Last month, a Dutch rabbit at the Tilden Park Little Farm started acting strangely. It had lost its appetite, lying in its hutch, head hanging, refusing to move. When staff at the free education farm in Berkeley examined the animal, they saw one of its eyes had swollen immensely.
Jenna Cassel, a naturalist at the park, was disturbed. Animals get sick, sure, but this was unusual. She took the rabbit to a veterinarian and was shocked by the diagnosis.
The rabbit had contracted myxomatosis (mix-a-mitt-oh-sis), a viral illness endemic to a narrow strip of the U.S. ranging from Oregon down the California Coast to Baja. Although relatively harmless to wild brush rabbits, the illness is highly contagious and has a 99% mortality rate for domesticated species. Suddenly, it was threatening the beloved rabbits of the farm.
“I asked a ton of questions because I had no idea what was happening,” Cassel said. “They said it’s very contagious. Very deadly.”
Cassel learned that rabbits suffering from the illness experience swollen eyes and genitalia, ulcers, fever and, eventually, death. Even before leaving the vet, she was on the phone with staff at the farm, trying to quarantine the surviving rabbits.
But it was too late — at least two or three others already had contracted the illness. The remaining handful, who had been exposed but weren’t showing symptoms, were euthanized to save them from the ravages of the virus. And so, by the end of November, Tilden Park’s farm was left with no rabbits for the first time in decades.
“It was really hard,” Cassel said. “When we lose any of the animals, it’s really heartbreaking. They have names. We get really attached to them.”
Tilden Park’s Little Farm has been around since the 1950s, established to teach city children and their families about farm animals. The farm is unique in its location, situated within a 740-acre nature preserve amid a broader 2,000-acre park.
Until now, that location has served as a boon — a farm at the base of a hidden canyon disconnected from the bustle of the city. But it is just this kind of location that likely led to the spread of myxomatosis.
“The infections only occur where the brush rabbit’s territory is,” said Hilary Stern, a veterinarian at the Exotic Pet Clinic in the Santa Cruz Mountains, who has been studying the illness. “So it usually tends to be on the outskirts or in the mountains.”
Because the virus is carried by the wild cottontail rabbit, infections occur where domestic species and wild rabbits coexist. The rabbits at Tilden Park’s Little Farm are kept in an enclosure outside, so it’s possible they were infected by fleas or mosquitos.
The virus is still something of a mystery. Although it has been in the Bay Area for as long as we know, many veterinarians still don’t even know of its existence or understand its spread.
“It will be on the westside of Santa Cruz, then the next year it’s up in the mountains, and then it will be in Los Gatos,” Stern said. “It is odd.”
Over the decades, flare-ups of myxomatosis on the West Coast have periodically gained attention. In the 1970s, there were numerous cases in Davis. In 2010, three cases were reported in Los Angeles, prompting their health department to issue a warning. In 2016, the illness killed all but one of a herd of 90 rabbits in Roberts Creek, Oregon. Other farms in the Bay Area also have been affected, including Deer Hollow Farm near San Jose, another farm situated within a park system. The virus is not a threat to humans or other animals.
But the current spread is enigmatic.
“It’s hard to say where it is and where it isn’t,” Stern said. “A lot of people don’t know about it, so they may be missing the diagnosis.”
In Berkeley at least, the dearth of infections over the decade at the Little Farm seems to indicate myxomatosis was previously rare in the area. Now experts say families with rabbits should take extra precautions. Although there is a vaccine for the virus in Europe, none exists in the U.S.
That reality has staff members at the Little Farm wondering whether they can safely host rabbits again. Cassel said the farm will wait at least four months before introducing new ones. The farm also plans to research new housing methods to keep the rabbits safe. The very earliest the animals would return is April, but nothing is assured.
Tilden Park’s Little Farm is a popular attraction for families during the holiday season, and rabbits are one of the primary draws. For some children, interacting with a rabbit at the Little Farm will be the first time touching such an animal. The furry little creatures have been a tactile, charismatic part of the program, a farm that has introduced generations of East Bay residents to life beyond the city.
“It’s a big loss. I know our visitors feel that loss,” Cassel said. “We definitely want to try to have rabbits in the future. But it’s going to take a long time to think about it.”