Louping ill virus (LIV) is a tick borne disease that causes mortality in red grouse, an economically
important game bird of British uplands. The aim of this thesis is to extend previously published models
of LIV , to consider the potential impact of different management strategies. In addition a new route of
infection and the seasonal biology of both grouse and ticks will be explored.
Grouse chicks are known to eat ticks as part of their diet in the first three weeks of life which
may contribute to virus persistence if chicks consume infected ticks. This novel route of infection is
incorporated in to the model which predicts that ingestion increases the range of host densities for which
the virus is able to persist. The ingestion of ticks by grouse also reduces the tick population so that for
low host densities the ingestion of ticks by grouse reduces the tick population so virus cannot persist.
The model is adapted to take account of the seasonal biology of grouse and ticks. Although the temporal
predictions of the seasonal models show some differences the addition of seasonality does not alter
the model predictions of when LIV is likely to persist at different grouse and deer densities. Consequently
seasonality is felt to be unimportant when considering management strategies.
The treatment of sheep with acaricide in an attempt to reduce the tick population on a grouse moor
is currently being trialled in Scotland. We use a model to predict the likely effect of this strategy at
different deer densities. The number of ticks found attached to sheep varies so we consider the effect
of tick attachment rates as well as acaricide efficacy. Although we predict that acaricide treated sheep
can reduce the tick population and therefore LIV in grouse in some circumstances the treatment is less
effective in the presence of deer.
Consequently we use a model to make theoretical predictions of the effectiveness of acaricide treated
deer as a control strategy for reducing LIV in red grouse. The effect of culling deer on LIV in grouse is
also modelled and contrasted with the effect of acaricide use. It is predicted that acaricide treatment of
deer could be highly effective, particularly if the deer density is first reduced by culling.
Finally we considered the direct treatment of red grouse with acaricide. Female grouse can be given
an acaricidal leg band which protects her directly and indirectly protects her chicks as they acquire some
acaricide whilst brooding. Trials have suggested this can reduce tick burdens for individuals. We use the
model to determine the potential effect that treating individual broods may have on the whole grouse
population. The model predictions suggest that unless acaricide efficacy on chicks is high and long lasting
treating individual broods is unlikely to reduce LIV in the whole population but will still provide some
benefit for the individuals. The effectiveness of treatment is reduced by higher deer densities.
The success of the management strategies considered in this thesis appear to be restricted by the
presence of deer. It may therefore be that a combination of treatments including the treatment of deer
may be of the greatest benefit to the grouse population.