Almost 200 people in New Brunswick have been exposed to the mumps, according to the province's public health office.
Public health officials say someone who attended a wedding in the Saint John area was infected with the virus.
One case of mumps has been confirmed and officials are waiting for the test results from two other cases.
The case of mumps was confirmed on Friday and public health officer Dr. Scott Giffin said all of the wedding guests were promptly contacted.
Giffin says those who know the infected person could have also been exposed prior to or after the wedding.
"People should be calm and cool about this and they should see their family doctor if they develop any symptoms," said Giffin.
Those symptoms include painful swelling around the neck, a fever and a general feeling of being unwell.
"With mumps your infectious period is from the on-set of swelling in the neck for about five to seven days."
If left untreated, mumps could lead to sterility, particularly in men, neurological problems and hearing loss.