Field validation of phylodynamic analytical methods for inference on
epidemiological processes in wildlife
Abstract
Amongst newly developed approaches to analyse molecular data,
phylodynamic models are receiving much attention because of their
potential to reveal changes to viral populations over short periods.
This knowledge can be very important for understanding disease impacts.
However, their accuracy needs to be fully understood, especially in
relation to wildlife disease epidemiology, where sampling and prior
knowledge may be limited. The release of the rabbit haemorrhagic disease
virus (RHDV) as biological control in naïve rabbit populations in
Australia in 1996 provides a unique dataset with which to validate
phylodynamic models. By comparing the results obtained for RHDV1 with
our current understanding of the RHDV epidemiology in Australia, we
evaluated the performances of these recently developed models. In line
with our expectations, coalescent analyses detected a sharp increase in
the virus trajectory in the first few months after the virus release,
followed by a more gradual increase. The phylodynamic analyses with a
birth-death tree prior generated effective reproductive number estimates
(the average number of secondary infections per each infectious case,
Re) larger than one for most of the epochs considered. However, the
possible range of the initial Re included estimates lower than one
despite the known rapid spread of RHDV1 in Australia. Furthermore, the
analyses that took into account the geographical structuring failed to
converge. We argue that the difficulties that we encountered most likely
stem from the fact that the samples available from 1996 to 2014 were too
sparse with respect to geographic and within outbreak coverage to
adequately infer some of the model parameters. In general, while these
Bayesian analyses proved to be greatly informative in some regards, we
caution that their interpretation may not be straight forward and
recommend further research in evaluating the robustness of these models
to assumption violations and sensitivity to sampling regimes.