The World Health Organisation is under growing pressure to reverse its opposition to the use of experimental ebola treatments. The apparently rapid response of two US aid workers to the drug ZMapp - the first time it has been used in humans - has led to calls from some doctors for it to be used more widely. The WHO will assemble a panel of medical ethics experts next week to consider the risks and benefits of using a drug that is so new it hasn't been assessed in clinical trials. It's uncertain whether the two patients owe their lives to the drug or whether they would have survived the virus anyway, as 40% of those infected in the current outbreak do. So doctors need to be sure they wouldn't cause additional harm by treating patients. ZMapp is a biotech treatment composed of three antibodies. One alerts the immune system to ebola-infected cells. The other two seem to prevent the virus from making more copies of itself, in effect neutralising it. Tests on monkeys suggest the drug works, but it needs to be given as soon as possible to the patient exposed to the virus. ZMapp is made using a process that sounds like science fiction. First, mice are infected with ebola and the immune cells that produce specific antibodies against the virus are removed. The antibodies are altered to work inside the human body by tweaking the DNA. Then the DNA is inserted into leaf cells of tobacco plants. The plants produce the antibodies as they grow. But it's several weeks before the plants are ready to be harvested and the drug distilled. The companies are looking at ways of speeding up the process. Even then there wouldn't be enough to treat every patient. And that raises another tricky question: Who is at the front of the queue? It's likely that it would be reserved at first for doctors and nurses. Some may feel that it's morally repugnant not to have equitable treatment. Others argue that health workers are putting themselves at extraordinary risk by treating victims of the virus - and they should be offered some security of treatment. It's a dilemma that the WHO's ethics experts will have to grapple with.