By Jane Elliott
BBC News health reporter
Over the last four decades Don McCullin has been to the world's most troubled areas and photographed harrowing scenes of death and destruction.
His iconic pictures chart the wars in Vietnam, the Congo, Biafra, Cambodia, Bangladesh, El Salvador, and the Middle East, including the June 1967 Six Day War.
But despite all the bloody conflicts he has witnessed he is haunted by images from his recent trips to Africa with Christian Aid to record how the continent has been affected by the HIV/Aids pandemic.
Four years ago he went to Zambia, South Africa and Botswana to document the lives of people living in desperate poverty. These photographs were exhibited in his exhibition "Cold Heaven".
This year he retraced his steps to Zambia and South Africa to see what impact antiretroviral treatment (ART) for HIV is having and to try and track down the people he originally photographed.
He found almost unbearable tragedy - but also examples of people rising above the pain and misery of their situation.
"There is no end to the amount of pain you can find in Africa. I feel there will be pain and suffering on this continent for at least the next fifty years. You see mile after mile of shanty town it is terrible.
"You see people who cannot contain their bowels and you smell them lying in their huts dying.
"One part of the world should not be suffering like this."
He said that as a new father seeing the children suffering had been particularly painful.
"I went into a hospice and they had 30 babies aged from about nine months and they had tumours around their eyes. I just cannot bear to think about it."
When he retraced one family he found the mother had died after her shack burnt down with her and some of her children inside.
He was able to show the remaining family the pictures he had previously taken.
"When I took them the photos I had taken on my previous visit the husband looked at them and just smiled. He then gave them to his son who took them into the back of where they were living and just cried."
In South Africa he found two of his previous subjects receiving ART, which is free in the country, and doing well, but in Zambia he found a different story. The drugs here cost £6 a month and are too expensive for most Zambians.
He said his brief from Christian Aid had been to record a story and to ensure that the images were subtle and not too shocking.
"There is a problem with the atrocity pictures. People are looking for something more glamorous and they do not want to see these kind of pictures and you can't blame them.
"But at the same time what we are trying to do is bring awareness. We have to do it in a more subtle way.
"And you can do it without poking a finger is somebody's eyes".
Judith Melby of Christian Aid said the exhibition showed there was some hope for the people of Africa.
"Don McCullin's exhibition is extremely important for us. His photographs illustrate the depth of the misery caused by this devastating epidemic.
"But there are also rays of hope as seen in photos of the people on antiretrovirals - they are leading productive lives and bringing up their children.
"All these drug therapy programmes must be provided in tandem with intensive community support and measures to alleviate poverty.
"Unless we address the root causes of poverty by cancelling the overwhelming debt owned by these countries to the wealthy nations and change the trade rules which blatantly favour rich countries, it will be even more difficult to bring HIV under control. These photographs should strengthen our determination to end these injustices."
"Life Interrupted" opens at the County Hall Gallery, on London's South Bank on November 26, and will tour throughout the UK next year.