What do you do with your money if you are the richest man in the world? Go to Africa and find a cure for a killer disease, Bill Gates decided yesterday.

The founder of Microsoft travelled to rural Mozambique to announce the donation of £100m ($168m) to fight malaria, ushering in what some call a new era of philanthropy.

He almost doubled what the rest of the world - governments, the UN and charities - spend on a disease that kills a million people every year, 90% of them in Africa.

Some of the money will accelerate research on new malaria prevention and new drugs to fight drug-resistant strains of the disease. Most of it will go into a quest for a vaccine which, if successful, could transform the continent.

"It is time to treat Africa's malaria epidemic like the crisis it is," Mr Gates said. "It is unacceptable that 3,000 African children die every day from a largely preventable and treatable disease."

The World Health Organisation and the government of Mozambique hailed the donation as a humanitarian gesture that partly filled a huge gap in funding for malaria research.

Malaria is a parasitic disease, transmitted by mosquitos, of which the most deadly, Plasmodium falciparum, is the most common in Africa. Inside the body the parasite infects the liver and red blood cells, impairing the blood flow to vital organs. In homes and clinics across the continent the pale, shivering sufferers of the disease can be seen.

Perhaps it was a coincidence, but the announcement came just days after Forbes Magazine published a rich list topped for the 10th consecutive year by Mr Gates and his £28bn fortune.

The 47-year-old chairman and co-founder of the computer software group is up £1.8bn from last year because of the improvement in the share price of dotcom stocks, keeping him in a plutocratic class of his own.

After initial criticism that he was hoarding, Mr Gates has promised to give away all his wealth, bar a few million dollars for his two children, before he dies.

The Bill and Melinda Gates Foundation, which he runs with his wife, overtook the London-based Welcome Foundation several years ago as the world's biggest charitable foundation, with assets of £14bn. It has already spent more than £1.9bn on various health projects in developing countries.

Unlike many American foundations, the Gates one doles out a hefty proportion of its assets and takes care to back worthy, useful causes, said Stacey Palmer, editor of Chronicle of Philanthropy, a newspaper of the non-profit world.

Its headquarters is an anonymous, unmarked two-story building in Seattle with a staff of about 100 to manage a budget greater than the GDP of many countries.

The foundation paid for dozens of journalists to accompany Mr and Mrs Gates for a tightly managed media event. It was partly an attempt to polish their image, but also a shrewd use of the media to highlight a neglected issue, said Ms Palmer.

"There's got to be an element of wanting good publicity, but Bill and Melinda Gates come across as sincere," she said. In absolute terms, their foundation had surpassed the likes of Rockefeller and Carnegie.

Mr Gates is fascinated with biology and scientific advances such as mapping the genome of the mosquito, believing that the insights can benefit the poor and sick.

Today he will meet Nelson Mandela in Johannesburg to discuss combating HIV/Aids, followed by a trip to Botswana tomorrow to visit Aids clinics and research projects. But malaria is his best chance to do good, he believes, because the funding for the fight against it is so low. Speaking at a malaria clinic in Manhica, a dusty village some 50 miles north of the Mozambique's capital, Maputo, he said the money would be divided into three grants.

Some £17m will go over five years for research on a new prevention strategy to use existing drugs to protect infants from the disease; £24m will go over five years to the Medicine for Malaria venture, a Geneva-based public-private partnership to develop new drugs to replace those to which mosquitoes have become resistant; and £61m will go over four years to the Seattle-based Malaria Vaccine Initiative, which believes a vaccine is possible because some people become naturally immune.

Some scientists say an effective vaccine may never materialise and that the funds would be better spent on basic things such as insecticide-treated nets and sprays to control mosquitoes. But Mr Gates was upbeat. Like polio and smallpox, malaria could be conquered, he said.

Sebastial Matusse, 40, watching the Gates cavalcade as she queued outside a clinic, could only hope he was right. Malaria has caused her to have two miscarriages, claimed the lives of two infant children, and was yesterday afflicting for the seventh time her son Sebastio, five, who shivered in a blanket in her arms.

Two dozen mothers and children missed church to meet what clinic officials told them was a white man who wanted to help.

Seated under a corrugated tin roof, they gazed at the couple sitting cross-legged on the reed mats and tried to ignore the phalanx of TV cameras and photographers.

Mr Gates held Galia Machava, a four-month-old who was too busy playing with the hem of her pink dress to appreciate the symbolism - the richest of the rich cradling the poorest of the poor.

Africa bears brunt of mosquito-borne peril

· Every year 300 million-500 million people are infected with malaria. One million die - 90% of them in Africa

·Malaria kills 3,000 African children every day and is the leading cause of death among children in Africa

· The disease is spreading so rapidly in Africa because of the growth in resistance to standard anti-malaria drugs, such as chloroquine

·Malaria costs Africa an estimated £7.3bn in lost GDP

·Strategies used to combat the disease include insecticide-treated nets, drugs, and sprays to control mosquitoes

· Current spending on local malaria control is £120m a year. But scientists say £900m to £1.5bn is needed

· Malaria consumes 40% of public health spending in Africa and accounts for up to half of inpatient admissions and outpatient visits in the worst-affected areas

· Malaria is responsible for 24% of all hospital deaths and 44% of outpatient hospital visits in Mozambique