Two more NHL players -- New Jersey Devils center Travis Zajac and defenseman Adam Larsson -- have been diagnosed with the mumps as the league continues to face the unusual outbreak of the vaccine-preventable disease.

Though Zajac's diagnosis, first reported by The Bergen Record, was only recently confirmed, he is already over the disease and is back to skating on his own, a team representative confirmed to ESPN.com.

Larsson, however, is still recovering and is quarantined from the team, per league-recommended protocol.

The Devils' Travis Zajac, center, who has four goals and four assists this season, has had the mumps but is back to skating on his own. Bruce Bennett/Getty Images

Zajac and Larsson are the latest in the group of NHL players to be diagnosed with the mumps. Five members of the Minnesota Wild battled the disease, while both Corey Perry and Francois Beauchemin of the Anaheim Ducks were also diagnosed. The New York Rangers had one confirmed case -- Tanner Glass -- and the St. Louis Blues had at least a few cases that went unconfirmed.

The league sent out memos in mid-November to all NHL clubs, in coordination with the NHL's infection control subcommittee, to remind teams' medical staffs and head trainers of the recommended protocol and guidelines for diagnosis and prevention.

It is not immediately known where or when this particular outbreak began within the NHL, and it is unclear just how long the problem could persist.

One of the main difficulties with the mumps is the lengthy incubation period, where an affected person may have symptoms and be exposing others to risk without knowing it.

Mumps is treated domestically with the mumps-measles-rubella vaccine, but it has about an 88 percent effectiveness rate, according to epidemiology expert Dr. Greg Wallace, who leads the team at the Center for Disease Control and Prevention in Atlanta.