J.A. Happ beat the Royals in his Yankees debut Sunday. (Noah K. Murray/USA Today)

Pitcher J.A. Happ, acquired by the New York Yankees in a trade late last week, has been diagnosed with hand, foot and mouth disease, becoming the second Major League Baseball pitcher afflicted over the last two weeks.

Happ was diagnosed with what the team said is a mild case; it is unclear how he came down with a viral disease most common among children under the age of 5. One possibility is that he was infected on a commercial cross-country flight after being traded Thursday by the Toronto Blue Jays.

“I got a call from our trainer,” General Manager Brian Cashman told reporters. “He said, ‘I’m not sure what’s going on here, but J.A. Happ has some complaints. He’s not feeling right, and he had noticed some blistering.’ ”

Mets pitcher Noah Syndergaard was the first player afflicted this summer. He was placed on the 10-day disabled list with the illness, which is highly contagious, on July 22 after a start at Yankee Stadium. The Mets believe Syndergaard came down with the disease when he visited a kids’ camp over the all-star break. Syndergaard is expected to be activated Wednesday.

The Yankees do not, for now, plan to place Happ on the disabled list. Happ is 11-6 after winning his Yankees debut Sunday, and Cashman said he “probably” would be able to start against the Red Sox in the four-game series that begins Thursday at Fenway Park. He is scheduled to pitch Saturday.

“I can only convey to you what our internist who evaluated Happ conveyed to me,” Cashman said. “He feels currently this is a mild case, but he’ll stay connected. We’ll be in a better position [Wednesday] to evaluate whether this is toward the tail end of this thing or if it’s ramping up.”

For Syndergaard, one clue that he was ill came during a start in which the velocity of his pitches was low and he was having trouble breathing. Happ complained of blisters on his hands when he arrived at Yankee Stadium and was sent to New York Presbyterian Hospital. Symptoms, according to the Mayo Clinic, can include fever; sore throat; malaise; painful, blister-like lesions; and a red rash. Although people afflicted with the virus are most contagious during the first week, it can remain in the body for weeks after symptoms and signs are gone. Some people — especially adults — can pass the virus (often by coughing or sneezing) without showing any symptoms of the ailment.

“There’s no real treatment. You just monitor the patient and let the virus take its course,” Cashman said. “He’s still scheduled to start. That’s not something that as of now is in jeopardy as of yet. . . . [O]ur internist felt if everything is as is right now, he probably would be able to go on Saturday. But it’s a to-be-determined story.”

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