A mysterious illness that has plagued embassy in Havana, Cuba, starting in 2016, remains unsolved. And though "sonic weapons" and viral attacks have been declared unlikely culprits by researchers, no cause seems to explain the dizziness, headaches and other cognitive issues experienced by some U.S. and Canadian embassy workers and family members there.

Now, the Canadian government has declared their embassy an "unaccompanied post," officials announced Monday (April 16). "This means that Canadian diplomats posted to Cuba will not be accompanied by their dependents," Global Affairs Canada said in a statement, adding that they will review all Canadian diplomatic positions in Cuba, "with a view to balancing our duty of care to our staff members and their families, with the ongoing need to deliver services to Canadians in Cuba, and to promote and protect Canadian interests there."

In the fall of 2016, embassy workers stationed in Havana have said they heard loud, strange noises that were described in a Washington Post article as chirps, hums and scraping sounds, or that they felt a ghostly breeze around them. Soon after, those affected reported having hearing loss and ringing in the ears. Other symptoms have included cognitive impairment, headaches, and balance and sleep issues, Live Science previously reported.

The Associated Press reported in 2017 that doctors had found changes in the brains of those experiencing the symptoms, particularly in the white matter region of the brain. The white matter is made up of spindly appendages on some brain cells that transmit electrical signals and allow these cells to communicate with one another.

Doctors at the University of Pennsylvania examined 21 U.S. embassy workers in Havana, documenting the various cognitive symptoms. In that study, published Feb. 15 in the journal JAMA, the researchers concluded that the proposed culprits, including sonic weapons, could not explain the symptoms.

In September 2017, the U.S. State Department ordered all nonessential personnel and families leave Cuba — about a 60 percent reduction in staff, CNN reported at the time. The department also urged Americans to avoid travel to Cuba due to the mysterious illnesses, according to the CNN report.

However, the Canadian government indicated travel to Cuba appeared safe for now: "There is no evidence to suggest that Canadian travelers to Cuba are at risk." For the latest updates for Canadian travelers, check out the Government of Canada Travel Advice and Advisories.

Originally published on Live Science.