Between epidemics, viruses can exist in a few different states:
- The virus may persist in a reservoir host.
- The virus may circulate in a population at a low level.
- The virus may be dormant or inactive.
Between epidemics, viruses can exist in a few different states:
The virus may persist in a reservoir host. This is a host in which the virus can replicate and survive without causing disease. For example, the Ebola virus persists in bats, and the SARS-CoV-2 virus (the virus that causes COVID-19) persists in bats and pangolins.
The virus may circulate in a population at a low level. This means that the virus is present in the population, but it is not causing widespread disease. For example, the influenza virus circulates in human populations year-round, but it only causes epidemics in the winter months.
The virus may be dormant or inactive. This means that the virus is not replicating or causing any harm to the host. For example, the varicella-zoster virus (the virus that causes chickenpox and shingles) remains dormant in nerve cells after the initial infection.
The state of a virus between epidemics depends on a number of factors, including the virus itself, the host population, and the environment. For example, viruses that are easily transmitted and that have a long incubation period are more likely to persist in a reservoir host or circulate in a population at a low level. Viruses that are more difficult to transmit and that have a short incubation period are more likely to be dormant or inactive.