Browsing by Subject "Prevalence"

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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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    Peanut allergic children residing in Olmsted County, MN: an examination of the prevalence in 2007, incidence rates from 1999-2007 and association between peanut-specific IgE level, tolerance and reaction severity.
    (2011-05) Rinaldi, Maria Carol
    INTRODUCTION Peanut allergy is a significant concern due to increased prevalence over the last few decades, potential severity of a reaction, and the large percentage of children who do not acquire tolerance. This dissertation evaluated rates of diagnosis over time and examined whether peanut-specific IgE level has clinical relevance regarding tolerance and reaction severity. METHODS Data on all children with a peanut allergy diagnosis between 1999-2007 in Olmsted County, MN was collected using the Rochester Epidemiology Project. The first study estimated the prevalence in 2007 and incidence rate of peanut allergy diagnoses from 1999-2007. This study further examined whether the number of peanut allergy diagnoses from 1999-2007 varied by reaction severity. The second study estimated the percentage of children that developed tolerance to peanuts and assessed the association between peanut-specific IgE level and tolerance. The third study evaluated the association between peanut-specific IgE level and reaction severity. RESULTS The 2007 prevalence of peanut allergy was 0.59%. There were statistically significant lower rates of peanut allergy diagnoses among females (82.0%) as compared to males and among children aged 3-17 years (99.9%) as compared to those aged 0-2 years. There was a significant 1.7-fold increase in peanut allergy diagnoses from 3.84 cases per 10,000 children in 1999-2001 to 6.53 per 10,000 children in 2005-2007. There was not a significant difference in the number of children having had mild as compared to moderate/severe reactions over time. In this sample, 16.4% developed tolerance to peanuts. Children with peanut-specific IgE class levels 4-6 as compared to those with levels 1-3 had a significant 91.0% reduced likelihood to develop tolerance after adjustment for number of atopic conditions and a 2.15 non-significant greater odds for a moderate/severe reaction after adjustment for age at diagnosis. CONCLUSION The incidence rate of peanut allergy increased irrespective of severity of first reaction and most children did not acquire tolerance. The majority of those diagnosed with peanut allergy were males and 0-2 years old. Peanut-specific IgE level was not associated with initial reaction severity, but was found to be a useful prognostic tool for tolerance.
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    Prevalence of porcine circovirus Type 2 (PCV2) in the U.S. national swine herd
    (2014-08) Yan, Yang
    Porcine circovirus associated-disease (PCVAD) is a set of different symptoms and diseases caused by PCV2 that causes significant economical lost in swine industry every year. To investigate the prevalence and vaccination status of PCV2 in US swine herd, a total amount of 2989 serum samples from 202 farms of 13 states of United States has been collected and tested serologically using both cap- and rep-specific indirect ELISA. My ELISA data shows PCV2 prevalence in US swine herd is fairly low (13%-27%), and has decreased during the past 5 years.