HOST GENES, PARASITES AND PARASITIC INFECTIONS

Resistance to infection of mammalian hosts by parasites is under genet ic control at many different levels: between species, between races, b reeds and lines of single species and between individuals. These genet ic effects have been described in many host parasite systems. Here we review the interaction between three elements: host genes, parasites a nd the environment in which parasitic infections develop. Already live stock industries exploit genetic variation between breeds, particularl y for the control of trypanosomiasis and tick infestation in cattle. I n most populations, and to many diseases. resistance is heritable and selective breeding for resistance in commercial livestock species has been successful experimentally. Attempts at utilizing genetic variatio n are placed in the broad context of the coevolution of host and paras ite, the limited knowledge we have of the mode of action Of resistance genes and our ability to use genetic information to predict resistanc e to parasites.