Doctors have concluded that excessive use of agricultural insecticides was the "most likely" cause of brain inflammation that caused the death of 13 children.

Doctors investigating a fatal outbreak of Acute Encephalitis Syndrome (AES) in Bangladesh that killed 13 children, have blamed "excessive and improper applications of insecticides and other agriculture chemicals" in lychee fruit orchards. All 13 fatalities, which occurred within 20 hours of the onset of symptoms, were linked to exposure to lychee, a small, reddish fruit with a sweet white flesh that is cultivated across China and South Asia. Writing in the American Journal of Tropical Medicine and Hygiene, Dr M. Saiful Islam says the outbreak of AES, a condition associated with deadly inflammation of the brain, was initially attributed to a naturally occurring toxin found in lychee seeds and pulp:

"Our investigation suggested the seeds might not be the cause as the seeds are not eaten in Bangladesh and instead found the deaths were most likely due to an exposure to multiple, highly toxic agrochemicals. These deaths occurred at a time when lychee was being harvested and consumed across Bangladesh. If the seeds were the cause, then we would expect to see cases scattered across the country, not just in a certain small area."

Dr Islam and colleagues from the Institute of Epidemiology, Disease Control and Research and the United States Centres for Disease Control and Prevention carried out an exhaustive investigation into 14 cases of AES in children ranging in age from one to twelve years old. Only one child survived. According to the study, 13 of the 14 children lived either right beside or within ten metres of a lychee orchard. One of the victims did not live close to an orchard, but, before falling ill, he reportedly consumed a large number of lychees collected from the same orchards. The scientists discovered that around the time of the outbreak, growers were applying Endosulfan in the orchards, a "highly toxic" insecticide that has been banned due to its adverse health effects in more than 80 countries. As of last year, Bangladesh was one of several countries, including the United States, that still allowed restricted use of Endosulfan. The pesticide was slated to be phased out of use in the United States by the end of 2016. The outbreak occurred around harvest time, when there is typically an abundance of lychee fruit on the ground around the trees. Local residents told the investigators that it was common for children to play in the orchards and to eat fruit that had fallen on the ground without washing it, using their teeth to peel the lychee's tough skin. In addition, several of the victims had family members who worked in the orchards, which, Dr Islam notes, could have increased exposures via residues on clothing worn into the home. Several families of victims reported the symptoms began with a sharp, sudden cry from their child. Loss of consciousness occurred, on average, about 2.5 hours after the onset of illness and deaths within about 20 hours or less. Other symptoms included respiratory distress, froth at the mouth and convulsions. While it is known that an infection like meningitis can lead to AES, the scientists asserted that the "short duration between onset of illness and death all suggest the outbreak was more likely due to a toxic poisoning than an infection." Islam said physical evidence collected from the orchards, which included discarded containers of insecticides and other chemicals, and interviews with community residents suggested that multiple chemicals were applied to the fruit and in amounts far greater than are normally used by other lychee producers. The study also found evidence that the lychee growers were applying an insecticide that had been approved only for use in cotton, not food crops.

"People in the communities told us that sometimes the spraying was so heavy it became difficult to stay in their houses and that the smell would linger for hours."

Dr Patricia Walker, a specialist in refugee and immigrant health care, says the children's deaths were tragic:

"By working closely with the affected communities and earning their trust, researchers were able to identify the potential role of agricultural chemicals in this outbreak. Community education and improved oversight of pesticide use will be needed to help reduce the risk of future tragedies."