A fifth monkey at the Tulane National Primate Research Center in Covington has tested positive for a bacterium considered by the U.S. government to have the potential to pose a “severe threat to public, animal or plant heath,” officials confirmed Wednesday.

The monkey, a rhesus macaque, was euthanized, and cultures from a necropsy were tested for Burkholderia pseudomallei. Preliminary tests indicated the presence of the bacterium, which causes melioidosis, a potentially fatal disease. The preliminary tests were confirmed Wednesday, officials said.

The fifth monkey’s infection and euthanasia were first reported late Tuesday by USA Today.

The macaque — known as IL88 — is the third animal to be euthanized in connection with the unexplained escape of the bacterium from the center’s laboratory, where experiments with it were conducted mainly on rodents. In November, two monkeys from the center’s 4,000-strong rhesus macaque breeding colony were infected.

One was euthanized. The other appeared to recover before suffering a relapse and being euthanized, as well. Tests on two other macaques, which have no signs of illness, showed antibodies consistent with exposure to the bacterium.

All five infected monkeys were treated in the same room at the center’s veterinary clinic, which is where investigators have focused their attention. How the first two monkeys were exposed to the bacterium remains a mystery — though one theory is that they were infected while being treated in the clinic for other issues.

IL88 was euthanized Feb. 23, according to an email sent from Scott Deitchman, of the federal Centers for Disease Control and Prevention, to state and local officials. Deitchman said he didn’t learn of the animal’s death until Feb. 28, and he informed state and parish officials the next day.

Tulane University spokesman Michael Strecker said Tulane notified state and local officials Feb. 28 when the preliminary tests came back showing IL88 was positive for Burkholderia pseudomallei.

While the investigation into how the bacterium got out of the lab continues, state and parish officials are making plans to closely monitor the area for any signs of contamination, said Mike Steele, a spokesman for the Governor’s Office of Homeland Security and Emergency Preparedness.

The Primate Center sits on 500 acres of prime real estate near the Abita and Tchefuncte rivers. Northlake Christian School is across the street, and three residential neighborhoods are nearby.

One of the monitoring plans includes testing rodents, raccoons and possums in and around the facility for the bacterium. Questions about the proposed testing posed to a Louisiana Department of Wildlife and Fisheries spokesman were referred to Steele, who said the exact procedures remain to be worked out.

Another proposal is to notify local veterinarians to be on the lookout for infections, using an information sheet listing the potential symptoms in animals, according to a U.S. Department of Agriculture spokeswoman.

In early February, a USDA investigator who had been at the Tulane center in late January reported symptoms that could have been caused by exposure to the bacterium. The symptoms were treated and she recovered, but subsequent blood tests to confirm whether she was exposed while at the Covington center or during previous travel to other areas of the world have been delayed, officials said. The bacterium is native to southeast Asia and northern Australia, where it is found in contaminated soil and water.

Individuals become infected with the disease through direct contact, usually with soil and water. Infection can be manifested in a number of symptoms, including fever, cough, chest pain, headaches and respiratory distress, among others. It is often mistaken for other diseases, which can complicate a correct diagnosis.

Follow Faimon A. Roberts III on Twitter, @faimon.