Browsing by Subject "Transmission"

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    Epidemiology of influenza A viruses of swine: surveilance, airborne detection and dissemination
    (2012-08) Corzo, Cesar Agustin
    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. Thirty nasal swabs were collected from growing pigs on a monthly basis and tested for IAV by RRT-PCR. During sample collection, data on sample collection date, pig age, pig group respiratory signs, clinical status and vaccination history were recorded. A total of 16,170 nasal swabs from 540 groups of growing pigs were collected from which 746 (4.6 %) nasal swabs and 117 (21.7 %) groups tested positive for IAV, respectively. Throughout the study, IAV was consistently detected in at least one farm except in two months. From the positive groups of pigs, H1N1, H1N2, H3N2, 2009 pandemic H1N1were detected in 18%, 16%, 7.6% and 14.5% of the groups, respectively. In seven groups, H1N2 or H3N2 reassortants containing genes from 2009 pandemic H1N1 were found. There were eight groups in which an H1N2 and the 2009 pandemic H1N1 were identified simultaneously. Groups of pigs were more likely to test positive for IAV during the spring and summer seasons compared to the fall. Age and group respiratory clinical signs were not predictors of group IAV status. 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. Further studies in swine should be conducted to increase our knowledge regarding the characteristics of IAV. 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. Twenty-six pig farms participated in the study from which 30 nasal swabs from growing pigs were collected on a monthly basis for 12 or 24 consecutive months between 2009 and 2011. Nasal swabs were tested for IAV by RRT-PCR. Weather stations were located at every participating farm for monitoring temperature, relative humidity, light intensity, wind speed and wind gusts. Farm level data was obtained through a questionnaire to assess the relationship between the presence of IAV and farm level characteristics. At the individual level, 4.6% of the nasal swabs from growing pigs tested positive for IAV. Of the monthly groups of pigs from which nasal swabs were collected, 20.8% had at least one positive nasal swab. 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 premisesInfluenza virus infections can cause respiratory and systemic disease of variable severity and also result in economic losses for the turkey industry. Several subtypes of influenza can infect turkeys causing diverse clinical signs. Influenza subtypes of swine origin have been diagnosed in turkey premises. However, it is not known how common these infections are nor the likely routes of transmission. 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. Results for influenza diagnostic tests and turkey and pig premises location data were obtained from the Minnesota Poultry Testing Laboratory (MPTL) and the Minnesota Board of Animal Health (MBAH) respectively from January 2007 to September 2008. Diagnostic data from 356 premises were obtained, of which 17 premises tested positive for antibodies to influenza A virus by agar gel immunodiffusion (AGID) assay and were confirmed as either H1N1 or H3N2 influenza viruses by hemagglutination and neuraminidase inhibition assays. Influenza infection status was associated with proximity to pig premises and flock size. The latter had a sparing effect on influenza status. 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. Bioaerosols were collected using a cyclonic collector in two groups of seven week-old pigs that were experimentally infected upon exposure with a contact infected pig (seeder pig). After contact exposure, individual pig nasal swab samples were collected daily and air samples were collected three times per day for eight days. All samples were tested for influenza by RRT-PCR targeting the influenza virus matrix gene. All pigs' nasal swabs became influenza virus RRT-PCR positive upon exposure to the infected seeder pig. Airborne influenza was detected in 58% (25/43) of the air samples collected. Temporal dynamics of influenza virus detection in air samples were in close agreement with the nasal shedding pattern in the infected pigs. First detection of positive bioaerosols occurred 2 days post contact (DPC). 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. Piglets acquired the maternally derived antibodies by directly suckling colostrum from their respective dams. At weaning, pigs were challenged with influenza virus by direct contact with an infected pig (seeder pig) and clinical signs were evaluated. Air samples, collected using a liquid cyclonic air collector, and individual nasal swabs were collected daily for 10 days from each group and tested by matrix real-time reverse transcriptase polymerase chain reaction (RRT-PCR) assay. Virus isolation and titration were attempted for air samples on Madin-Darby canine kidney (MDCK) cells. All individual pigs from both VAC-HET and CTRL groups tested positive during the study but only one pig in the VAC-HOM group was positive by nasal swab RRT-PCR. Influenza virus could not be detected or isolated from air samples from the VAC-HOM group. Influenza A virus was isolated from 3.2% and 6.4% air samples from both the VAC-HET and CTRL groups, respectively. Positive RRT-PCR air samples were only detected in VAC-HET and CTRL groups on day 7 post-exposure. Overall, 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. This was accomplished by collecting air samples from four acutely infected pig farms and locating air samplers inside the barns, at the external exhaust fans and downwind from the farms and at distances up to 2.1 km. Weather data was also collected to explore the relationship between detection of IAV and temperature, relative humidity and sunlight intensity. IAV was detected in air samples collected in all the farms included in the study. On average, 96% and 85% of the air samples collected inside and at the exhaust fans from positive farms tested positive through RRT-PCR, respectively. Isolation of IAV was possible from air samples collected inside the barn at two of the farms and in one farm from the exhausted air. Influenza virus RNA was detected in air samples collected between 1.5 and 2.1 Km away from the farms. 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.
