Pathogenesis of Aquatic Bird Bornavirus 1 in Poultry
Aquatic bird bornavirus 1 (ABBV-1), a novel orthobornavirus, was first identified in 2009 in waterfowl, associated with neurological disease and non-suppurative inflammation of the nervous system. Since then, ABBV isolates have been identified in at least 12 free-ranging avian species, including those outside the order Anseriformes, suggesting the potential for a broad host range. Epidemiological studies have also shown that ABBV-1 is highly prevalent in certain populations of Canada geese, with seroprevalence over 50 %. Developing an experimental model to study ABBV-1 is integral to furthering our understanding of ABBV-1 pathogenesis in those avian species that are naturally infected by this virus. In addition, the risks the virus poses to the commercial poultry industry is unknown. Therefore, the objectives of this thesis were as follows: Characterize the pathogenicity of ABBV-1 in vivo using 1) Muscovy ducks (Cairina moschata), as a representative waterfowl species, and 2) White Leghorn chickens (Gallus gallus domesticus), as an avian species of importance to the poultry industry. One hundred and sixty two-day-old birds of each species were inoculated with ABBV-1 through one of four routes of administration: intracranial (IC, n = 40), intramuscular (IM, n = 40), oral (PO, n = 40), or sham-inoculated control (CO, n = 40). Ten birds from each inoculation group were euthanized at 1, 4, 8, and 12 weeks post infection (wpi) for tissue collection. The results of this thesis demonstrated that ABBV-1 delivered IC and IM, but not PO, infects both Muscovy ducks and White Leghorn chickens. By 12 wpi, viral RNA was identified in nervous tissues (brain, spinal cord) of both species, and peripheral tissues of ducks (proventriculus, kidney, gonad), as shown by reverse transcription quantitative polymerase chain reaction and immunohistochemistry. Ducks and chickens developed similar microscopic lesions in nervous tissues, typical of natural ABBV-1 infection in waterfowl, but did not show signs of clinical disease. These results suggest Muscovy ducks are a suitable in vivo experimental model for studying ABBV-1 pathogenesis and chickens are susceptible to infection, but further investigation into the development of clinical signs and natural route of transmission are needed.