leper line, n. — Green’s Dictionary of Slang

leper line n.

[the Western Australia Native Australian Welfare Act (1954), which sought to prevent the spread of leprosy by forcing all sufferers to move to a place south of that parallel]

(Aus., Western) a line running across Western Australia at 20°S.

1958		Canberra Times (ACT) 20 Mar. 9/4: The quarantine provision in the' W.A. Native Welfare Act which prevents natives from crossing the 20th parallel of latitude from north to south. The provision is designed to check the spread of leprosy and the boundary is known as the ‘leper line’.
1966		Baker Aus. Lang. (2nd edn).
1977		F.B. Vickers (ref. to 1955) Stranger no Longer 167: My copy of the Western Australian Native Welfare Act was approved for reprint on 22nd August 1955. . and section 10 in its preamble says: In order that the spread of leprosy within the State may be limited the following provisions shall operate [...] no person shall cause a native to travel from a place north of the boundary line to a place south of the boundary line... The 20th parallel of south latitude was the boundary line, more usually referred to as the Leper line [AND].