What was the origin of the virus?

In the film the where and hows are not well explained other than it was first thought the outbreak started in South Korea however Gerry learns the Israelis had heard about the Indian Army fighting zombies before the Korean outbreak.

In the novel the outbreak started in China.

He killed sixteen Czechoslovakians. Guy was an interior decorator.

I thought the film made it pretty clear that the origins of the virus remained unknown.. Brad Pitt literally says "we don't know what started it" in the final exposition.

The movie never really explained it but I suspect it was generated by the first 5 minutes of bad acting.

The book explained that it had been around since at least Ancient Egypt, the Romans had directives for dealing with outbreaks and a Chinese Emperor displayed a severed zombie head in a jar to Marco Polo.

The movie was apparently originally conceived as a trilogy though after all the production problems I think they've cut back to two movies, but I presume finding the cause would be a theme planned for a later movie.. with the first one focused on surviving and finding a cure or defence.

In the book the outbreak began in the People's Republic of China, which was then covered up. Over time Chinese organ thieves inadvertently caused the virus to spread to South America, Europe, Central Asia, etc. Over time refugees also began to carry the virus, and over time the whole world was suffering an outbreak.

In the film, the origin of the disease changed a few times during development. The very first trailer for WWZ shows Gerry asking Warmbrunn "How would I get into China?" to which Warmbrunn states "China is a black hole." However, because Hollywood depends on the Chinese market, they couldn't risk offending anyone. Instead, they changed it to Russia. Another trailer shows Warmbrunn saying "Russia is a black hole." The entire original ending of the film depicted Gerry flying to Russia after Israel, and then being conscripted into the Russian army to fight the zombies in Moscow.

Eventually, we have the final film which states the first recorded outbreak occurred in India. This makes sense to me, since India is very overpopulated and it would very easily spread. However, the film doesn't go into much more detail other than that. I don't know if the sequel will follow up on this though, since Warmbrunn even tells Gerry to give up searching for "Patient Zero."

Can't be too careful with all those weirdos running around.