There was little kids show on PBS called Caillou. It had different lessons. There were always puppets talking about Caillou. There were no humans. This theory has too do with the episode where Caillou got sick.
It's symptoms are the same as the common cold. The doctor and family is confused by it. Thinking it was the common cold. they resort to the normal cold strategy. (Bedrest, liquids, medicine.) After a while the virus mutated to No symptoms. They thought he was cured and resumed Normal activities. The virus then spread to everyone Caillou knew.
Afterwards it mutated causing the CDC to get involved. The research was done and it was a flu strain mixed with rabies. The CDC started giving out face masks after it had become airborne. They banned all contact with animals. They CDC eventually quarantined Caillous town to prevent infection spread. The disease was named "Caillou Flu."
The Virus Spreads
After the towns quarantine the virus mutated again becoming airborne again. It spread to the nearby town which had an airport. By then the CDC had taken measures. But it was in vain. The virus spread to major cities. That was when WHO got involved. The virus mutated to water transmission.
This helped it get across the ocean. The WHO banned all ships and planes from leaving. That was when the virus became deadly. It was placed on The RMS watch list. Then Survivors took it in their own hands. Killing the infected. Soon whole cities where abandoned. At last the virus mutated into Necrosis. That was when the WHO and CDC began on a cure.
The Virus' Origins
The origin was in a zoo in Caillous town. An animal got a rabies strain. Then a zookeeper went to kill the wild animal. After shooting the animal the Zookeeper disposed of the body in an unsanitary way. A dog ate the flesh of the animal. The dog was then adopted. Caillou got bitten by the dog. The virus mutated into a half flu, half rabies strain. It then mutated flu-like symptoms. Thus making Caillou patient Zero and stumping everyone.
The End of Man
The cure attempts failed. Eventually the survivors burned the bodies and governments went under Martial Law. The virus then mutated so it could go into HAZMAT suits. The burning attracted animals which killed the survivors. And the disease made it into Soldiers HAZMAT suits. The human race could no longer go on. The puppets were robots made by scientists to tell the story about Patient Zero and so there would be a race to keep Nuclear power plants from exploding after Humanity was gone.