When I visited the Occupy SF camp a couple of weeks ago I saw many people who seemed to be chronically homeless, displaced and forgotten on the streets. It’s easy to understand how, for many people surviving without homes, the companionship of a dog or cat may be crucial to their well-being. all the more reason to help make that companionship possible and healthy for the animal as well.

So on Monday we hosted our third free veterinary clinic at Occupy SF, where tight living space provides a potential breeding ground for diseases. besides identifying the parvo cases, we noted several dogs with signs of respiratory disease (kennel cough) and others with giardiasis symptoms. Kennel cough, which is highly contagious to canines, manifests itself with a dry “honking” cough, nasal discharge, and general malaise that may progress to pneumonia. Giardiasis, caused by a protozoan parasite, may be transmitted to humans, depending on the Giardia subspecies. its chief symptom in both humans and dogs is diarrhea, and can lead to severe complications. like parvo, it spreads via infected feces.

Four of our newest canine patients at the SF SPCA Veterinary Hospital came to us from Occupy San Francisco encampments. Two were brought to the Leanne B. Roberts Animal Care Center on Monday and another arrived today; like the first dog, they’re suffering from parvovirus infections. all are receiving treatment and their prognosis is guarded.

Animal people know all about “parvo,” and dread it. It’s a highly contagious and often fatal disease that mostly affects young dogs and puppies under the age of six months. (Cats get a different form of it.) The symptoms include vomiting and bloody diarrhea. there is a highly effective series of parvo vaccines, but puppies have to get the whole series to be immune. Vets warn that until the pups reach 16 weeks of age and have received all their shots, they shouldn’t be allowed to walk on grassy areas or be near other dogs that aren’t vaccinated. Parvo can survive on the ground for many months, making it easy for unvaccinated puppies to catch the disease from contact with an infected dog or area.

Parvo is difficult to treat—it often entails five to seven days of intensive care and the cost discourages many guardians from treating their pets at all. like many resourceful microorganisms, canine parvovirus (CPV) has undergone a couple of mutations that have given it an even greater ability to replicate and spread. The disease emerged in the late ’70s with a full suite of adaptations: for instance, dogs may carry the virus on their coats for long periods, and the virus can remain viable in the environment for months. Initially the virus replicates in lymph tissue (lymph nodes) and then is disseminated into the intestinal crypts. there, it destroys intestinal cells, robbing them of the ability to absorb water and nutrients. also destroyed are immune cells, leaving the pup susceptible to secondary bacterial infections. Despite aggressive treatment, which focuses on rehydration and restoring electrolyte balance and preventing those secondary infections, many dogs die of parvo.

We’re trying our best to address disease in the encampment. Simply put, it’s dangerous to bring an unvaccinated or undervaccinated puppy or kitten into any crowded, stressful environment. We’re deeply concerned about the spread of these diseases at Occupy SF, and strongly advise protesters not to bring their animals to the camp.

We encourage protesters to figure out a way among themselves to look out for the welfare not just of needy people but needy animals. it could be a matter of life or death for those cats and dogs. Some protesters need to choose whether it’s worth the risk to their companion’s life to keep a pet at the encampment under such difficult conditions. as an animal welfare organization, we’ll continue to do what we can to keep dogs and cats healthy, to encourage responsible pet guardianship, and to champion the value of the human-animal bond.