Disentangling synergistic disease dynamics : implications for the 9 viral biocontrol of rabbits 10 11

33 1. European rabbits ( Oryctolagus cuniculus) have been exposed to rabbit haemorrhagic 34 disease virus (RHDV) and myxoma virus (MYX V) in their native and invasive ranges for 35 decades. Yet, the long-term effects of these viruses on rabbit population dynamics r emain 36 poorly understood. 37 2. In this context, we analysed 17 years of detailed capture -mark-recapture data (2000 – 38 2016) from Turretfield, South Australia, using a probabilistic state -space hierarchical 39 modelling framework to estimate rabbit survival and epidemiological dynamics. 40 3. While RHDV infection and disease-induced death were most prominent during annual 41 epidemics in winter and spring, we found evidence for continuous infection of susceptible 42 individuals with RHDV throughout the year. RHDVsusceptible rabbits had , on average, 43 25% lower monthly survival rates compared to immune individuals, while the average 44 monthly force of infection in winter and spring was ~ 38%. These combined to result in an 45 average infection -induced mortality rate of 69% in winter and spring. 46 4. Individuals susceptible to MYXV and immune to RHDV had similar survival probabilit ies 47 to those having surviv ed infections from both viruses, whereas individuals susceptible to both 48 RHDV and MYXV had higher survival probabilities than those susceptible to RHD V and 49 immune to MYXV. This suggests that MYXV may reduce the future survival rates of 50 individuals that endure initial MYXV infection. 51 5. There was no evidence for long-term changes in disease -induced mortality and infection 52 rates for either RHDV or MYXV. 53 6. We conclude that continuous, year-round virus perpetuation (and perhaps heterogeneity in 54 modes of transmission and infectious doses during and after epidemics) acts to reduce the 55 efficiency of RHDV and MYXV as biocontrol agents of rabbits in their invasive range. 56 However, if virulence can be maintained as relatively constant through time, RHDV and 57 MYXV will likely continue realising strong benefits as biocontrol agents. 58 59 A u th o r M a n u s c ri p t