Lebogang Motsumi, 27, still remembers the moment when she learnt she had contracted HIV from a man a decade her senior.

"It was August 15, 2009, at 1:00pm," she said, recalling the instant when her life changed traumatically.

"I was so ignorant," she said. "I thought HIV had a face" -- thin, poor and dying -- "and I wasn't that face."

The man who infected her with the AIDS virus was a "sugar daddy" or, in local parlance, a "blesser" -- an older man who "blesses" a younger, often poorer girl with money and gifts and expects sex in return.

The danger of the "blessers" has been in the spotlight at the International AIDS Conference in Durban this week.

In South Africa, seven million people live with HIV -- and older men are thought to be largely to blame for the shockingly high rate of infections among teenage girls and young women.

"To the 'blessers', there is only one level I want: the zero level, zero tolerance for men who put adolescent girls at risk for HIV," UNAIDS chief Michel Sidibe declared on Monday at the conference's opening session.

Every week, an estimated 2,000 South African women between the ages of 15 and 24 contract HIV.

Girls between the ages of 15 and 19 are up to eight times more likely to be HIV-positive than boys the same age.

Age-gap relationships are the engine driving the HIV epidemic in sub-Saharan Africa, explained Professor Salim Abdool Karim, director of the Centre for the AIDS Programme of Research in South Africa (CAPRISA).

- 'He's in control' -

The programme examined the genetic sequences of the HIV virus in a community in the KwaZulu-Natal province -- the hotbed of South Africa's epidemic -- to track how it was being spread.

The results revealed a cycle of infection.

"Over three out of every five young women -- teenagers and women in their very early 20s -- acquired HIV from a man around his thirties, about eight to 10 years older," Abdool Karim told AFP.

The skewed power dynamics in these relationships make it difficult for the young women to demand safe sex, increasing their chances of contracting the virus.

"You don't even want to talk condoms, or the guy will think you're being promiscuous," said Motsumi, who was 17 when she started going out with her older partner.

"You know you should, but he's in control of the sex: when you have it, how you have it."

It was a problem made worse by parents and nurses more intent on delivering moral lectures than helping her make informed decisions, she said.

As infected young women grow older and reach their thirties, they infect the next group of men "who then infect the next group of young women, and so it goes round and round," said Abdool Karim.

"Blessers" has overtaken "sugar daddies" as the common term in South Africa, emerging from the widely�used "blessed" hashtag on social media posts and photographs.

- Talk about sex -

"It's transactional, not love," said Motsumi who, after a string of such relationships, is sharing her experiences at the Durban conference.

"I wanted the money, I wanted to fit in, wear the latest sneakers like my friends."

The South African government is straight-forward about the problem.

Last month, it launched an awareness programme, where Deputy President Cyril Ramaphosa chanted: "Down with blessers! Down with sugar daddies!"

Health Minister Aaron Motsoaledi says it's time to shed taboos and start talking to young girls about sex.

"Every parent wants to believe that their daughter is an angel... (but) the fact that they are so highly infected it means they're having sex," he told AFP.

Bringing the alarming rates of infection down will take more than just talk.

"Blessers" thrive on poverty -- and girls who stay in school and have a job are bound to find them less attractive.

"Can we give them skills and link them to economic opportunities to reduce their dependency? Because that's where the issue of sugar daddies come in," Motsoaledi told AFP.

In 2013, researchers in Britain and South Africa published the result of interviews with 3,500 teenagers, showing that by narrowing the poverty gap, "blessers" could be thwarted.

Teenage girls from households which received child support were two-thirds less likely to have a much older boyfriend compared to counterparts from homes that did not receive the benefit.

These girls were also half less likely to have sex in exchange for food, money or school fees.

Motsumi knows how she is going to approach the subject with her six-year-old daughter.

"I'll give her the information she needs to make good choices," she said.

"I can't enforce my morals, but if you want to date older men, you need to know the risks."