Officials at Denver Zoo in the US state of Colorado are taking precautions to avoid an outbreak of plague after a monkey at the zoo died of the disease.
Monkeys could be more susceptible to plague than other animals
The zoo's 17 remaining capuchin monkeys have been put into an isolated cage and are being treated with antibiotics.
Zoo officials suspect the monkey caught the disease from the carcass of an infected squirrel it may have eaten.
Several squirrels and a rabbit have been found dead of the disease in recent weeks near the zoo.
Veterinarians say there is little risk of the plague spreading to humans but visitors are being warned to avoid squirrels and rabbits.
None of the zoo's other monkeys or animals have shown symptoms of the plague.
The disease is normally found in some wild animals in Colorado during the spring, but usually in rural areas.
"We see it every year in wild rodents," said John Pape, an epidemiologist with the Colorado Department of Public Health and Environment.
"But it's uncommon circulating in tree squirrels in urban neighbourhoods, including metro Denver."
Plague is usually spread among rodents by flea bites, but humans can pick it up by eating an infected animal or handling its faeces.
Plague is endemic in many countries in Africa, in the former Soviet Union, the Americas and Asia, according to the WHO.
If left untreated, it has a case-fatality ratio of 30%-60%.
A form of plague - the Black Death - is believed to have killed millions of people in Europe in the early 1300s.