2, S. Poynton3, A. S. Kane4, V. Blazer5, J. J. Evans6, M. Kent7, C. Driscoll8   1U.S. Food and Drug Administration, Center for Veterinary Medicine, Office of Research, 8401 Muirkirk Road, Laurel, MD  20708; VA-MD Regional College of Veterinary Medicine, University of Maryland, 8077 Greenmead Drive, College Park, MD 20740; 3Division of Comparative Medicine, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 459, Baltimore, MD. 21205-2196; 4University of Maryland, School of Medicine, Aquatic Pathobiology Center, Department of Pathology, 10 South Pine Street, Baltimore, MD  21201; 5National Fish Health Research Laboratory, U.S. Geological Survey, 1700 Leetown Road, Kearneysville, West Virginia, 25430; 6U.S. Department of Agriculture, Agriculture Research Service, Aquatic Animal Health Research Laboratory, 300 Washington Ave. Chestertown, MD 21620; 7Orgegon State University, Corvallis, Oregon 97331; 8Maryland Department of Natural Resources, Cooperative Oxford Laboratory, 904 South Morris Street, Oxford, MD  21654     Over the past decade, ulcers in Atlantic menhaden have been observed along the east coast of the USA, especially from North Carolina north to Maryland.  These lesions have been attributed to etiologies including bacteria, fungal and recently harmful algal blooms.  In order to better understand the early pathogenesis of these lesions, we examined young of the year menhaden collected from several tributaries of the Chesapeake Bay.  We examined fish from rivers with a history of fish kills and high lesion incidence such as the Pocomoke, and from rivers such as the Transquaking and Nanticoke Rivers, with no known mortalities or lesion incidence.  Fish were collected between May 1999 and September 1999 and processed for routine histopathology.  Seventy nine percent of the juvenile menhaden in the Pocomoke had mature Kudoa spores, presumptive identification Kudoa clupeidae,  located in their muscles, in contrast prevalences in the Transquaking and Nanticoke Rivers were 0 and 30%, respectively.  In most cases the plasmodia containing spores were located within a myomere and caused little to no observable pathological changes.  In addition to the mature Kudoa spores, a highly invasive, plasmodial stage suggestive of a myxozoan was found in the tissues of the Pocomoke menhaden during late May through early July.   These parasites penetrated and surrounded muscle bundles, causing grossly observable raised lesions in 70% of the cases.  In a number of fish, these parasites were also found in the visceral organs, branchial arches and intraocular muscles.  Some of the invasive stage lesions were associated with ulcers and chronic inflammatory infiltrates.  We are currently undertaking studies to investigate the relationship of this unusual proliferative stage with the more typical Kudoa stages.     Return to 25th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page