Distribution of antibodies against influenza virus in pigs from farrow-to-finish farms in Minas Gerais state, Brazil

Abstract

Background: Swine influenza virus (SIV) is the cause of an acute respiratory disease that affects swine worldwide. In Brazil, SIV has been identified in pigs since 1978. After the emergence of pandemic H1N1 in 2009 (H1N1pdm09), few studies reported the presence of influenza virus in Brazilian herds.

Objectives: The objective of this study was to evaluate the serological profile for influenza virus in farrow-to-finish pig farms in Minas Gerais state, Brazil.

Methods: Thirty farms with no SIV vaccination history were selected from the four larger pig production areas in Minas Gerais state (Zona da Mata, Triângulo Mineiro/Alto Paranaíba, South/Southwest and the Belo Horizonte metropolitan area). At each farm, blood samples were randomly collected from 20 animals in each production cycle category: breeding animals (sows and gilts), farrowing crate (2-3 weeks), nursery (4-7 weeks), grower pigs (8-14 weeks), and finishing pigs (15-16 weeks), with 100 samples per farm and a total of 3000 animals in this study. The samples were tested for hemagglutination inhibition activity against H1N1 pandemic strain (A/swine/Brazil/11/2009) and H3N2 SIV (A/swine/Iowa/8548-2/98) reference strain.

Results: The percentages of seropositive animals for H1N1pdm09 and H3N2 were 26.23% and 1.57%, respectively, and the percentages of seropositive herds for both viruses were 96.6% and 13.2%, respectively.

Conclusions: The serological profiles differed for both viruses and among the studied areas, suggesting a high variety of virus circulation around the state, as well as the presence of seronegative animals susceptible to influenza infection and, consequently, new respiratory disease outbreaks.

Keywords: Antibodies; Brazil; H3N2; pandemic H1N1; serological profile; swine influenza.

Figure 1

Minas Gerais state map with all sampled areas in this study: 1 = Belo Horizonte Metropolitan area; 2 = Zona da Mata; 3 = South/Southwest; and 4 = Triângulo Mineiro/Alto Paranaíba. N = number of sampled farms in each area.

Figure 2

Serological profiles to H1N1pdm09 virus per area in all studied farms in Minas Gerais state, Brazil. Areas: 1 = Belo Horizonte Metropolitan area; 2 = Zona da Mata; 3 = South/Southwest and 4 = Triângulo Mineiro/Alto Paranaíba. Values are shown as log₂ transformed mean titers with standard error of the means.

Figure 3

Distribution of H1N1pdm09 antibodies in all studied areas, according to the production cycle category. Areas: 1 = Belo Horizonte Metropolitan area; 2 = Zona da Mata; 3 = South/Southwest and 4 = Triângulo Mineiro/Alto Paranaíba.

Figure 4

Distribution of anti-H3N2 antibodies in all seropositve farms, according to production cycle category. 1 = Belo Horizonte Metropolitan area; 2 = Zona da Mata; 3 = South/Southwest and 4 = Triângulo Mineiro/Alto Paranaíba.