Evaluation of transmission of swine influenza type A subtype H1N2 virus in seropositive pigs.
OBJECTIVE
To examine clinical signs, virus infection and shedding, and transmission of swine influenza virus (SIV) subtype H1N2 among seropositive pigs.


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


METHODS
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
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.
Choi
Young K
YK
Department of Clinical and Population Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108, USA.
Goyal
Sagar M
SM
Joo
Han S
HS
D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D001831:Body Temperature; D009980:Influenza A virus; D009976:Orthomyxoviridae Infections / Q000635:transmission* / Q000662:veterinary*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D034421:Sus scrofa; D013553:Swine Diseases / Q000821:virology*
D000914:Antibodies, Viral