HGE is carried by ticks and infects humans similarly to the bacterium causing Lyme disease. Its symptoms are flu-like, with fevers and chills, nausea, severe headaches, muscular ache and malaise. It does not produce a bull's eye rash. If treatment is delayed more than a few days, the risk of death increases.
HGE occurs about one third as frequently as Lyme disease, and the same tick can carry both diseases. In one hour's walk in the Northeastern USA woods, one might encounter 4 ticks carrying HGE.