Accurate detection of porcine deltacoronavirus infection and the importance of antibody stability in diagnostic specimens

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Yen, Lu
Major Professor
Gimenez-Lirola, Luis
Arruda, Bailey
Baum, David
Zimmerman, Jeffrey
Committee Member
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Veterinary Diagnostic and Production Animal Medicine
Porcine deltacoronavirus (PDCoV) is an enveloped, singled-stranded, positive-sense RNA virus that belongs to the family Coronaviridae, subfamily Coronavirinae and genus Deltacoronavirus. First detected and identified by sequencing during a surveillance in Hong Kong in 2012, it was not until 2014 that PDCoV emerged in the United States associated to cases of acute/watery diarrhea, vomiting, and dehydration in suckling pigs. The non-specific clinical presentation and non-pathognomonic histopathological findings associated to PDCoV infection, and the evidence of co-circulation of different porcine coronaviruses in commercial herds, make the PDCoV differential diagnosis dependent on appropriate laboratory sampling and testing. This thesis consists of two experimental studies focused on PDCoV-specific immunoassay development/evaluation, and the characterization of PDCoV infection in grower pigs under experimental conditions, respectively, and a bibliography review on the impact of antibody stability on veterinary diagnostics. In the absence of commercial vaccines, the detection of PDCoV antibodies indicates current or past infection. Thus, in the second chapter of this thesis, we evaluated the potential of the receptor-binding subunit of the PDCoV spike protein (S1) for IgG antibody detection in an indirect ELISA platform. The assessment of the diagnostic performance of the developed PDCoV S1-based ELISA revealed and high specificity with no serologic cross-reactivity against other porcine coronaviruses commonly circulating in commercial herds. The lack of outbreak reports of PDCoV-associated disease in grower-finisher and adult pigs led us to characterize the dynamic of PDCoV infection in grower pigs. This research study is presented in chapter 3. Under experimental conditions, it was evidenced that PDCoV inoculation of grower pigs resulted in subclinical infection as demonstrated by the detection of active virus replication and shedding in oral fluid and feces, specific PDCoV IgG seroconversion, and increased levels of proinflammatory cytokines in response to PDCoV infection. The forth chapter of this thesis is a comprehensive review on antibody stability in diagnostic specimens and the implications for veterinary diagnostics. Particularly, we deepened our understanding on the general structures of antibodies especially IgG, mechanisms that might lead to antibody instability, including physicochemical and enzymatic processes and the various conditions to storage and preserve the ability of the multiple antibody-containing specimens for diagnostics.