Ashton Kutcher, Ryan Seacrest and other Hollywood celebrities have also joined the Twitter campaign. Starting on Wednesday, the participants will send out tweets encouraging the public to donate to buy bednets which guard against the mosquitoes that spread malaria in Africa.

Gates will also take part in TV charity fundraiser Idol Gives Back on Wednesday to promote the fight against malaria and other health causes.

Organizers of the Twitter fund-raising push are working with the United Nations Special Envoy for Malaria, Ray Chambers.

It's one of the few campaigns I'm aware of where $10 buys a bednet which can save a child's life, Chambers told Reuters. The tangible feel of it is greater than any other campaign I've been exposed to.

Malaria causes more than 1 million deaths annually worldwide, but the problem is most acute in Africa.

The UN aims to reduce the deaths from malaria to near zero in Africa by 2015. So far, more than $4 billion has been raised to fight the disease, mostly from the World Bank, government agencies and the Bill and Melinda Gates Foundation.

The UN expects to cover 800 million people at risk of malaria with bednets, but it is still short of funding for roughly 50 million of those nets, Chambers said.

On Wednesday, singing contest American Idol, the top-rated program on U.S. television, holds its Idol Gives Back show. That too will ask for public donations for malaria relief, as well as charities working with children and poverty in the United States.

Idol Gives Back is supported by News Corp, Ford Motor Co, Exxon Mobil Corp, AT&T Inc and Coca-Cola Co.

Others taking part in the Twitter campaign include basketball star Shaquille O'Neal, talk show host Larry King, singer Jordin Sparks and Sarah Brown, the wife of British Prime Minister Gordon Brown, organizers said.

Collectively, the participants have 50 million followers on social networking site Twitter.

Organizers said it was unclear how much money will be raised through the campaign, which was inspired by a race a year ago between actor Kutcher and news outlet CNN to be the first to reach 1 million followers on Twitter.

After Kutcher won the contest, he donated $100,000 to Malaria No More, which is one of the groups that will benefit from this latest Twitter campaign.

This year, the Case Foundation will match up to $25,000 of the donations made through the campaign.

It's matched by real funding that's going to buy real nets for real people, said Biz Stone, co-founder of Twitter, who will also be one of the figures sending out tweets.

It goes all the way from one little tweet to a real physical manifestation of change, he said.

This first blast of messages over Twitter will end on Sunday, which is World Malaria Day. It will be followed later in the year by more tweets from the participants.

Medicine Twitter