Libreville (AFP) - In Gabon, they're called "sexually transmitted grades" -- when university teachers use the threat of giving low marks in order to coerce female students into providing sexual favours.

"He started coming on to me. I began refusing him, refusing and refusing... until the day when he gave me zero for my main piece of work," Melanie told AFP, speaking on condition of using a pseudonym.

Another student said that she was forced to switch courses after she rejected the advances of a teacher who had "made my life hell."

Like many people around the world, female students at Libreville's Omar Bongo university have followed the saga of sexual harassment surrounding Hollywood mogul Harvey Weinstein.

These young women may lack the media draw of glamorous actresses who are stepping into the TV lights -- but they have tales of male power and sexual intimidation that are hauntingly familiar.

Sexual coercion at university and high schools has for decades fed the "kongossa", as the rumour mill is known in this central African state.

But they rarely make the public eye.

Student leader Franck Matoundou said he had brought the problem of sexual predation to the attention of the educational authorities.

Responding to AFP, university administrative staff point to the difficulty of clearly proving cases of sexual harassment by teachers.

They also argue that students should lodge formal complaints through their department heads.

"If there is incontestable proof that a teacher is guilty, that person must answer for their actions," a spokesman for the ministry of higher education.

"If this really happens, it is unacceptable and the government condemns such behaviour," the official added.

Gabonese law provides for charges of sexual harassment by "any person occupying a hierarchical post" and President Ali Bongo himself has denounced a problem "that is growing in scale and which demotivates competent people."

Yet not a single teacher has been tried over the sex-for-grades bribery, according to official sources including the state prosecutor.

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"I understand it if people don't dare to file a complaint," said a teacher, aware that students fear reprisals and complicity among educational staff.

- Gossip -

Valery Mimba, head of the Iberian Studies department, says the problem of sexual harassment "does exist," although hearsay and scandal-mongering make it hard to assess the scale of the phenomenon and deal with it.

"When you want to give better grades to certain students, people will immediately think they have slept with the teacher," he says.

Some academics also say the teaching staff are also exposed to sexual blackmail from students in exchange for good grades.

"Somebody offered to sleep with me to raise her average mark," a departmental head told AFP, asking not to be named.

Another teacher said he turned down a bribe of 150,000 CFA francs (about 230 euros / $270) from a student wanting to obtain a master's degree.

Stigma and taboo provide fertile grounds in which both sexual harassment and rumours thrive in Gabon's higher education.

Some activists are calling for a specialised channel to put in place that would help to break the silence and let victims speak out.

"Proposals from students are welcome," said the representative of the ministry of higher education, adding that the only reason for inaction has been the absence of tangible evidence.

Beyond the walls of the university campus, sexual pressure and taboo are entrenched in business and other parts of Gabonese life, notes Matandou critically.

"Using women is a way for a man to assert his virility and flaunt his social success," he says.

Even so, legal progress is being made -- and "women are more conscious of their rights" and fight for them, insists an expert who has closely followed the country's struggle with gender inequality.

A law on sexual harassment entered the statute books last year, the definition of adultery has been broadened to include men, criminal law has been changed to widen the definition of rape and widows have the right to inherit their husband's wealth.

"Efforts are still needed, there is no equality, but this is not a fight that is limited to Gabon but applies to the entire world," the source said. "In every society, women have always been marginalised."