I well remember the moment when I myself was struck by this fear. It was in Lusaka, in November 1987. I was staying at the Ridgeway Hotel. I'd just driven there from Kabompo where I was living at the time, high up towards Zambia 's north-western border with Angola. I was on my way to Europe. The flight was going to leave the following day. I was dirty and tired after the long journey and had checked into the Ridgeway. That evening, after dinner, I went for a walk around the hotel and its grounds. At one end of the hotel I discovered the entrance to a casino. I took a look inside the dimly lit room and was immediately solicited by several prostitutes who were stationed along the wall next to the roulette table. Young and pretty. Dangerous. I thought at once that several of them were bound to be infected. How many men in my situation, visitors to the hotel or the casino, would succumb to the temptation offered by the girls? A night in the hotel, then goodbye. But death would be there already, inside their skin, sowed into their blood, flowing through their veins.

I drew back in alarm. There before me, a smiling mask, was death. The virus I was so afraid of. The girls were indeed young and pretty, but what they were offering me was death. I would have to be an idiot to accept. And, what is more, be willing to pay for it.

The fear, irrational though it was, stayed with me for many years, certainly until the mid-1990s. Perhaps it is still there, even if my fits of baseless anxiety have become increasingly rare. I took a test once, even though I had absolutely no reason to be scared. But scared I was, no matter what. And, I know, many others, very many, have experienced that same fear.

It was in Zambia too that I first encountered someone who quite definitely did have Aids. It was a young man. He staggered from an overcrowded bus in Kabompo. He fell at the feet of the people who had come to meet him. He was taken to the hospital in a wheelbarrow. He was as thin as it is possible to be.

Two days later he was dead. He had only just made it home from Kitwe, back to his mother in order to die close to her. His name was Richard. He was 17, and he was not gay. This was in 1988.

At the same place, Kabompo, I listened to a Dutch doctor giving a talk about this terrifying disease. It was an evening in the rainy season. The roads were a sea of mud, but people came from all points of the compass and a number of tribal chieftains were there. The premises belonged to one of the missionary groups and were the biggest in Kabompo, but still the place was packed to the rafters. There were others standing outside, looking in through the open windows. It was unbearably hot.

The doctor described in simple, straightforward terms – and what he said was translated into the local language by an interpreter – what happened in the body once HIV had entered the blood. He said that promiscuity was the principal culprit in the spread of the disease, and there was a rising hum, like a swarm of bees, from the women present. It was a pregnant moment. When the doctor had finished, one of the chieftains, a very old man, rose to his feet. He said: "We must all protect ourselves. For the sake of our children. There must be a stop to all unnecessary travelling. Families must stick together. Men must remain faithful to their women, women to their men. If not, we shall all die."

That was in 1988, during the rainy season. I often wonder how many of those who were there listening to the Dutch doctor were already infected. And how many of them are still alive today.

The mist is dispersing. I stare out to sea and I think about Aida and her mango plant. As she showed me it, I felt no doubt that it was one of the moments I shall remember for as long as I live.

Just how it came about, I don't know. Nor do I know when Aida made up her mind to take me into her confidence and share her secret with me. But I saw it the second time I visited her and her family.

The first time I met her, it was a very hot day. We left Kampala early so as to avoid being stuck in the chaotic traffic that envelops the city's roads every morning. Beatrice, who was the person helping me to make contact with people carrying the disease and writing memory books, had told Christine that I would be coming. At that time I didn't know Christine had a daughter called Aida. In fact, I knew only two things about Christine: that she had Aids, and that she was prepared to talk to me about it.

When we left Kampala that morning I felt the same distaste I'd been feeling ever since arriving in Uganda. There was something almost obscene about asking fatally ill people to talk about their suffering and their fate with a complete stranger. Somebody who, to make matters worse, had flown in from a distant corner of the world – Europe, the West – in which the terrible disease had almost been tamed and turned into a chronic but not necessarily fatal disease. The same disease that now is killing indiscriminately the length and breadth of the African continent and in other parts of the Third World.

I had slept badly because I had been worrying about the task ahead. My unease was not difficult to understand. I was dreading it because I knew I would find the fate of Christine and the rest of them very hard to take.

Beatrice had given us very efficient directions as to how to get there. We turned off the main road and, as always in Africa, we immediately found ourselves deep in a different world, a world usually, but wrongly, called the real Africa. Africa is always "real", whether it be savannah or slum, old ramshackle urban district or a grim and difficult-to-pin-down shadowland between bush and desert.

Christine had two houses. In one of them lived her mother and father and some of her brothers and sisters. When I arrived and got out of the car, the first thing I saw was her father, who was sitting peeling some kind of vegetable I had never seen before. He was unshaven but very dignified. Eventually I discovered that he was about 80, although nobody could be sure exactly how old. He had a keen eye, and was surrounded by an aura that immediately captivated anyone who approached him.

He went on peeling his vegetables all the time I was talking to Christine. Occasionally some child or perhaps his wife or one of the other women would give him something to drink.

He was like a measurer of time who would reject a normal clock with scorn. For him, a better way of measuring progress in his life and that of others was peeling vegetables.

Christine was thin and tired. I could see at once that she had put herself out in anticipation of our meeting. Her choice of clothes, her face carefully made-up, her meticulously brushed hair. She was typical of all the people suffering from Aids whom I met during my visit to Uganda: the last thing they were forced to surrender was their dignity. That was the ditch that had to be defended at all costs: after that there was nothing but death, and it often struck quickly once their dignity had been lost.

Christine said:"I have a daughter."

We were sitting on two brown stools behind the open but covered room which the family used to prepare food. Christine said something in her native tongue. Her daughter emerged from a clump of banana trees. She was wearing a dark blue skirt, which was ragged and torn, a red blouse, and she was barefooted. She was slim and tall and took after her mother: they had the same features around their mouths and noses and eyes. Aida was shy, she spoke in a low voice and her eyes were cast down. When I shook her hand, she withdrew it as quickly as she could.