Col. Barnes was the leader of SG-6. After his team went on a reconnaissance mission to P2X-885, he contracted the Prior Plague and became deathly ill.
Col. Barnes led an undercover mission to P2X-885. There they witnessed the Prior convert the population to the Ori religion. One of Barnes’s team, Lt. Fisher was among the crowd as the Prior passed through, and the Prior touched his head while passing as if in blessing.
Unbeknownst to Fisher, this contact made him a carrier for an Ori plague. It was missed in his post-mission exam because it was a previously unknown strain of the disease. Presumably through contact with Fisher, Barnes contracted the plague himself, becoming deathly ill. He and his team were quarantined and treated at the SGC. Later, Dr. Lam reported to Gen. Landry that five SGC personnel died from the disease, but it is unknown if Barnes was one of the casualties.
--Aurora Novarum 10:30, 9 Nov 2005 (EST)