I saw a movie in which a group of young adults are in the outback or some Australian desert setting and one of the girls become becomes infected and is hostile and feral she kills a kangaroo and then one of the men becomes infected as well. A cave plays a big role in the story and towards the end a giant worm like parasite latches onto another female character. It’s from late 200o’s or 2010’s I saw it on IFC and pretty confident it’s a indie film.
Primal (2010)
http://www.imdb.com/title/tt1438534/?ref_=fn_al_tt_1