The Vancouver Canucks are offering mumps booster shots to players and disinfecting all their dressing rooms, after seven players and a trainer came down with symptoms of the highly contagious illness.

The Canucks announced Sunday that two more players and a trainer are experiencing mumps symptoms, days after five other players became ill.

So far, Troy Stecher is the only player with a confirmed case. But fellow defencemen Christopher Tanev, Nikita Tryamkin, and Ben Hutton as well as forwards Mike Chaput, Anton Rodin and Markus Granlund are also ill with suspected cases.

Dr. Reka Gustafson, the medical officer of health of Vancouver Coastal Health, says all of the players began showing symptoms around the same time.

“Our best bet is that these individuals got exposed to somebody who was infectious with mumps all at the same time,” she told reporters Sunday.

The affected players have been asked to quarantine themselves at home for five days to avoid infecting others while they await blood and oral swab test results to confirm infection.

Mumps is caused by a highly contagious virus that is spread through coughing, sneezing or coming into contact with saliva, such as by sharing water bottles or water fountains.

The vaccines against mumps, the MMR or MMVR vaccines (measles-mumps-rubella-varicella), are highly effective, but two shots are required for best protection. Still, even those who have been fully vaccinated can sometimes contract the illness.

There are currently several clusters of mumps cases in Canada, including in Ontario, Nova Scotia, and Alberta, where seven players and a coach with the Medicine Hat Tigers of the Western Hockey League have been infected.

The majority of those infected have had only one of the two needed shots, with many unaware that they were not fully immunized. That’s because, when the MMR vaccine was introduced, public health officials thought that only one dose was needed, but it later became clear that two offered better long-term effectiveness.

Public health officials are now urging all Canadians between the ages of 18 and 35 to ensure their vaccinations are up to date.

The Canucks, meanwhile, are offering booster shots to players, and disinfecting all dressing room areas to avoid further spread.

Mumps causes salivary glands to swell, leading to puffy cheeks and a swollen jaw. Other symptoms of infection include fever, headache, fatigue and muscle aches.

Symptoms typically appear 16-18 days after infection, but can begin as late as 25 days after exposure to the virus.

Complete recovery can take several weeks. In rare cases, the illness can lead to encephalitis, meningitis, or hearing loss. Pregnant women infected during the first three months of pregnancy are at risk of miscarriage.