Modelling – progress update Stephen Catterall, BioSS 28 th November 2007

Contents Sheep flock model –Refinements JSRV infection model –Progression to clinical disease –Transmission Conclusion

Sheep flock model Status: it has now been implemented in ‘C’ Very fast! Three versions: hill, upland, lowland Refinements: –Lamb mortality modelling –Incorporate variability between farms

JSRV infection dynamics Status: the JSRV infection model has been implemented in ‘C’ However, more data is needed so as to better estimate some of the parameters Assume: –All sheep initially susceptible –Some sheep acquire infection (without being infectious) –At some point later on, the sheep becomes infectious –After some time the sheep then develops clinical symptoms

JSRV infection dynamics S Not infected E Infected Not infectious Not clinical I Infected Infectious Not clinical STANDARD MORTALITY voluntary/involuntary culling CLINICAL removal from flock

JSRV infection dynamics Modes of transmission –Horizontal transmission –Vertical transmission? close contact between the ewe and her lamb –Indirect transmission via the environment?? not very important but cannot be excluded? All three modes of transmission have been implemented within the model

JSRV infection dynamics Simulation of transmission… –When initialising a susceptible sheep, take U from –and compute –set H=0

JSRV infection dynamics At each discrete timestep… –Increment H by –the sheep acquires infection when

Sheep E I R

In summary Sheep flock model –Complete subject to a few refinements –A paper describing the model is being written JSRV infection transmission model –This has been implemented in ‘C’ –Three modes of transmission modelled –‘Estimation’ of key parameters is still required