A test has been developed which could help detect the potentially fatal disease sleeping sickness.
Sleeping sickness is rife in Africa
The disease, seen mainly in sub-Saharan Africa, can be difficult to diagnose until it is fairly advanced.
But experts at London's St George's Medical School, writing in The Lancet, say the blood test they have developed could be carried out much earlier.
However, other scientists have questioned whether it is too "high-tech" to be used widely.
Sleeping sickness affects up to 500,000 each year.
It is a chronic, progressive disease which, unless treated, usually results in death.
The World Health Organisation estimates that 66,000 people die from the disease every year.
Establishing an effective test is important to avoid unnecessary administration of drugs, which can have serious and sometimes fatal side effects.
Sleeping sickness is spread by the tsetse fly and is caused by a parasite called trypanosome which is carried by the tiny creature.
Once in the blood stream it attacks the blood and nervous system.
Conventional tests for sleeping sickness involve blood tests to check for the presence of antibodies or parasites.
However, Professor Sanjeev Krishna and his team in London have discovered a way of diagnosing the disease by extracting serum from the blood and checking for a specific pattern of proteins that are detected using a sophisticated machine called a mass spectrometer.
This characteristic signature of protein patterns gives a "fingerprint" to the elusive killer.
The technique has been used to test for ovarian and other cancers, but this is the first time an infection has been diagnosed using such advanced technology.
Professor Krishna said: "I am very pleased that we have managed to contribute to the diagnosis of a terrible and completely neglected disease.
"We now want to use this information to develop tests that can be applied easily in areas where patients are actually suffering from this infection.
"Work on sequencing all the genes of the organism that causes sleeping sickness, supported by the Wellcome Trust, will undoubtedly help us in this objective."
The tsetse fly spreads the disease
The test has been developed to detect the Trypanosoma brucei gambiensi variant of sleeping sickness, which is found in west Africa and causes a delayed chronic illness that can last years.
Symptoms start with fever, headache, joint pain and once the parasites crosses the blood brain barrier, characteristic neurological symptoms and signs present; altered mental state, irritability, sensory disturbances, and co-ordination problems.
However, the practicalities of using the technique are being questioned from an economical as well as a medical perspective.
Simon Croft, professor of parasytology at the London School of Hygiene and Tropical Medicine, is sceptical.
He said: "There's urgent need for a much improved diagnostic test, not just one that tells you if you have the disease, but one that could be used during treatment, to see if it is working properly.
"This is a high-tech solution which is not applicable in its current form because of the technology and equipment required.
"It needs a bit more research. It is interesting, but there is a long way to go."
Professor Krishna and his team worked in collaboration with Angolan Doctors and the University of Wurzburg in Germany.
Professor Krishna says his discovery may be useful in the detection of other serious diseases.
He said: "The same approach could, equally, be used to improve the diagnostic accuracy of other infections, such as tuberculosis, which can be difficult to detect using conventional tests".