A mite genus in the family Dermanyssidae.
- O. bacoti (syn. Bdellonyssus, Liponyssus) bacoti — parasitic in rats and humans, the intermediate host of the filarial nematode of rats, Litomosoides sigmodontis, vector of Yersinia pestis (human plague), murine typhus and Q fever. Called also tropical rat mite.
- O. bursa — parasitizes birds. Called also tropical fowl mite.
- O. sylviarum — a parasite of birds.
