Classic TV - Tales of Tomorrow - "Plague From Space" (1952)

USAF Colonel Jeffrey Ward's abilities are put to the ultimate test when a Martian spaceship lands at his base. At first glance the craft has only one passenger, but when an infection breaks out it becomes clear that there was more than one Martian on the ship.
https://www.imdb.com/title/tt0717040/?ref_=fn_al_tt_1

This video is in the Public Domain.