Circuit refers to the bite marks as the Reda Virus. He explains that in
2961 there was an outbreak of this virus. It's not just fatal but it's
also contagious.
Don aka Gluto wasn't happy about Gien/Frax releasing the virus. He
explains he (Gluto) once had the virus but he was cured of it.
Here's Venomark
Here's Gluto's blood