When Matthew Lloyd volunteered to take part in clinical trials to help find a vaccine for malaria, he was signing up for a project which it is hoped could one day eradicate a disease that kills one million people each year.
Now it is feared that the 35-year-old nurse's sudden unexplained disappearance half way through the pioneering medical project could put his own life at risk.
Yesterday the family of the unmarried man, who was injected with the potentially fatal disease as part of the long-running public-health experiment, made a televised appeal pleading with him to seek urgent medical attention after apparently walking out on his job at Southampton General Hospital where he had phoned in sick.
It is understood that Mr Lloyd, described by his parents as "responsible, ambitious and focused", was taking part along with seven others in a trial in Oxford, but had failed to turn up for an appointment there last week. He had been due to receive potentially life-saving anti-malarial medicine to protect him from the effects of the disease.
His parents, Michael and Doreen Holland, described his going missing as totally out of character. "We regularly speak to him on the phone, by text and by email and we knew he was taking part in these clinical trials; he told us about it back in July.
"We were totally shocked to find out that he had not turned up to his appointment in Oxford on 7 October. It is not like him to take on a project and not follow it through. He was quite excited about taking part in these trials. He was doing this as a way of getting more experience and a means of furthering his career as a nurse," they said.
Malaria is the leading killer of children under the age of five in sub-Saharan Africa and is caused by a parasite transmitted by the female anopheles mosquito. About 500 million cases of the disease occur every year, mostly in the developing world and the discovery of a vaccine has become one of the great goals of modern medicine.
Oxford University said patient confidentiality rules meant it could not confirm whether Mr Lloyd was taking part in its world-leading vaccine studies.
They have been taking place for the last decade under the direction of Professor Adrian Hill at the Jenner Institute, supported by charities including the Bill and Melinda Gates Foundation, which was set up by the Microsoft billionaire and his wife.
Under its current research programme, which is being carried out jointly with Imperial College London and Southampton University, participants are divided into two groups. In blind trials one group is given the candidate vaccine and the remainder a placebo to act as a control. They are then injected with a strain of malaria which is non-contagious and fully treatable using standard over-the-counter anti-malarial drugs. They are then monitored to see to what degree the vaccine offers protection. Participation in the blind trials can last for between three and 12 months.
Police, who broke down the door of Mr Lloyd's one-bedroom flat in Southampton to search inside when the alarm was first raised, believe he may have travelled to London and have also tracked his movements to Birmingham and Milton Keynes where his bank card was used. He is also known to have friends in Cornwall and Somerset.
Det Insp Dave Jackson, of Hampshire police, said: "Our concerns for Matthew's health are increasing because he needs urgent medication, which he does not have with him.
"Even the smallest detail could prove crucial in finding Matthew so he can receive his life-saving medication in time."