The Collaborative International Dictionary of English v.0.48:

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]

WordNet (r) 3.0 (2006):

contractable
    adj 1: (of disease) capable of being transmitted by infection
           [syn: catching, communicable, contagious,
           contractable, transmissible, transmittable]