Acute and persistent viral life strategies and their relationship to emerging diseases.

T r q a r n t e p d h h i o t e s Most virologists would accept the concept that particular viruses often appear to have either acute or persistent patterns of host infection. The polyomaviruses of mammals, for example, uniformly establish persistent infections of a specific host. In contrast, it has recently become clear that avian polyomaviruses infect a broad array of bird species in an acute pattern (Lafferty et al., 1999; Phalen et al., 1999; Johne and Muller, 1998). In this eview, we develop the proposal that these two infection atterns define two life strategies of viruses with distinct volutionary ecologies and consider the consequences n viral fitness and the ecological and evolutionary relaionships. We suggest that persistent host-specific viral gents are the origin of emerging acute epidemic disase following adaptation of that virus to new host pecies. The concept of life strategy for a species was first pplied in an island biogeographical context where it ppeared that specific organisms were better adapted ither for initial habitat colonization (r-selected) or for ong-term population equilibria (K-selected) (MacArthur nd Wilson, 1967). We have previously considered if pecific viruses might also exist with distinct life strateies. However, since various acute viruses can be both a irgin soil epidemic (r-selected) and a childhood infecion at equilibrium in the population (K-selected), these ife strategies cannot be applied to individual viral speies (Villarreal, 1999). Yet viruses do appear to have istinct patterns of acute and persistent host infection. iral persistence has been considered with respect to ources of epidemic disease (Mahy, 1985; Domingo et l., 1998; Holland, 1996; Oldstone, 1998a). However, the erm persistence can often include persistence of viral gents in host populations or in the environment [better ermed viral durability (Cooper, 1985)]. To elucidate a