This is a sad story. There's been an outbreak of both parvo and a feline disease at a shelter in Las Vegas. The shelter has to euthanize 1,000 animals.
It turns out that the shelter wasn't vaccinated the animals properly, nor was it using the correct vaccines. To make things worse, the well-meaning shelter staff was trying to avoid euthanizing to give the animals a longer chance at adoption, so the conditions were overcrowded. The overcrowding helped spread the diseases.
http://www.cnn.com/2007/US/02/16/she....ap/index.html