28th ANNUAL EASTERN FISH HEALTH WORKSHOP April 21-25, 2003 Infectious Salmon Anemia Virus:  Injection Challenge And Waterborne Transmission Monitored By Hematology And Polymerase Chain Reaction Assay Philip E. McAllister1, Christine L. Densmore1, and Patricia A. Barbash2 1U.S. Geological Survey, Leetown Science Center, National Fish Health Research Laboratory, 11700 Leetown Road, Kearneysville, WV  25430; 2U.S. Fish and Wildlife Service, Northeast Fisheries Center, Fish Health Section, P.O. Box 155, Lamar, PA  16848 In July 2002, 4-year-old domestic Atlantic salmon (Salmo salar) broodstock were segregated by gender and as control and infectious salmon anemia virus (ISAv) challenge cohorts.  All fish initially tested as unexposed to ISAv by polymerase chain reaction (RT-PCR) assay.  In September 2002, ISAv cohorts received a primary intraperitoneal injection (104 TCID50) followed at 2 weeks by intravenous and intramuscular injections (104 TCID50).  Control cohorts received the same sequence of injections but with phosphate buffered saline.  At 2-4 week sampling intervals blood was collected via caudal venipuncture for RT-PCR testing and assessment of hematological parameters by complete blood count.  At 2 weeks after primary injection, 100% of the ISAv-exposed fish (21/21) tested as ISAv-PCR positive, and the control fish continued to test ISAv-PCR negative.  Mortality in the ISAv-exposed cohorts began 3 weeks post primary injection and continued with acute mortality for 3 weeks (52%; 11/21) and with chronic mortality for an additional 2 months (24%; 5/21).  Beginning at 4 weeks post injection, some ISAv-exposed fish showed sporadic conversion between ISAv-PCR positive and ISAv-PCR negative.  By 4 months post primary injection, all remaining ISAv-exposed fish (5/5) tested as ISAv-PCR negative.  In January 2003, the remaining control and ISAv-exposed cohorts were cohabitated for assessment of potential horizontal transmission.  Within 4 weeks of combining the cohorts, 93% of the control fish (13/14) tested as ISAv-PCR positive, and within 5 weeks, 86% (12/14) of the control fish died.  The surviving original ISAv-exposed fish (5/5) continued to test as ISAv-PCR negative, and by 8 weeks the surviving control fish (2/2) also tested as ISAv-PCR negative. Substantial decreases in hematocrit, erythrocyte count, and total leucocyte counts were observed among the ISAv-exposed fish at 2 weeks after the initial ISAv challenge.  These parameters rebounded at the subsequent 2-week sampling interval, but alterations in lymphocyte morphology were evident.  Similar hematological changes were noted among the control cohorts following cohabitation with the ISAv-exposed fish. Return to 28th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page