Green’s Dictionary of Slang

1. (Aus.) syphilis.

1945		‘Beaufort’ in Mess Songs & Rhymes of the RAAF 29: He must have been riddled with sypho or gonna.
1951		(con. 1941) E. Lambert Twenty Thousand Thieves 99: The joker who owns this has sypho. D’yer mind?

2. (US gay) a syphilitic.

1972

B. Rodgers Queens’ Vernacular 206: syph-o a syphilitic.