Infectious Pancreatic Necrosis: Experimental Induction of a Carrier State in Trout

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Abstract
Infection of 11-mo-old rainbow trout (Salmo gairdneri) with a strain of infectious pancreatic necrosis virus (IPNV) resulted in an inapparent viremia and low levels of anti-IPN-NB antibodies in the serum. Virus was isolated from internal organs and at 110 d after infection reached 103.5 tissue culture infectious doses 50% endpoint (TCID50)/g in the spleen, kidneys, and pyloric ceca, but was 10–100-fold less in other organs. By 150 d after infection, IPNV was virtually undetectable. When 1-mo-old brook trout (Salvelinus fontinalis) were immersed in virus, survivors became carriers for 1 yr. Virus titer reached a maximum of 107 TCID50/g and then declined but remained at levels between 103 and 104 during the 1-yr observation period. Serum samples collected from the brook trout 10 mo after infection contained low levels of anti-IPN-NB antibodies. Thus an IPN carrier state was induced in yearling and juvenile trout and the infection was sustained for a long period. Key words: infectious pancreatic necrosis, inapparent infection, fish viruses, salmonids

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