Evaluation of transmission of swine influenza type A subtype H1N2 virus in seropositive pigs

Young K Choi Department of Clinical and Population Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.
Present address is the Department of Virology and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN 38105.

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Sagar M Goyal Department of Veterinary Diagnostic Medicine, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.

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Han S. Joo Department of Clinical and Population Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.

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Abstract

Objective—To examine clinical signs, virus infection and shedding, and transmission of swine influenza virus (SIV) subtype H1N2 among seropositive pigs.

Animals—Eighteen 3-week-old pigs with maternal antibodies against SIV subtypes H1N1, H3N2, and H1N2.

Procedure—Ten pigs (principal) were inoculated intranasally with subtype H1N2 and 2 groups of contact pigs (n = 4) each were mixed with principal pigs on day 7 (group 1) or 28 (group 2). Two principal pigs each were necropsied on days 4, 14, 21, 28, and 42 days after inoculation. Four pigs in each contact group were necropsied 35 and 14 days after contact. Virus excretion was evaluated after inoculation or contact. Lung lesions and the presence of SIV in various tissues were examined.

Results—Mild coughing and increased rectal temperature were observed in principal pigs but not in contact pigs. Nasal virus shedding was detected in all principal pigs from day 2 for 3 to 5 days, in group 1 pigs from day 2 for 4 to 9 days after contact, and in group 2 pigs from day 4 for 2 to 6 days after contact. Trachea, lung, and lymph node specimens from infected pigs contained virus. Antibody titers against all 3 subtypes in all pigs gradually decreased.

Conclusions and Clinical Relevance—Protection from viral infection and shedding was not observed in pigs with maternal antibodies, but clinical disease did not develop. Vaccination programs and good management practices should be considered for control of SIV subtype H1N2 infection on swine farms. ( Am J Vet Res 2004;65:303–306)

Abstract

Objective—To examine clinical signs, virus infection and shedding, and transmission of swine influenza virus (SIV) subtype H1N2 among seropositive pigs.

Animals—Eighteen 3-week-old pigs with maternal antibodies against SIV subtypes H1N1, H3N2, and H1N2.

Procedure—Ten pigs (principal) were inoculated intranasally with subtype H1N2 and 2 groups of contact pigs (n = 4) each were mixed with principal pigs on day 7 (group 1) or 28 (group 2). Two principal pigs each were necropsied on days 4, 14, 21, 28, and 42 days after inoculation. Four pigs in each contact group were necropsied 35 and 14 days after contact. Virus excretion was evaluated after inoculation or contact. Lung lesions and the presence of SIV in various tissues were examined.

Results—Mild coughing and increased rectal temperature were observed in principal pigs but not in contact pigs. Nasal virus shedding was detected in all principal pigs from day 2 for 3 to 5 days, in group 1 pigs from day 2 for 4 to 9 days after contact, and in group 2 pigs from day 4 for 2 to 6 days after contact. Trachea, lung, and lymph node specimens from infected pigs contained virus. Antibody titers against all 3 subtypes in all pigs gradually decreased.

Conclusions and Clinical Relevance—Protection from viral infection and shedding was not observed in pigs with maternal antibodies, but clinical disease did not develop. Vaccination programs and good management practices should be considered for control of SIV subtype H1N2 infection on swine farms. ( Am J Vet Res 2004;65:303–306)

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