Use of pesticide linked to mystery illness affecting Canadian diplomats in Cuba

Researchers in Canada believe that excessive use of pesticides may be to blame for a cocktail of unexplained neurological symptoms that struck down Canadian and US diplomats in Cuba.

More frequent spraying of pesticides during the Zika virus outbreak that swept thought Latin America during 2016 and 2017 may be the cause of the mystery illness, dubbed Havana syndrome, the paper says.

In 2017 US and Canadian diplomats began to complain of a range of neurological symptoms including tinnitus, dizziness and headaches. Sufferers also reported trouble sleeping and even hallucinations.

A dog belonging to a Canadian diplomat's family was even affected and had to be put down.

US staff reported hearing an overwhelmingly loud, painful noise before the onset of the mystery illness, while the Canadian diplomats mainly reported more gradual symptoms. A study of US sufferers published earlier this year found that sufferers brains had shrunk.

US staff in China raised similar complaints last year, prompting concerns that they had come under a deliberate "sonic attack". The mystery illness prompted the US to halve the numbers of staff at its embassy in 2017.

Researchers at Dalhousie University in Canada were tasked by the Canadian government with investigating Havana syndrome and in a paper released this week they say that those affected may have suffered brain damage linked to exposure to pesticides.

At the time the diplomats fell ill the Zika virus, which is transmitted by mosquitoes, was sweeping through Latin America and embassy records show that diplomatic residences and buildings were fumigated frequently  in some cases up to 25 times a year.

The researchers studied 26 Canadian diplomats and their family members who all had neurological symptoms.

Scans show that those suffering the syndrome had damage in a region of the brain and subsequent tests revealed traces of an insecticide used in Cuba against mosquito larvae.

Researchers identified cholinesterase inhibitor toxicity as the likely cause of the damage. Cholinesterase is an enzyme responsible for the vital functioning of the nervous system and certain classes of pesticide, such as organophosphates, are designed to attack it.

Alon Friedman, professor of neuroscience at Dalhousie and lead author of the paper, said that the research team began the study with a completely open mind.

"But we came to the conclusion exposure to pesticides is the most likely explanation. Some of the patients thought this made sense, some didn't," he said.

"We found out how the the fumigation was done - up to 25 times a year in some houses - and the products that were used and we realised this would never happen in North America or Europe," he said.

Prof Friedman added that further study would include looking at local populations in Cuba to see if they suffered similar symptoms.

He said that it was well known that certain pesticides were linked to neurological problems, with similar symptoms seen in soldiers with Gulf War Syndrome - a cocktail of conditions suffered by those serving in the first Gulf War.

The cause of the syndrome has never been properly explained but some think it is linked to the use of chemical weapons.

The paper concludes: "The clinical course, pattern of injury, brain regions involved, cortical and sub-cortical dysfunction, together with a history of common exposure, all raise the  hypothesis of recurrent, low-dose exposure to neurotoxins.

“While proving the source of exposure and cause of injury is difficult, if not impossible at this time point, Canadian embassy records furthermore confirmed a significant increase in the frequency of fumigations around and within staff houses beginning January 2017, concurrent with reported symptoms,” the paper said.

Jon Stone, professor of neurology at the University of Edinburgh, said the Canadian researchers’ findings were interesting but did not point to a specific “Havana syndrome”.

“Since they don’t have any data on staff who were also exposed to the fumigation but didn’t have symptoms then it remains a hypothesis,” he said.

He added that symptoms such as headache, poor concentration and dizziness were common in the general population for a variety of reasons such as migraine.

“We aren’t told what proportion of the Canadian citizens were symptomatic so we don’t know whether there are truly more people who are feeling unwell than you would expect from chance,” he said.

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