noun
natural host
Biology term for an organism that harbors a pathogen in nature without human intervention.
コウモリは多くのウイルスの自然宿主と考えられている。
Bats are considered natural hosts for many viruses.
宿主 is a general term for 'host' in biology, while 自然宿主 specifically refers to the natural host in an ecosystem.
Compound of 自然 (natural) and 宿主 (host). The exact historical derivation is uncertain, but the term is a modern biological coinage.