Rat poison theory in Thai tourist deaths

A 23-year-old New Zealand student, two elderly Britons and a 48-year-old Thai tour guide had all been staying at the Downtown Inn Hotel in Chiang Mai, 800 kilometres north from Bangkok, before their mysterious deaths in recent months.

Reports from New Zealand have suggested they were poisoned by a chemical used to kill bedbugs, but a senior Thai physician has told AAP that forensic investigations were widening to include insecticides capable of killing rodents.

Dr Surasing Visaruthrat, a deputy director at the Chiang Mai Public Health Office, said investigations had widened beyond the initial theory that a bedbug killer spray containing chlorpyrifos was responsible for the deaths.

Dr Surasing said investigations covered three hypotheses focused on a potential virus, chemical contamination or environmental factors that led to the deaths and illness.

"We have to look at another type of pesticide," he told AAP.

The New Zealand student, Sarah Carter, died on February 7 and her travelling companions Amanda Eliason, 24, and Emma Langlands, 23, fell gravely ill but later recovered.

Later in February, a British couple, George Everitt, 78, and his wife Eileen, 74, died from reported heart attacks at the same hotel.

The Associated Press reported that seven tourists had died in Chiang Mai earlier this year, and six of them had been staying in the same hotel in January and February.

The AP said the other victims were from France, the United States and Canada.

An independent investigation carried out in New Zealand and broadcast on New Zealand TV alleged traces of chlorpyrifos had been detected in the hotel rooms.

Chlorpyrifos is a restricted-use agricultural pesticide in the United States.