Venomous (2001)

​Venomous is a 2001 American direct-to-video disaster horror film directed by Fred Olen Ray, credited as Ed Raymond, and starring Treat Williams, Mary Page Keller and Hannes Jaenicke

In 1991, a group of Iraqi commandos penetrate a secret American government lab, releasing genetically modified rattlesnakes. Over the following years, the snakes breed and multiply. In the present day, an earthquake drives them from the underground to the surface, and the snakes infect whoever they bite with a fatal virus. A small-town doctor tries to correct the situation, but the government wants to hide the traces of its wrongdoings. At the end of the movie, the Snake's lair is located and destroyed by an explosion, killing apparently all vipers. But the last scene shows a viper who survived.