It was in May that the mysterious illness first took hold.

In their isolated rainforest home in the Malaysian state of Kelantan, members of the Batek tribe, the country’s last indigenous nomadic community, began experiencing a fever and breathing difficulties. Then, one by one, they started dying.

Over the past month, 14 people from the tribe’s village in north-eastern Peninsular Malaysia have died, and more than 50 have been taken to hospital. Some are still in intensive care and more are being admitted by the day. Forty-seven others have been treated for respiratory problems.

The source of the illness in this small village of 300 indigenous people, known as the Orang Asli – a Malay phrase meaning “original people” – remains unknown. Local authorities have cordoned off the area as they investigate, testing for everything from infectious disease to pollution or poisoning from nearby mines, and have begun exhuming the buried bodies for postmortems.

Facebook Twitter Pinterest Children from the Batek tribe play in the jungle near their village. There are only 12 Batek settlements left in Malaysia Photograph: Zainal Abd Halim/Reuters

The cause of death in two of the bodies has been determined as pneumonia but investigations continue into whether it was a secondary infection. Locating the bodies of the Orang Asli who have died has proved difficult as their custom is to leave the community when they become ill, and many had migrated deep into the jungle.

“We are looking for the reason why there are so many deaths,” said the Malaysian prime minister, Mahathir Mohamad, on Monday. “There may be an infection of one type of disease but at this time we do not know what type of disease has caused their deaths.”

The Batek are one of Malaysia’s three remaining tribal groups within the indigenous Orang Asli people. Traditionally a nomadic tribe, there are only 12 Batek settlements left, with most living in close proximity to the Kelantan rainforest their ancestors called home. Due to poor access to healthcare, rampant deforestation of their rainforest home and being surrounded by pesticides from the palm oil and rubber plantations which have poisoned the land and their water supply, the Batek population has been in decline in recent years.

For those still living in the infected Kuala Koh settlement, an atmosphere of terror has gripped the village. “I am very worried,” a villager, Adidas Om, 32, told reporters on the steps of Kuala Krai hospital where he had brought his two young daughters, Hoi, six, and Boi, five, who were both experiencing breathing difficulties. “Apart from my children, my neighbours are suffering from the same disease and some have died.”

Facebook Twitter Pinterest A man from the Batek tribe goes hunting in the rainforest. The Batek population has been in decline, partly due to rampant deforestation of their home. Photograph: Zainal Abd Halim/Reuters

Another villager, Inja Punai, 32, told a local news site that villagers suspected their water supply had been tainted by nearby mining operations. “We have not made accusations but suspect that the water pollution is caused by chemical waste,” she said.

Adjacent to the Kuala Koh village there is an iron-ore mine, which an NGO, Sahabat Jariah, said had been polluting the area with chemicals used in explosions.

“Universiti Kebangsaan Malaysia had sampled the water in the rivers around the village and found the water is contaminated with metals, arsenic and chemicals from the fertilisers,” said Sahabat Jariah in a Facebook post about the plight of the Batek people in Kuala Koh. “The blasting ingredients are said to be processed near the water source of the village.”

Speaking at a press conference at Gua Musang hospital, the health minister, Dzulkefly Ahmad, did not rule out environmental poisoning. “There is a manganese mine in the area, and lung disease could be one of the illnesses caused by mining,” he said. Malaysia’s deputy prime minister, Dr Wan Azizah Wan Ismail, said the government would take “stern action” if it were discovered the tribe had been poisoned.

Dr Steven Chow, leader of the Federation of Private Medical Practitioners’ Associations Malaysia, said he had visited the Batek tribe in Kuala Koh in April and had found them in a state of neglect, suffering from gastrointestinal and fungal skin infections and without a supply of clean running water.

Chow emphasised that he did not think it was an airborne disease which had affected the tribe. “This was a community in total neglect,” he said. “Their water supply was virtually non-existent, sanitation was bad and they were suffering from all sorts of infections, showing their immune systems were very vulnerable. No effort had been made to help them.”

“I cannot confirm the reports that their water source had been polluted,” he added, “but I will say that this was a group of people who desperately need help.”