Strategies of virus maintenance in communities

Abstract

Knowledge is rapidly accumulating about how viruses perennate within individuals. By contrast, much less is known about mechanisms facilitating virus maintenance within populations or communities. Even though perennation and maintenance phenomena are often intimately related, there is an understandable tendency for the overt disease to attract more attention than the silent infection that might have been its source. Virological knowledge has developed in depth rather than breadth as a series of largely independent studies with perspectives circumscribed by the properties of the differing target populations. In this context target populations are the primary subjects of investigation in relation to a specific virus. To some extent, the approach is due to the emphasis placed by urban Man on those few viruses (e.g. measles, Paramyxoviridae) for which humans seem the most important natural host (Figure 6.1(a)). However, viruses circulating within only one population seem exceptional. Of the positions which a target population can occupy in relation to the biology of a virus, the most common seems to be one in which it only has a share in the maintenance, other populations grouped under the term ‘wildlife’ being more or less important, as with monkeys vis-à-vis humans in sylvatic yellow fever (Togaviridae) or the potyvirus watermelon mosaic (Adlerz, in Thresh, 1981) which alternates between wild and cultivated (target) cucurbits (Figure 6.1(b)). In many instances the target population is not involved in virus maintenance, e.g. rabies (Rhabdoviridae) and arenavirus in humans (Casals, in Evans, 1976), maize rough dwarf (Reoviridae) having wild grass hosts (Harpaz, 1972) but damaging maize (Figure 6.1(c)).