Control of parasites in natural populations: nematode and virus infections of red grouse

The development of analytical models describing the dynamics of host-parasite interactions have stimulated studies of infections of wild animal populations and indicated possible control techniques. It is apparent that parasites influence the size of the host population and the pattern of population changes. This is illustrated with reference to Lagopus lagopus scoticus. The caecal nematode Trichostrongylus tenuis causes a reduction in the breeding production of grouse sufficient to account for the regular cyclic fluctuations in numbers. Control of T. tenuis has centred around chemotherapy; direct chemotherapy has proved successful but is of no long-term benefit while initial results from indirect chemotherapy, using grit coated with a fat and incorporating an anthelmintic, are encouraging. Louping-ill is a viral infection of sheep and grouse which can cause serious losses to both populations. Grouse cannot sustain the disease in the absence of sheep, which act as a reservoir host, but vaccination of sheep has failed to prevent sheep amplifying the virus to grouse. -from Authors