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    Influenza In Pigs Prior To Weaning: Sampling Strategies, Transmission Pathways And Approaches To Reduce Prevalence
    (2020-01) Garrido Mantilla, Jorge Eduardo
    Influenza in pigs prior to weaning: sampling strategies, transmission pathways and approaches to reduce prevalence General abstract Influenza is an important disease of swine and it represents a threat to public health because it is caused by influenza A virus (IAV), a zoonotic virus with pandemic potential. One of the objectives that producers and veterinarians have is to control influenza in breed-to-wean (BTW) farms by weaning IAV negative pigs. Pigs prior to weaning play an important role in influenza epidemiology because they can maintain endemic infections in BTW farms and they can disseminate IAV to other farms and regions at weaning. Unfortunately, there is limited information regarding the transmission pathways that lead to piglet infections, nor it is known what effect specific pig-rearing practices and farm management procedures may have on these pathways. To properly detect, isolate and characterize IAV genetically and antigenically, it is necessary to have sampling approaches that accurately define disease status yet are cost-effective to conduct. However, IAV detection and isolation can be challenging in endemic situations. Endemicity and transmission of IAV in pig populations can be affected by certain management practices that are necessary in production and do not allow IAV control. Even though, control of influenza is difficult, it is possible. Vaccination is one of the most common strategies to control influenza transmission and sow vaccination can help to reduce IAV prevalence in piglets. However, the diversity of IAV found in farms requires the use of vaccines that antigenically match the wild-type virus circulating in the pigs in order to provide good cross-protection against the field strains. In an effort to increase vaccine efficacy, custom-made vaccines that include viral strains identified in farms are used to help to control influenza in BTW farms. However, despite the widespread use of custom-made vaccines, there is limited data on the long term effectiveness of using custom-made vaccines in farms. Finally, in this thesis, I aimed to address some of the questions that are central to the transmission and control of IAV in BTW farms and reduce the prevalence of IAV in piglets at weaning. Specifically, I aimed to: 1) identify the best sampling strategy to detect and isolate IAV in weaned and growing pigs, 2) determine the role of nurse sows in the transmission and perpetuation of IAV in pigs prior to weaning, and 3) assess the impact of custom-made vaccines in reducing IAV prevalence in an integrated swine production system over time. The results obtained during my studies determined that IAV detection rates are higher when group and environmental sampling strategies are used compared to samples collected from individual pigs. Nevertheless, individual samples may still be needed to obtain a viral isolate or perform genetic sequencing and virus characterization. As part of my work, I developed the udder skin wipe technique to detect IAV from lactating sows and isolate IAV from litters prior to weaning. Furthermore, I identified that management practices such as the use of nurse sows can transmit IAV between litters thereby perpetuating IAV infection in pigs prior to weaning. Finally, our multi-year evaluations of custom-vaccine usage on BTW farms demonstrated that on-going surveillance and characterization of IAV isolates facilitate vaccine updates with custom-made epidemiologically-relevant strains. In addition to selecting epidemiologically-relevant strains, the strain selection criteria should also include the identification of strains with similar HA antigenic properties, e.g. those with an overall HA protein identity of 95% or more and having identical or nearly identical amino acid motifs. Once selected, these strains can be included in the updated vaccines used to immunize sows and reduce IAV prevalence in their pigs at weaning. The findings on my thesis contribute to the understanding of IAV transmission in pigs before weaning and point to specific strategies to improve surveillance and disease control. Nevertheless, more studies are necessary to elucidate strategies to limit IAV infections and transmission in BTW farms.
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    Transmission and control of influenza virus in pig populations
    (2013-09) Allerson, Matthew William
    Influenza A virus (IAV) is a common cause of respiratory disease in pigs and has been detected in pigs in most pig producing regions of the world. Influenza A viruses are able to infect many different animal species, including pigs, humans, and birds. In addition, influenza A viruses may be transmitted between pigs and other species, including humans. Following the first clinical description of influenza virus infection in pigs in the United States in 1918, research targeting influenza A viruses in pigs and other animal species has intensified quite rapidly. At the same time, control of influenza in swine farms has become increasingly challenging as there are many diverse influenza virus lineages present in the United States. Influenza control is further hindered by the relatively small amount of information assessing influenza virus transmission and within herd infection dynamics as compared to other research disciplines. This thesis aimed to 1) describe within herd influenza virus infection dynamics and temporal patterns of infection in breeding and grow-finish herds, 2) assess the prevalence and temporal patterns of influenza virus infection in weaning-age pigs on commercial swine breeding herds, 3) evaluate influenza virus transmission via indirect routes, and 4) determine the impact of vaccination and maternally derived immunity on influenza virus transmission in weaning-age pigs. The findings of this thesis have advanced the understanding of influenza virus transmission and epidemiology in swine. Researchers, veterinarians and swine producers may utilize this information to investigate influenza virus infections within herds and to help mitigate influenza virus infections.