From The Collaborative International Dictionary of English v.0.48 [gcide]:
contractable \con*tract"a*ble\ (k[o^]n*tr[a^]kt"[.a]*b'l), adj.
capable of being transmitted by infection; same as
communicable, 1; -- of disease.
Syn: catching, communicable, contagious, transmissible,
transmittable.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) [wn]:
contractable
adj 1: (of disease) capable of being transmitted by infection
[syn: catching, communicable, contagious,
contractable, transmissible, transmittable]