Within host-parasite communities, viral co-circulation and co-infections of hosts are the norm, yet studies of significant emerging zoonoses tend to focus on a single parasite species within the host.
In our new, open access paper in Emerging Microbes and Infections, we tested urine samples collected from underneath flying fox roosts for a range of different paramyxoviruses known to exist within Australian flying foxes. By examining evidence for synchrony in virus shedding over time and space and comparing rates of viral co-detection at the sample and roost level, we aimed to assess whether the better understanding of viral community interactions and dynamics can elucidate drivers of viral dynamics and spillover.
We detected up to nine bat paramyxoviruses shed synchronously. While overall viral prevalence is low, multi-viral shedding from flying fox populations is common. Although there were periods where no viruses were detected, shedding infrequently coalesced into an extreme, brief and spatially restricted multi-viral shedding pulse, coinciding with peak spillover of Hendra virus to horses. (The winter of 2011 saw an unprecedented 18 spillovers). These intense shedding pulses are likely driven by complex ecological and epidemiological drivers over multi-year time scales and appear to be important in driving spillover. Yet, they may go unobserved or underestimated with infrequent sampling intervals in surveillance programs.
We hypothesise that Hendra virus spillover risk is linked to habitat loss & climatic events, which result in acute food shortages for flying foxes. This could also drive multi-viral shedding and spillover and so argues for solutions that address ecosystem and flying fox health.
Using Markov Random Fields models, we also detected co-occurrence patterns suggestive of interactions among viruses, such as facilitation and cross-immunity. These interactions within the broader viral community could be influencing the spillover of zoonotic pathogens. For example, Teviot, Hendra and Yeppoon viruses showed now co-association with each other within a sampling session, but within samples, the presence of Teviot virus was strongly co-associated with Hendra, or Yeppoon, but not both. Further research into Teviot virus is warranted.
This video describes these findings and shows some of the work we're doing within our Bat1Health team
group to investigate the links between habitat loss, the ecology & health of flying foxes, & the dynamics & spillover of viruses they host.