Metagenomic, Viral and Host Genetic Analyses of Congenital Tremor in Pigs

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A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Biological Sciences, Under the Supervision of Professor Daniel Ciobanu. Lincoln, Nebraska: August, 2020

Copyright 2020 Kylee Marie Sutton

Abstract

The Pestivirus genus contains several viral species having a major impact on the livestock species. While there were only four major pestiviral species for a time, recent metagenomic sequencing approaches identified additional species, such as atypical porcine pestivirus (APPV). Congenital tremor was first identified almost a hundred years ago and since still has an impact on swine health. There are two main types of congenital tremor, type A and B, with type A congenital tremor further subcategorized based on causative agent. Until recently, type A-II congenital tremor did not have a known cause. Recent viral sequencing of affected samples, including our research, revealed APPV to be the predominant viral species in congenital tremor piglets, providing evidence of a causative agent for type A-II congenital tremor.

Various strains of APPV have been identified across the globe. Through sequence comparison, it was found most of the viral APPV genome is not highly conserved. This can lead to misdiagnosis or false-negative results due to variations in the APPV genome sequence when testing of congenital tremor samples is based on qPCR assays. While degenerate primers are an option to combat this, the high degree of variation across the strains and rapid evolution of the viral genome will eventually lead to qPCR assays not recognizing all strains. Whole sequence comparison of full-length APPV genomes demonstrated the 5’ untranslated region (5’UTR) is highly conserved (85%) between 20 worldwide species. This high degree of conservation makes the 5’UTR an ideal candidate region for a universal qPCR assay to detect any strains of APPV.

The role of host genetics in disease susceptibility and severity have been documented for several swine viruses. The swine leukocyte antigen class II complex (SLAII) is involved in the antigen presentation during viral infection. The highly polymorphic DQB1 gene in this region was partially sequenced to provide haplotype profiling to a group of sows subjected to an APPV-based exposure leading to litters with various degrees of congenital tremor. Relationships between DQB1 haplotypes and incidence of congenital tremor and the rate of pre-weaning mortality were investigated. Future more detailed research will need to better quantify the role of host genetics in APPV susceptibility and disease progression.

Advisor: Daniel Ciobanu

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