Host (biology)

In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna. Examples of such interactions include a cell being host to a virus, a bean plant hosting helpful nitrogen-fixing bacteria, and animals as hosts to parasitic worms, e.g. nematodes.

The word "guest" is also (more rarely) used in biology to refer to the organism that lives with the host.

Definitions

A host cell is a living cell in which a virus reproduces.

A primary host or definitive host is a host in which the parasite reaches maturity and, if possible, reproduces sexually.

A reservoir host can harbour a pathogen indefinitely with no ill effects. A single reservoir host may be reinfected several times.

A secondary host or intermediate host is a host that harbors the parasite only for a short transition period, during which (usually) some developmental stage is completed. For trypanosomes, the cause of sleeping sickness, strictly, humans are the secondary host, while the tsetse fly is the primary host, given that it has been shown that reproduction occurs in the insect.Cestodes (tapeworms) and other parasitic flatworms have complex life-cycles, in which specific developmental stages are completed in a sequence of several different hosts.