Shivers

Shivers is a 1975 horror film. The plot description at Wikipedia begins with this:

Dr. Emil Hobbes is conducting unorthodox experiments with parasites for use in transplants. He believes that humanity has become over-rational and lost contact with its flesh and its instincts, so the effects of the alien organism he actually develops is a combination of aphrodisiac and venereal disease. Once implanted, it causes uncontrollable sexual desire in the host.

David Cronenberg directed this, so don't say you weren't warned. It's graphic and disturbing.

trailer:

Senses of Cinema opens with this:

In 1975 David Cronenberg assaulted audiences with Shivers, his third feature, introducing many of the interests and themes that would preoccupy his subsequent films. These themes include an exploration of the relationship between humans and technology, a fascination with the fragility and mutability of the human body, and the radical possibilities of transcending evolution by using science to drastically alter our bodies and minds.

Moria gives it a positive review and says, "what sets Shivers apart from being merely another B exploitation film is the wild metaphors and images that David Cronenberg attaches to the story." HorrorNews.net describes it as "a deeply black comedy set in an upper middle-class apartment building" and says, "What the film gives us, on a small scale, is sexual apocalypse directed with lunatic conviction, and a series of rather revolting variations on the theme of parasitic infection."

Classic-Horror.com opens its review with this:

Although Shivers is not technically David Cronenberg’s first film (he had made some art films previously), it should be considered his debut. Shivers boldly announces the arrival of a creative mind able to concoct horror movies layered with subtext and commentary that don’t forget to entertain at the same time.

Roger Ebert gives it 2 1/2 stars and says, "what's especially effective about "They Came from Within" is that most of the horror is suggested, not shown." Rotten Tomatoes has an 86% critics score.