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Epidemiological Aspects of Transmission and Control of Porcine Reproductive and Respiratory Syndrome Virus Infection and Associate Diseases

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dc.contributor.advisor Poljak, Zvonimir
dc.contributor.advisor Dewey, Cate Hien, Le Thanh 2011-12-23T15:04:54Z 2011-12-23T15:04:54Z 2011-12 2011-12-19 2011-07-03
dc.description.abstract This thesis presents studies conducted to investigate an outbreak of porcine high fever disease (PHFD) in a small area of Vietnam, in terms of mortality, morbidity, spatial transmission between herds, and risk factors for the disease. This is a severe disease with very high mortality in all age groups which has been considered to be caused by highly pathogenic porcine reproductive and respiratory syndrome (PRRS) virus strains. The focus of the thesis then shifted; to the investigation of within-herd transmission of PRRS virus (PRRSV) infection in commercial herds typically present in Ontario; to the evaluation of commonly used control strategies; and to the estimation of sensitivity and specificity of the PCR test used in surveillance of PRRSV. During our investigation of a PHFD outbreak, it was found that 33.4% of households were cases, and the mortality in these cases was 24.3%, 22.8%, and 6.7% in sows, suckling-nursery pigs, and finishing pigs, respectively. The spatial spread of the disease in the area was very limited, whereas introduction of pigs into a farm before the outbreak was identified as a risk factor. Moreover, it was also found that raising ducks in proximity to pigs and feeding of water green crop to pigs increased the risk for PHFD. For within-herd dynamics of PRRSV infection, the basic reproductive number (Ro) for PRRSV and duration of detectable maternal antibodies (m) in suckling and nursery pigs was estimated. Ro was found to be high (Ro=9.76 ) and m was short (m=3 weeks). The results of mathematical modeling suggested that it is possible to eliminate PRRSV infection from a herd by using herd closure or mass immunization. However, duration of sow immunity, and efficacy of immunization could play a critical role in this result. Finally, our study found that the sensitivity of tissue PCR is higher than the sensitivity of serum PCR and the likelihood of detecting the virus in tissue was higher in pigs with dyspnea or rough hair coat, but lower in lame pigs. This finding can help to increase the sensitivity of risk-based surveillance programs. en_US
dc.description.sponsorship Ministry of Education and Training of Vietnam, Canada Swine Health Board, Department of Population Medicine of The University of Guelph, NSERC Discovery Grant, Ontario Pork, en_US
dc.language.iso en en_US
dc.publisher University of Guelph en_US
dc.rights Attribution-NonCommercial-NoDerivs 2.5 Canada *
dc.rights.uri *
dc.subject PRRS en_US
dc.subject Swine en_US
dc.subject Modeling en_US
dc.subject Clustering en_US
dc.subject surveillance en_US
dc.title Epidemiological Aspects of Transmission and Control of Porcine Reproductive and Respiratory Syndrome Virus Infection and Associate Diseases en_US
dc.type Thesis en_US Population Medicine en_US Doctor of Philosophy en_US Population Medicine en_US
dcterms.relation Le H, Poljak Z, Deardon R, Dewey CE; Clustering of and Risk Factors for the Porcine High Fever Disease in a Region of Vietnam; Transbound Emerg Dis. 2011 Jul 3. doi: 10.1111/j.1865-1682.2011.01239.x. en_US University of Guelph en_US

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Attribution-NonCommercial-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial-NoDerivs 2.5 Canada