Canada has summoned families of diplomats from the Cuban capital of Havana , after a number of embassy employees suffered from mysterious and unusual health problems. 

Government officials issued the summons because 10 Canadians still show symptoms such as dizziness, nausea and difficulty concentrating, the BBC reported. 

According to a Canadian medical specialist, these symptoms may be associated with a new type of brain injury. 

Twenty-one US diplomats in Cuba suffered similar symptoms last year. Washington recalled its staff in September and issued a travel warning to Cuba. According to officials, those who appeared to be recovering from the disease saw the symptoms reappear, the BBC says .




It was originally thought that these mysterious diseases were caused by secret audio attacks. So that ultrasound can cause hearing loss and physical pain by making an inaudible sound to the human ear in the vicinity of the victim. Research is under way to ascertain the cause of these diseases.