Ancient killer: An Iraqi girl gets an injection for leishmaniasis (black fever)

The genetic codes of three deadly parasites have been unravelled by scientists, transforming the fight to contain diseases that kill and cripple millions each year in the developing world. The work promises the development of a new generation of drugs and vaccines for African sleeping sickness, Chagas disease and leishmaniasis, a family of insect-borne infections that are difficult or impossible to treat.

These “neglected diseases” kill at least 150,000 people a year, and leave millions more with brain, heart, kidney or liver damage. More than half a billion people ? or one in 12 of the earth’s population ? are at risk of contracting them, and they cause the annual loss of more than four million productive years of life. When they can be treated at all, the options are rarely effective and often unsafe. Melarsoprol, one of the main drugs used against sleeping sickness, is based on arsenic and kills one in 20 of the patients who take it.

The genome maps of the organisms that cause the conditions ? Trypanosoma brucei for sleeping sickness, Trypanosoma cruzi for Chagas disease and Leishmania major for leishmaniasis ? have given scientists genetic targets for improved drugs and vaccines, which could knock out the parasites without harming their human hosts.

Genome sequences of other pathogens also yielded such results. The malaria genome, for example, revealed that triclosan, an antibacterial agent used in toothpaste and mouthwash, could kill the parasite, and it is now beginning clinical trials as a drug. Scientists said they had already identified about 40 genes that appear in the parasites but not in humans, making them good therapeutic targets, though they said that it could be 10 years before drugs were ready to be tested on patients.

About 6,000 genes are also shared between all the parasites, raising the prospect of drugs that are effective against all three conditions.

The three genomes, details of which are published recently in Science, were mapped by a team of 238 researchers from 46 institutions in 25 countries. Much of the key sequencing work was conducted at the Wellcome Trust-Sanger Institute near Cambridge. Matt Berriman, who led the Sanger team, said: “To have the genome sequences of all three parasites is a unique opportunity to understand these diseases.

Comparing them, we can see how they are similar, what makes each tick and how they differ. “The catalogues of genes ? and hence the list of new drug targets ? are more reliable because we have the three sequences.”

Prof. Sanjeev Krishna of the St George’s, University of London, who researches sleeping sickness in Angola, said: “Treating sleeping sickness is like a form of medical Russian roulette, because you don’t know who will be saved or killed by the treatment available.

“Of course it shouldn’t be like that, and now we have completed this sequencing programme we can concentrate on finding the ‘magic bullet’ medicines that will help eradicate this disease.”

Sleeping sickness, which is transmitted by the tsetse fly, is endemic in 36 African countries. It kills an estimated 50,000 people each year, and 60million are at risk. The parasite causes fever and heart and kidney damage, and also disrupts sleeping patterns, so that sufferers struggle to sleep at night or to stay awake during the day. It can also cause brain damage, leaving victims in a “zombie-like state”, Krishna said.

Chagas disease infects between 16 million and 18 million people in South and Central America and Mexico, where it is carried by blood-sucking “assassin bugs”. It can lie dormant for up to 20 years before causing severe internal damage, usually to the heart.

Leishmaniasis is the most prevalent of the three diseases, affecting 88 countries in five continents, including southern Europe. It is carried by the phlebotomine fly, and about 12million people a year are infected. Its most serious form leads to anaemia and death.

Don Kennedy, Editor-in-Chief of Science, said the research was critical to the international development agenda agreed by the G8 summit in Gleneagles. “Tony Blair is obviously committed to doing something about the medical problems that make life in so many parts of the world so deeply fraught with peril,” he said. “This is a great start.”