The plight of Miriam Mbwana is a stark example of the tragedy being played out in millions of families across sub-Saharan Africa. Six of her 11 children have died of Aids.

Just as she might have imagined she could take life more slowly in her 60s, she faces the biggest challenge of her hard life: bringing up 28 orphaned grandchildren, all of whom are under 15 years old.

This was just one of the terrible stories, on one day in one hospital in Malawi, told by Kevin Toolis and Gideon Mendel in our special report in today's Guardian weekend to mark World Aids Day.

They present a deeply disturbing picture of a continent, its social and economic life shattered. Aids is likely to cut the gross domestic product of South Africa, one of the region's strongest economies, by 17% by 2010. Meanwhile, hopes for development have been crippled in many African countries where teachers, nurses and doctors are dying as fast as everyone else. We are only beginning to glimpse the implications for the political stability of the continent.

The cruelty of any disease is that it bears most heavily on the poor and the marginalised. This is particularly true of Aids. It is always among the socially excluded - sex workers, drug addicts - that the disease first thrives, as the shocking new statistics from the Russian federation published by the United Nations programme on HIV/Aids this week indicate; the number infected, most of them drug-users, has more than doubled there in just one year. Not only are the poor and socially excluded most likely to catch the disease, they also have the least resources with which to fight it. There is an enormous gulf between the treatment of HIV/Aids in the developed world and in the developing world. In the former, the disease can be con trolled with drugs, but in the latter it is a death sentence.

What the west urgently needs to address is how a handful of hugely profitable drug companies are still protecting their patents on the drugs which could save millions of lives. For example, fluconazale made by Pfizer is used for treating the infections to which many HIV/Aids sufferers are prone.

Pfizer, anxious to protect its lucrative patent, refuses to allow generic versions (which cost 29 cents a day compared to $12 a day) and instead, offers time-limited donations - dismissed by critics as nothing more than a public relations gimmick. Another crucial drug is neviraprine, which stops mother-to-baby transmission of HIV.

As contentious is the expensive combination antiretroviral therapy which has now been produced in generic versions in Brazil, Thailand and India. Today we report that Glaxo Wellcome has accused a drug distributor in Ghana of violating its patents by importing a generic version from India.

This is unacceptable. While it is true that drugs will never solve the crisis, they can ease it. The drug companies need to inject some urgency and sense of global responsibility into their negotiations with the poorest and worst affected countries.

Along with cheaper drugs, sub-Saharan Africa needs aid for its inadequate health services, which are swamped by the needs of the dying. And it needs aid for the biggest challenge of all: how to change a continent's sexual practices. The task is enormous, touching as it does on the most intimate relationship and the balance of power between men and women.

But it can be done: Uganda has shown that high-profile, honest prevention campaigns can slow the rate of infections. Miriam Mbwana's grandchildren don't have to die like their parents.