Abstract
African horse sickness virus (AHSV) is a highly lethal arbovirus of horses, with severe economic impacts associated with the spread and control of the disease. Due to the difficulties of performing experimental studies with horses, this project utilised a mouse model to better study the factors associated with AHSV pathogenicity. The project began by characterising in-depth the pathological features of two different AHSV strains in the interferon-receptor deficient IFNAR-/- mouse model. This study showed that the different clinical outcomes of these AHSV infections were linked with different lesions observed in infected mice. This was corroborated with a multiple-strain infection experiment performed in advance of this project but analysed herein. Finally, this led to investigating how pathological differences and variations in growth kinetics and cellular tropism are linked to genetic differences between viral strains, using next-generation sequencing techniques and a variety of in vitro and ex vivo experiments.
Nucleotide sequencing of the genomes of gene-segment reassortant AHSV strains tested in IFNAR-/- mice indicated that genes encoding the proteins VP1, VP2 and NS4 could play a central role in AHSV pathogenicity. Even though the spleen was commonly targeted by all strains of AHSV in the IFNAR-/- mouse, the severity of spleen pathology differed between AHSV strains that varied in some of these particular proteins. AHSV infection was also frequently associated with pulmonary oedema and pneumonia but neurological lesions were observed only in AHSV-4 infections, again indicating a genetic basis of AHSV pathogenicity. Reassortant viruses that swapped VP1, VP2 and NS4 coding segments showed different tropism and replication capacity in monocyte-macrophage and hepatocyte cell lines and in ex vivo splenocytes.
In conclusion, this IFNAR-/- mouse model can be used to study in detail the molecular determinants of AHSV pathogenicity and would enable further pathogenesis studies in horses with a more targeted approach.