Swine Influenza in Central and South America

A PEREDA

Dublin

Simposio; 2nd International Symposium on Neglected Influenza Viruses; 2013

International Society for Influenza and other Respiratory Virus Diseases

Influenza A viruses (IAV) are important pathogens responsible for economic losses to the swine industry and represent a constant threat to public health. The clinical presentations of IAV infection in naïve swine population are associated with outbreaks of acute respiratory disease in which morbidity can reach up 100%. In Central and South America, reports of Swine Influenza Virus (SIV) are scarce. Information on SIV activity in Latin America pales in comparison with the wealth of knowledge resulting from SIV surveillance studies in North America, Europe and Asia. The evolutionary and antigenic relationships among SIVs in Central and South America need be determined. In Colombia, the presence of antibodies against SIV has been detected since 1971 in pig operations in Antioquia, showing an overall seroprevalence of 21%. In 2011, a serological survey on 78 herds, from the three major swine rearing areas of Colombia, was carried out. Besides nasal swabs, lungs and bronchial aspirates were processed for virus isolation. Overall serological reactivity by HI test to H1 was 69.0% and H3 49.3%. Fifteen strains belonged 9 herds from the 3 regions evaluated were isolated, 12 of them corresponded to H1N1pdm and 3 to H1N1 classical strains. In Brazil, a great number of cross-sectional serologic studies have indicated the circulation of cH1N1, pdmH1N1 and H3 SIV strains in Brazilian pigs. However, no additional information about the isolated strains was presented. During a 2009-2010, an outbreak of mild respiratory disease in growing pigs and sows detected in a pig herd in Santa Catarina State, Brazil. Immunohistochemistry revealed positive staining in the nuclei of the bronchiolar epithelial cells. Lung tissue from piglets and nasal swabs from sows were positive for influenza A by RT-PCR. An Influenza virus was isolated and the sequences of HA and M genes revealed that the virus was homologue with the pdmH1N1. This was the first report of an outbreak of pdmH1N1 influenza virus in pigs in Brazil. In 2011 and 2012 EMBRAPA analyzed 646 samples of nasal swabs or lung tissue collected from pigs of various ages and raised in commercial herds in Southern Brazil. A total of 111 (17.18%) samples were positive by RT- PCR and 46 (41.44%) influenza viruses were isolated. Complete and partial genomic sequences of 25 SIV were obtained. Based on the sequence analyses 16 influenza viruses showed a high identity (98-100%) with pdmH1N1. Five influenza viruses were closely related to an American H3N8 equine influenza virus and four virus isolates revealed to be a novel reassortant H1N2 influenza virus that had not been detected in pigs in Brazil before the recent influenza outbreak in pigs. The circulation of SIV in pigs in Argentina was initially explored by retrospective serology showing the presence of approximately 41% of positive sera by ELISA. Wholly human H3N2, pH1N1 (Argentina reported the second occurrence of the pH1N1 in pigs in the world), and novel SIVs in pigs derived by independent reassortment events were reported in Argentina. Thereafter clinical, pathological and virological findings have suggested that the infection was widespread among Argentinean pig farms. The SIVs isolated in Argentina are distinguishable from SIVs in North America and represent independent transmission events. At this stage, it is not known whether reassortment among SIVs in Argentina is a common occurrence and/or reflect the exponential growth of the swine industry. In Venezuela, in 2004 a limited serological survey against SIV subtypes H1 and H3 showed 7.9% and 8.2% of positive sera in 7 out of 10 of the farms studied. Further, a cross-sectioned serological study in four farms along a year showed concurrent infection with H1 and H3 SIV subtypes with higher seroprevalence of H3 during the raining season (from May to October), with a cyclic pattern during the study period. In Guatemala a two-year (2010-2011) cross-sectional study for the detection of pH1N1 virus and other SIVs circulating in pig populations was carried out. Influenza virus infection was detected by RRT-PCR (15.8%) and by serological testing (10.2%). A higher proportion of RRT-PCR virus positive samples were observed in herds from commercial farms in comparison to backyard populations. Spatial analyses suggested that positive farms tended to cluster yearly; two clusters were observed in 2010 and one cluster in 2011. These clusters were located 1) on the border between Guatemala and Honduras, 2) around the capital, Guatemala City, and 3) in departments where several influenza viruses have been confirmed in humans. The knowledge of the circulating strains in the region will make it possible to be able to design better diagnostic tests and immunogenicity, due to the very low homology at the amino acidic level of the viral proteins between the different strains of Influenza virus. It is for this reason that it is essential to carry out an epidemiological surveillance of the SIV and recognize their molecular, antigenic and pathogenic characteristics of these viruses. Also it is important to state that instead of the potential direct impact of this disease in terms of public health, it is also important to understand another impact that this disease has in Public Health. There are several infections associated with SIV and an increase in the use of antimicrobial agents to control secondary infections increase the risk of bacteria resistance to various antibiotics and increased residues in pork.