I've studied zombie lore in some depth, so hopefully I can help to answer this. Since most of the major developments in the "zombie mythology" have occurred in film, my answer will focus on that, but zombies do date back to late-eighteenth century Haitian folklore and the Vodou religion. The infectious disease/virus angle is also not necessarily "new" within zombie lore - while it has been popularized by works such as 28 Days Later (2002) or the Resident Evil video game franchise, also has roots in films like Dawn of the Dead (1978) and Day of the Dead (1985), or even the book I Am Legend (1954). Perhaps most interestingly, much of zombie lore is derived from purported non-fiction sources, rather than pure inventions of storytellers.

I think most historians would identify three main eras of zombies in pop culture, beginning with Haitian Vodou, reaching mainstream popularity with the "living dead," and entering the modern era with the "infected." There have also been other notable sub-genres, such as Frankenstein & science inspired works, like H.P. Lovecraft's Herbert West-Reanimator or Edward L. Cahn's Creature with an Atomic Brain.

The earliest roots of the zombie can be traced back to the late-eighteenth century as part of Haitian folklore and the Vodou religion. Much of what we "know" about the these early "zombis" comes from two journalists, Patick Lefcadio Hearn and William Buehler Sebrook.

Patrick Lefcadio Hearn traveled to the West Indies in 1887, writing two books on his travels. While Hearn claims he "fell under a spell," his quest to find the fabled walking "corps cadavers" yielded mostly second hand accounts. Still, his essay "Country of the Comers-Back" (1889) helped propel zombies into public consciousness. Even more popular than Hearn's work, journalist William Buehler Seabrook's The Magic Island was deeply influential in popularizing the zombie. Based on a 1928 visit to Haiti, Seabrook wrote:

It seemed that while the zombie came from the grave, it was neither a ghost, nor yet a person who had been raised like Lazarus from the dead. The zombie, they say, is a soulless human corpse, still dead, but taken from the grave and endowed by sorcery with a mechanical semblance of life [...] People who have the power to do this go to a fresh grave, dig up the body before it has had time to rot, galvanize it into movement, and then make of it a servant or a slave....

It should be noted that Seabrook was a known sensationalist, and his claims are heavily questioned - he also wrote of vampires, witches, and other monsters - but that didn't stop his book from inspiring a number of incredibly influential works, such as White Zombie (1932) and I Walked with a Zombie (1943). A number of zombie films, often supernatural in nature, would follow, but zombies would eventually lose popularity by the mid-1950s.

Outside of Vodou, zombie films were also shaped by European concepts of the living dead and sentiment towards WWI. The Walking Dead (1936) features the original Frankenstein's monster, Boris Karloff, as a reanimated zombie seeking revenge on his killers, while Abel Gance's J'accuse! (1938) features a war veteran/scientist who raises dead soldiers from all European nations that fought in the previous world war to mount a peace protest.

Perhaps the first work to introduce any sort of apocalyptic disease to the zombie genre would be Richard Matheson's novel I Am Legend, which was subsequently made into the film The Last Man on Earth in 1964. These works are often absent from compendiums on zombie media, perhaps because the monsters in these works were referred to as "vampires" rather than zombies. Still, the book had a profound influence on what is considered the first modern zombie film, George Romero's Night of the Living Dead (1968).

Among other much-copied ideas, Night introduced the concept of a growing horde of flesh-consuming living dead. Before Night, zombie movies would typically feature only a small number of zombies, very often only one or two, whose danger could often be more or less contained. With Night, zombies gained two new qualities: becoming a large growing mass, subservient to none, and having a heavy appetite for flesh. No longer slaves, vengeful spirits, or science experiments, Romero's zombies closely resemble what we know to be a zombie today. Interestingly, Romero himself did not originally consider his monsters to be zombies, calling them "ghouls," and indeed, no Romero film has ever used the word "zombie." While most modern zombie works draw from Night of the Living Dead, such as AMC's TV show The Walking Dead, the original film makes no direct references to the zombie condition being caused by an infectious disease (within the film, scientists speculate that radiation from an returning space probe may be related), but like modern zombie films, any character that dies is likely to return as a zombie.