When American and Canadian diplomats fell ill in Cuba, the Trump administration suggested that they had been attacked by some form of secret weapon.
Conspiracy theorists obsessed over the idea that they may have fallen victim to a type of sonic ray, although officials in Ottawa refrained from such suggestions.
Now a Canadian study has suggested another culprit - a neurotoxin that originated from fumigation against mosquitoes during the Zika epidemic.
The incidents took place from late 2016 into 2018, and the United States in 2017 reduced its embassy staff to a minimum; Canada followed more recently.
The US cited the incidents and the danger posed to staff from what has become known as the ‘Havana Syndrome’.
The study, by a team of researchers affiliated with the Brain Repair Centre at Dalhousie University and the Nova Scotia Health Authority, studied Canadian victims and even the brain of a pet dog after its demise in Canada.
The research was the first to include diplomats for whom there was baseline medical testing from before their postings in Havana, so as to better compare with the tests from afterwards. Canada started implementing the practice after diplomats first started complaining of sickness.
The researchers said they had detected different levels of brain damage in an area that causes symptoms reported by the diplomats and which is susceptible to neurotoxins. They then concluded that cholinesterase, a key enzyme required for the proper functioning of the nervous system, was being blocked there.
Some pesticides work by inhibiting cholinesterase, the report said, and during the 2016-2018 period when diplomats became ill normal fumigation in Cuba was stepped up due to the Zika epidemic in the Caribbean.
The report said the diplomats’ illnesses coincided with increased fumigation in and around residences where they lived. One of the authors of the study, Professor Alon Friedman, clarified in an email to Reuters that both Canadian and Cuban authorities were fumigating.
“We report the clinical, imaging and biochemical evidence consistent with the hypothesis of over-exposure to cholinesterase inhibitors as the cause of brain injury,” the study concluded, while cautioning that other causes could not be ruled out and more study was needed.