KAMPONG SPEU, Cambodia - When the phone rings, former Khmer Rouge soldier Ken Mon grabs a bag stuffed full of medicine, jumps on his motorbike and heads for an impoverished Cambodian village with the haste of any diligent local doctor.
Yet the 55-year-old Mon has no formal medical training.
While 'doctor' is a self-granted title for Mon, he - and others like him - are the only source to treatment for thousands of poor residents in Ang Ro Ngeang village, about 70 kilometres (45 miles) south of Phnom Penh.
Undeterred by his lack of qualifications, Mon drives ten minutes down a bumpy track in Cambodia's southern Kampong Speu province, arriving at the home of Chei Tana, 27, who complains of crippling stomach pains.
"You have a lot of air inside your stomach," he explains after examining his patient, giving him a packet of antacid pills.
Mon is one of hundreds of unlicensed doctors treating patients across a country whose medical system was eviscerated under the brutal Khmer Rouge regime of the 1970s and is yet to build a comprehensive public system.
Seventy per cent of Cambodians seek healthcare from the private sector - including from pharmacies, illegal doctors or traditional healers, known as "Kru Khmer" - according to a 2012 survey by the World Health Organisation.
But illegal doctors have fallen under intense scrutiny after a mass outbreak of HIV at a remote village in western Cambodia last November.
Authorities say the original infection was caused by an unqualified doctor, Yem Chroeum, who has admitted he re-used needles and syringes.
More than 200 of his patients have since tested positive for HIV and Chroeum faces trial on charges of murder, deliberately infecting people with the virus and operating an illegal clinic.
The scandal saw the government vow to crack down on unlicensed health providers.
Their practice "affects the lives of the people, and the reputation of the country", according to Sok Srun, director of the health ministry's hospital services department, which oversees the licensing of medical staff and clinics.
Slaughter of doctors
Despite their concerns, officials are yet to come up with a policy to persuade newly-trained doctors to leave the relative comforts of the cities and head into Cambodia's remote, rural hinterlands.
Neither have they been able to adequately boost the ranks of doctors, a profession decimated by the Khmer Rouge who slaughtered a huge proportion of the country's educated classes.
That legacy still haunts the country today.
World Bank figures say Cambodia, one of Asia's poorest nations, has just 0.2 doctors for every 100,000 people, on a par with Afghanistan.
Similarly impoverished Myanmar has 0.4 per 100,000, while France boasts 3.2 per 100,000.
For millions of Cambodians, doctors like Mon are their cheapest -- and often only -- option.
"I learned my medical skills at the university of life," he told AFP, adding authorities have never stopped him practising medicine.
Ironically that education came from the same people who destroyed Cambodia's health system.
Mon joined the Khmer Rouge as a fighter in 1974, shortly before the hardline communist regime seized power.
When it was finally toppled in 1979 -- after causing the deaths of up to two million Cambodians through execution, starvation or overwork -- he and many other cadres fled to Samlot, a stronghold on the Thai border.
There he learned his medical skills, first from Khmer Rouge medics and later from foreign doctors working for the Red Cross.
"The first day, they gave me a syringe and medicine and asked me to inject a wounded soldier," he recalls, adding he can now deal with a myriad of procedures from treating diseases such as malaria and typhoid to suturing wounds.
'We trust him'
Nuch Dy, a 56-year-old widow from a nearby village, has never seen a qualified doctor.
"(The health centre) is far and I don't have money to pay immediately," she says.
Instead she treats her long-time stomach problems with painkillers and antacid pills bought from Mon - often on a tab.
Neighbour Uon Sreang, 35, tells AFP that everybody in the village is aware their doctor has no formal training.
"But we trust him. He always used new syringes and needles when he gave injections to my family members," she says, her nine-month-old baby in her arms.
There is a logic to their faith in Mon's skills with official health centres often failing to guarantee a better quality of care.
The WHO has said that 43 per cent of the 11,000 health centres across Cambodia - the first port of call for medical treatment - are unable to provide full services due to a lack of physicians, medicine or equipment.
Meanwhile, a World Bank survey last year found only one in three official doctors in rural health centres were able to correctly diagnose a series of illnesses.
Of those who could, just 17 per cent were able to prescribe relevant drugs.
For the seriously ill - and the very young - a city clinic is almost always the only option.
Outside a children's hospital in Phnom Penh, Heng Hen, 45, waits patiently with three sick grandsons after making the 80 kilometre (50 mile) journey at dawn.
"Medics in the countryside don't have ability to treat children yet," Hen says.
He admits the recent HIV outbreak has given him pause for thought over the wisdom of continuing to seek treatment from unlicensed medics.
"But we have no choice because we are poor," he says.