A boy raises the Cuban flag during a daily ceremony in Santo Domingo, Cuba. (Alexandre Meneghini/Reuters)

For two years, diplomats posted to Cuba have been suffering a mysterious illness.

They say they have heard painful, high-pitched noises and lost their hearing. “Some were asleep and awakened by the sound, even as others sleeping in the same bed or room heard nothing,” the Associated Press reported. Scores have reported headaches, dizziness, nausea and difficulty concentrating.

Douglas Smith, director of the Center for Brain Injury and Repair at the University of Pennsylvania's Perelman School of Medicine, evaluated 24 affected Americans. He said his patients looked “exactly like the patients we would see in a concussion clinic,” according to the CBC.​

His team has found “perceptible changes in [the] brains” of the victims, including changes to the “white matter tracts that let different parts of the brain communicate.” But none reported blows to the head.

Many of the victims reported trouble processing information. Some said they could not remember things anymore and struggled to come up with the right words when writing or speaking.

The symptoms have struck 24 Americans and 10 Canadians, including some minors. So far, investigators have not found their cause.

Initially, investigators suspected some kind of sonic attack. But they found little evidence of that. And scientists say acoustic waves have never been shown to alter the way the brain works. There has been suspicion that the ailment is something like a mass hysteria. But doctors say the changes to the brain that they see rule that out. They suspect it is a medical condition, though environmental assessments have yielded few clues.

Former secretary of state Rex Tillerson has suggested that the symptoms were the result of “targeted attacks.” But he could not say who was behind them. Neither could an investigation by the FBI. Cuban officials have denied any involvement in the ailments and have cooperated with investigators.

“Some U.S. officials have speculated that the 'attacks' could have been conducted by 'rogue' elements within the Cuban government or military, or by agents of an unidentified third country,” my colleagues report.

The United States has significantly reduced its staffing in Cuba. Last October, the U.S. State Department trimmed its embassy staff by half.

And this week, Canada decided that its diplomats should no longer bring their families to live with them in the country during their postings. The government said it took this step because of “new information” about the strange symptoms. All current staffers were notified Monday of the decision. Their families will be transported home in the next few weeks.

The Canadian Foreign Ministry said there is no evidence that tourists are at risk. The State Department, meanwhile, has warned Americans against visiting. It suggests, in particular, that travelers avoid two hotels where U.S. diplomats may have been hurt.