Suspense is a poor word applied to this film, especially if you have ever done true of-roading in crappy weather conditions. Just a reminder, there was no such thing as CGI in 1977.

If the scenes and locations look real, there might be a reason. From the IMDB page:

Besides internal on-set conflicts, William Friedkin said that approximately fifty people “had to leave the film for either injury or gangrene,” as well as food poisoning and malaria. In The Friedkin Connection he added that “almost half the crew went into the hospital or had to be sent home.” Friedkin himself lost fifty pounds (23 kg) and was stricken with malaria, which was diagnosed after the film’s premiere.

There is no such thing as a the pastoral notion of “Rain Forest,” there is only the Jungle and its always trying to kill you.