Nobody knew where the Scourge came from, only 2 things were known about it.
Mosquitoes carried it and only one out of a million humans were immune to it.

In all of North America only 400 people survived. Luckily one of the survivors was Dr Tachayon, the authority on Chaotic Time Theory.

We used the remnants of society to build his greatest creation The Time Machine.

I was chosen to be mankind’s savior by traveling 150 million years back in time to hit the mosquitoes when they first evolved with the harshest insecticides ever developed and kill them all before they had a chance to become a pest.

The mission was a complete success, I killed them all and returned to the present expecting it to be like it was before the Scourge, only to be seized by the Intelligent Ants that ruled the world.

The ant scientist told me that humans were driven to extinction by the early Tigers, who without having to worry about blood-born viruses checking their numbers used early humans as convenient food source.