Twelve dogs at a Denver animal shelter contracted pneumonia of unknown etiology and five of them have died, prompting the facility to close for at least 30 days while veterinarians investigate the extent of the illness and try to find the causative agent. "It's obviously very stressful for us, the staff. But ... this is what we're here to do. We're here to help animals in our community," said veterinarian Cathlin Craber. One-quarter of the 260 dogs in the shelter are estimated to be ill.