North Korea’s successful launch of an intercontinental ballistic missile on July 4 heightened global fears about the deadly threat of nuclear war.

But nuclear weapons are not the only weapons of mass destruction that experts think North Korea is developing. They warn that the secretive state also possesses chemical weapon stores and may maintain an ongoing biological weapons program as well.

Biological weapons are particularly scary, since they could ignite a global disease pandemic as devastating as nuclear war — a threat Bill Gates wrote about in an op-ed for Business Insider in February.

The status and capabilities of North Korea’s biological weapons program are mysterious, Sonia Ben Ouagrham-Gormley, an associate professor at George Mason University and the author of “Barriers to Bioweapons“, wrote in a recent analysis for the Bulletin of the Atomic Scientists.