Three monkeys living at the Jacksonville Zoo and Gardens in Florida died last week from a Shigella infection, the zoo announced on Facebook.

The zoo announced on Thursday the “unexpected” death of 35-year-old Bulera, a female western lowland gorilla.

Bulera was said to have died from Shigella, a bacteria that causes shigellosis and symptoms such as diarrhea, vomiting, cramps and dehydration.

The infection is usually transmitted through contact with feces, food or water, the zoo said. While we “may never know the exact source” of Bulera’s infection, it could have been transmitted by an asymptomatic monkey or a staff member, which the zoo said was “unlikely.”

The zoo said that Shigella can be more severe in monkeys because it is harder for them to fight the infection.

When Bulera died, other monkeys were also showing symptoms due to the highly contagious nature of Shigella and were in “various stages of treatment and recovery,” the zoo said.

Despite efforts to care for the sick monkeys and the use of “personal protective equipment and regular hygiene to prevent further spread,” two more monkeys, the bonobo brothers Jumanji and Jenga, died on Monday, the zoo said.

Jumanji and Jenga, born in 1996 and 2011 respectively, suffered from heart problems that made them vulnerable to the infection, the zoo said.

The zoo recognizes how difficult it is to lose three primates in one week and said its staff is working to help the still-ill monkeys recover.

“Although many of the monkeys are at varying stages of treatment and recovery, we have made significant progress thanks to the hard work and resilience of our team,” it said.

It said animal health and care teams continue to “closely monitor” the situation as Shigella can be characterized by periods of improvement and then relapses.

This article was originally published on NBCNews.com.