Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
contāgĭōsus, a, um, adj. [contagio, II.], contagious (perh. only in Veg.): passio, Veg. Art. Vet. 1, 14, 2: scabies, id. ib. 5, 70, 1.