Epidemiology of Influenza A viruses of Swine: Surveillance, Airborne Detection and Dissemination.

摘要

Chapter 2: Swine Influenza Active Surveillance in the United States. Influenza A virus (IAV) in swine continues to be an important swine respiratory agent along with being a source of concern to public health authorities. While veterinary diagnostic laboratories are a valuable source of information with regards to the identification and genetic characterization of newly emerged virus through passive surveillance, there is still a need for additional surveillance programs that can aid in detecting new viruses in a timely manner. An active surveillance program was performed in 32 pig farms throughout the Midwestern United States between June 2009 and December 2011. This active IAV surveillance program provided quality data and increased the understanding of the current situation of circulating viruses in the U.S. pig population.;Chapter 3: Swine influenza virus risk factors in growing pigs. Influenza A virus (IAV) is an important cause of respiratory disease in swine. Understanding the epidemiology of the disease is in its early stages and is needed to develop effective control and prevention strategies. A study was conducted to assess the relationship between the presence of IAV in growing pig farms and farm level risk factors. Positive nasal swabs originated from 23 of the 26 participating farms. Farm type, pig flow and gilt source were associated with the presence of IAV. Environmental temperature and wind speed were associated with the presence of IAV. Overall, this study provides insights into the ecology of IAV which can aid in the development of control and prevention strategies.;Chapter 4: Prevalence and risk factors for H1N1 and H3N2 influenza A virus infections in Minnesota turkey premises. We conducted a cross-sectional study to estimate the seroprevalence of influenza viruses in turkeys and examine factors associated with infection on Minnesota turkey premises. This study suggests that H1N1 and H3N2 influenza virus infections of turkey premises in Minnesota are an uncommon event. The route of influenza virus transmission could not be determined, however, the findings suggest that airborne transmission should be considered in future studies.;Chapter 5: Characterization of the temporal dynamics of airborne influenza A virus detection in acutely infected pigs. Influenza A viruses infect many species including avians, mammals and humans. Aerosol transmission is one route that enables the virus to infect populations. This study explored the relationship between number of infected pigs and the probability of detecting influenza virus RNA in bioaerosols through the course of an acute infection. Positive bioaerosols were consistently detected between 3 and 6 DPC, a time when most pigs were also shedding virus in nasal secretions. Overall, the odds of detecting a positive air sample increased 2.2 times with every additional nasal swab positive pig in the group. In summary, there was a strong relationship between the number of pigs shedding influenza virus in nasal secretions and the detection of bioaerosols during the course of an acute infection in non-immune population.;Chapter 6: Detection of airborne influenza A virus in experimentally infected pigs with maternally derived antibodies. This study assessed whether recently weaned piglets with maternally derived antibodies were able to generate infectious influenza aerosols. Three groups of piglets were assembled based on the vaccination status of the dam. Sows were either non vaccinated (CTRL) or vaccinated with the same (VAC-HOM) strain or a different (VAC-HET) strain than the one used for challenge. This study provides evidence that recently weaned pigs with maternally derived immunity without obvious clinical signs of influenza infection can generate influenza infectious aerosols which is relevant to the transmission and the ecology of influenza virus in pigs.;Chapter 7: Detection of airborne swine influenza A virus in air samples collected inside, outside and downwind from swine barns. Airborne transmission of influenza A virus (IAV) in swine is speculated to be an important route of virus dissemination, but data are scarce. This study attempted to detect airborne IAV by virus isolation and RRT-PCR in air samples under field conditions. The odds of detecting IAV decreased with distance from the farm and greater levels of sunlight intensity. The results from this study prove evidence of the risk of aerosol transmission in pigs under field conditions and perhaps to other species as well. (Abstract shortened by UMI.).