Quasi-energy microbes are lifeforms that live in a plasma streamer.
When introduced into a human they cause great pain with affected areas lighting up with blue flashes. They cause death as the body is invaded with high energy plasma that they carry.
They were discovered when the USS Enterprise-D responded to the stricken vessel USS Yosemite which while conducting an experiment had a container of plasma band explode releasing the microbes. They were responsible for an explosion aboard the ship and the death of a crewman.
During transport betweeen the two ships, Barclay was bitten by one of the microbes and alerted Catain Jean-Luc Picard. Four crewmembers of the Yosemite were discovered floating dematerialized in the transporter buffer. They were trying to cleanse themselves of the microbes, but their human patterns got trapped in the transporter. With the aid of Barclay, however, they were rescued. (TNG: "Realm of Fear")