Dynamics of viral hemorrhagic septicemia, viral erythrocytic necrosis and ichthyophoniasis in confined juvenile Pacific herring Clupea pallasii.
Capture of wild, juvenile herring Clupea pallasii from Puget Sound (Washington, USA) and confinement in laboratory tanks resulted in outbreaks of viral hemorrhagic septicemia (VHS), viral erythrocytic necrosis (VEN) and ichthyophoniasis; however, the timing and progression of the 3 diseases differed. The VHS epidemic occurred first, characterized by an initially low infection prevalence that increased quickly with confinement time, peaking at 93 to 98% after confinement for 6 d, then decreasing to negligible levels after 20 d. The VHS outbreak was followed by a VEN epidemic that, within 12 d of confinement, progressed from undetectable levels to 100% infection prevalence with >90% of erythrocytes demonstrating inclusions. The VEN epidemic persisted for 54 d, after which the study was terminated, and was characterized by severe blood dyscrasias including reduction of mean hematocrit from 42 to 6% and replacement of mature erythrocytes with circulating erythroblasts and ghost cells. All fish with ichthyophoniasis at capture died within the first 3 wk of confinement, probably as a result of the multiple stressors associated with capture, transport, confinement, and progression of concomitant viral diseases. The results illustrate the differences in disease ecology and possible synergistic effects of pathogens affecting marine fish and highlight the difficulty in ascribing a single causation to outbreaks of disease among populations of wild fishes.
Hershberger
Paul
P
Western Fisheries Research Center, Marrowstone Marine Field Station United States Geological Survey, Biological Resources Discipline, 616 Marrowstone Point Road, Nordland, Washington 98358, USA. phershberger@usgs.gov
Hart
Alexandra
A
Gregg
Jake
J
Elder
Nancy
N
Winton
James
J
D000818:Animals; D021821:Communicable Diseases, Emerging / Q000469:parasitology / Q000662:veterinary / Q000821:virology; D004912:Erythrocytes / Q000821:virology; D005393:Fish Diseases / Q000453:epidemiology / Q000469:parasitology* / Q000821:virology*; D005399:Fishes; D031941:Hemorrhagic Septicemia, Viral / Q000453:epidemiology / Q000401:mortality / Q000821:virology*; D007181:Inclusion Bodies, Viral / Q000648:ultrastructure*; D046529:Microscopy, Electron, Transmission / Q000662:veterinary; D009336:Necrosis; D011529:Protozoan Infections, Animal / Q000453:epidemiology / Q000469:parasitology* / Q000503:physiopathology; D013047:Specific Pathogen-Free Organisms; D013997:Time Factors; D014771:Virion / Q000302:isolation & purification / Q000472:pathogenicity / Q000648:ultrastructure