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During the period of the study no clinical signs of influenza were detected. However, seropositive animals were detected through ELISA in each sampling. At 3 weeks prevalence was 56,2% (68/121) and decreased to 10,4% (12/115) at 6 weeks. Then, and up to 13 weeks, seroprevalence had ups and downs. At 15 weeks, the rest of the seronegative animals had seroconverted. Based on the results of the RT-PCR, sows that eliminated the virus at weeks 3, 4, 7, 13, 15, 17, 20 and 24 were detected, with prevalence that went from 1 to 25%. 4 viral circulation waves were noted: upon weaning (3-4 weeks) and at weeks7, 13 and 20. Curiously, one same animal could eliminate SIV in these different waves of infection.
The results of this study show that SIV can circulate subclinically on endemic farms. The derived maternal antibodies probably persisted during at least 6 weeks, and it is highly probable that very early infections were lessened due to those maternal antibodies. The results also showed the presence of consecutive viral waves that did not propagate the illness, with the exception of the last waves, which suggests the introduction and circulation of a strain that was previously absent in the growth and fattening population.
M. Simon-Grifé, G. E. Martín-Valls, M. J. Vilar, M. Mora, M. Martín, N. Busquets, E. Mateu, J. Casal. Longitudinal study of swine influenza virus infection in a farrow to finish farm. IPVS 2010.
