Pathogenesis of aquatic bird bornavirus 1 in waterfowl
Aquatic bird bornavirus 1 (ABBV-1) is a neurotropic virus in the Mononegavirales order that causes persistent infection in the nervous system of wild waterfowl. This virus has a high prevalence in certain populations of wild Canada geese (Branta canadensis) and swans from North America. Experimentally, chickens (Gallus gallus domesticus) and Muscovy ducks (Cairina moschata) have been shown to be permissive to ABBV-1 infection. Therefore, the objectives of this thesis were to evaluate whether Pekin ducks (Anas platyrhynchos domesticus), a common domestic waterfowl species, and Canada geese (Branta canadensis), a possible reservoir, are susceptible to ABBV-1 infection and associated disease. Two-day-old Pekin ducks (n, 121) were inoculated with ABBV-1 through the intracranial (IC; n, 32), intramuscular (IM; n, 30), or choanal (CH; n, 30) routes, and one-week-old, Canada geese (n, 65) were inoculated with ABBV-1 through the IM (n, 23) or cloacal (CL; n, 21) routes. Control birds (CO; 29 ducks and 21 geese) were sham inoculated. For the goose trial, 6 uninoculated birds were added to each group to test transmission. Birds were kept up to 21 (ducks) and 18 (geese) weeks postinfection. At specific time points, select birds from each group were euthanized for necropsy and tissue sampling. Duck eggs were opportunistically collected, and embryos screened for ABBV-1 RNA. Results showed that ABBV-1 delivered parenterally yielded high infection rates (> 43.4 %), while mucosal inoculations were inefficient. Viral RNA was identified by reverse transcription quantitative polymerase chain reaction and immunohistochemistry in the brain, spinal cord, and viscera (proventriculus, kidney, gonads) of both species. While numerous ducks and geese developed mononuclear encephalomyelitis, only a minority of ducks (8.9 %) developed clinical signs. Shedding of viral RNA was frequent in ducks, but almost none in geese. Vertical or horizontal transmission was not detected. These results indicate that Pekin ducks are highly permissive to ABBV-1 infection and partly susceptible to associated disease. While Canada geese became infected, shedding was limited and horizontal transmission did not occur, which is in contrast with a possible role as reservoir. Further studies are needed to better understand transmission pathways and disease development of ABBV-1 in waterfowl.