The impact of microparasites on wild animal populations.

Abstract

Field data on microparasites usually consists of broad surveys of serological data that have recorded the prevalence of an immune response to the parasite. Limitations with this approach are highlighted with the example of brucellosis in bison and elk. Nevertheless the data available on this system show a clear tenet of microparasite epidemiology; that these parasites have a distinct threshold of host population size for establishment. Complications may arise when the parasite occurs in a range of species or is transmitted by a vector. The virus that causes Louping ill in red grouse is transmitted by a tick and here the dynamics of the disease depend on the ratio of vectors to grouse; the size of the vector population is determined by the abundance of mammalian tick hosts. An understanding and estimation of parasite transmission rates becomes possible once observations can establish who infects whom acquires infection from whom, both within and between species. Successful control measures have shown that microparasites can have a serious impact on the size of the host population but such effects can have consequences for community structure as illustrated by rinderpest in East Africa.