ornithosis n an atypical pneumonia caused by a rickettsia microorganism and transmitted to humans from infected birds Usage(s) Another early suspect was ornithosis, a disease transmitted through bird droppings and direct handling of infected birds. They may reward the owner of the hand that feeds them with a dose of ornithosis (better known as psittacosis or parrot fever). Meyer's next project: a medicated feed for table birds, especially turkeys, which are also subject to ornithosis epidemics (PTI, March 26, 1956). Synonym(s) psittacosis parrot fever