Researchers have traced a mystery illness that has been killing more than 100 Indian children annually to a tropical fruit.

For decades, seemingly healthy children in the Bihar region of northern India had been suffering sudden seizures and loss of consciousness, always during the scorchingly hot summer months of May and June, before the arrival of the annual monsoon rains in July.

Almost half of the affected children died, baffling doctors.

Research published on Tuesday has finally claims to have solved the mystery, suggesting the children were not ill, but had been poisoned by eating too many lychees on an empty stomach.

A joint investigation by India’s National Centre for Disease Control and the India office of the Centre for Disease Control and Prevention in Atlanta explains how beginning in 1995, the deaths were variously blamed on heat stroke, infections carried by rats, bats or sand flies, and pesticides used in the regions many lychee orchards.

Doctors were confused by the way the illness — although clustered in one small part of India — typically struck just one child at a time, leaving friends and even siblings unaffected.

According to the paper, published in the British medical journal The Lancet, the connection was finally made when epidemiologists studying children in hospital in the Muzaffarpur area heard about Jamaican vomiting sickness, an apparent illness that had caused brain swelling and convulsions in children in the Caribbean for decades until parents realised it was caused by eating too much unripe ackee fruit.

Researchers tested the region's lychees and discovered that they contained the same toxin as ackee, hypoglycin A.

The hungry children — many of whom were malnourished — are thought to have gorged themselves on fruit that fell from the trees in the commercial orchards during the lychee season, consuming the toxin, which inhibits the body's ability to produce glucose.

Young children, who are particularly susceptible, returned home full of fruit and turned down dinner, causing their blood sugar levels to plummet even lower.

Many woke screaming in the night, before experiencing convulsions and losing consciousness as they suffered acute swelling of the brain.

India elephants with knitted jumpers Show all 9 1 /9 India elephants with knitted jumpers India elephants with knitted jumpers Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra, India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Phoolkali and Laxmi (left) watch while the final touches are completed. Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Phoolkali and Laxmi (left) watch while the final touches are completed. Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Phoolkali and Laxmi (rear) show off their jumpers. Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Phoolkali Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Phoolkali and Laxmi (rear) show off their jumpers. Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Suzy, (front) Phoolkali and Laxmi (rear) show off their jumpers. Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Suzy, (front) Phoolkali and Laxmi (rear) show off their jumpers. Roger Allen India elephants with knitted jumpers Elephant jumpers. Badly treated rescued elephants at the Wildlife SOS sanctuary outside Agra India with their newly knitted jumpers are on show for the first time, they are all effected by the cold after their ordeal at the hands of owners. Suzy, (front) Phoolkali and Laxmi (rear) show off their jumpers. Roger Allen

In 2015, as a result of the investigation, health officials began urging parents in the area to be sure to feed young children an evening meal and to limit their consumption of lychees.