Epidemic polyarthritis is an outdated term that was formerly used to refer to polyarthritis caused by two mosquito-borne viruses endemic to Australasia:
Barmah Forest virus, which causes Barmah Forest Fever Ross River virus (RRV), which causes Ross River Fever
The term was coined by P. G. Dowling in 1946 to describe an outbreak among Australian troops in North Queensland of a short, mild fever accompanied by polyarthritis, from February to April 1945.
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