It is often claimed in popular books and websites that Gregory's condemnation of heretics worshipping Satan in the form of a black cat in his bull Vox in Rama led to a massacre of cats across Europe. However, there is no evidence of any such massacre and no mention of it in any actual sources from the period. It is usually also claimed that this supposed "cat massacre" caused the Black Death a century after Gregory's time, because the plague was spread by rats who were unchecked in Europe due to the decline of cat numbers. While this makes for a good story, it does not square with the evidence. The Black Death did not start in Europe and did not just devastate Catholic territories - it began in central Asia and spread west, devastating large swathes of central Asia, Asia Minor and the Middle East before hitting Europe. It makes no sense that an (alleged) western European massacre of cats could "cause" a pandemic that began well outside of Catholic Europe and had already killed millions across Eurasia. This story is a myth perpetuated, without evidence or references, by popular unscholarly works.
The wikipedia portion misses two points. The cat massacre didn't CAUSE the black death...it just made it worse. Nobody is claiming it started in Europe. It migrated to europe from asia. Imagine the cats are the worlds immune system, and it was weakened, so the attack was worse.
Also, your source is an article about the pope, probably written by the church, so it's not really an unbiased source either. I'd like to fine some true phd level studies relating to cats and diseases/plague/rat population etc. As the cats eat the rats the cat population swells, and people pet their cats but hopefully not random rats....
This yahoo answers statement is funny, a guy quotes the defunct http://www.cats.com
page, which I'm not saying is unbiased or anything, but they look at it from a cats perspective.http://answers.yahoo.com/question/index ... 207AA20vbk
You see that little  up there at the end of the wikipedia portions? Where they reference their source material? Have you read it? It's a great article. And it says the EXACT OPPOSITE THING THE WIKIPEDIA ARTICLE SAYS.http://www.libraryindex.com/pages/2149/ ... ERIOD.html
The Persecution of Cats
Cats came under suspicion for a variety of reasons. Unlike dogs, they did not behave subserviently toward humans. This was considered unnatural, because it violated the biblical view that humans should have dominion over animals. Also, cats were very active at night and engaged in loud, raucous mating rituals. Though cats had always behaved in this manner, to the superstitious minds of the Middle Ages, cats were practicing supernatural powers and witchcraft. Most accused witches were older peasant women who lived alone, often keeping cats as pets for companionship. This guilt by association meant that roughly a million cats were burned at the stake, along with their owners, on suspicion of being witches.
In the early thirteenth century Pope Gregory IX (1145–1241) declared that a sect in southern France had been caught worshipping the devil. He claimed the devil had appeared in the form of a black cat. Cats became the official symbol of heresy (or religious beliefs not advocated by the church). Anyone who showed any compassion or feeling for a cat came under the church's suspicion. By the beginning of the fourteenth century, Europe's cat population had been severely depleted. Only semi-wild cats survived in many areas.
In 1347 the bubonic plague swept across Europe. Called the Black Death, it killed twenty-five million people (nearly a third of Europe's population) in only three years. Thousands of farm animals died as well, either from the plague or from lack of care. The death rate peaked in the warm summer months and dropped dramatically in the wintertime because the plague was being spread to humans by fleas on infected rodents. The plague revisited Europe several more times over the next few centuries. In addition, millions of people are thought to have suffered from food poisoning during the Middle Ages because of the presence of rat droppings in the grain supply. Centuries of cat slaughter had allowed the rodent population to surge out of control.
EDIT 2: Wikipedia user TimONeill edited the page on the 13th, replacing this correct information:
Perhaps his most lasting action was a minor item: his papal letter Vox in Rama of 1232 is credited with the vilification of cats, through its description of cult practices involving felines. This led to a great reduction in the number of cats, which, a hundred years later, may have contributed to the quick spread of the Black Death plague, which killed one-third to one-half of the population of Europe.
With those incorrect lies. Obviously somebody doesn't like bad things being said about Pope Gregory.