The Hate Disease by Murray Leinster

The Med Service people hit strange problems as routine: if they weren't weirdos, they weren't tough enough to merit Med Service attention. Now the essence of a weird problem is that it involves a factor nobody ever thought of before ... or the absence of one nobody ever missed ...
Dr. Calhoun and his pet tormal Murgatroyd work for the Interstellar Medical Service making routine public health inspections on far-flung colonial planets.
When they reach Tallien Three they are greeted with a rocket attack by the Paras, a mutated form of human rapidly replacing the "normals". The normals think it's a pandemic of demonic possession but Calhoun has his doubts.
If he can keep from turning into a Para, or being assassinated by them he just might figure this thing out.
The Hate Disease was first published in Analog Science Fact & Fiction August 1963.
Total Running Time (TRT): 2 hours, 1 min.
Murray Leinster (1896-1975) was a pen name of William Fitzgerald Jenkins, an award-winning American writer of science fiction and alternate history. He wrote and published over 1,500 short stories and articles, 14 movie scripts, and hundreds of radio scripts and television plays.