By Jonny Hogg
BBC News, Fort Dauphin
The lights of the bars in Fort Dauphin stay bright long after the rest of the countryside around has darkened.
Mineworkers and other foreign contractors mingle with local people to drink and dance in this remote part of Madagascar.
"Sure, there's prostitution here," says one South African mineworker, sitting at a table with three young Malagasy women. "With lots of single men away from their families, it's bound to happen."
Francesca, who works at one of the bars, is anxious about her health.
"I've had relationships with foreigners, but only for love. I am worried about sexually transmitted diseases," she says, talking over the loud music.
Recent government figures suggest Francesca may be right to be concerned.
According to the Ministry of Health, 30% of sexually active adults in Fort Dauphin could have syphilis. The symptoms of syphilis include genital lesions, which increase the risk of HIV transmission between sexual partners.
"Syphilis in itself is not a serious thing but if we don't control levels of syphilis in Fort Dauphin then we'll get into real problems with HIV," says Fenosoa Ratsimanetrimanana, head of Madagascar's National Committee to Fight HIV/Aids.
Although syphilis can be easily treated in as little as three days, Mr Ratsimanetrimanana says that the disease could allow HIV finally to gain a foothold on the Indian Ocean island.
For this reason, the government has decided to declare a state of emergency in the town.
Fort Dauphin lies on the southern tip of Madagascar, hemmed in by mountains. Until a few years ago it was one of the most isolated and unchanged spots in Madagascar.
But Fort Dauphin is now the focal point for QMM, a Rio Tinto mining project which is investing at least $600m into Madagascar to mine ilmenite near the town.
Foreign workers have flooded in, causing a business boom in the town.
"Prices have tripled since 2006," says Francesca. "Sometimes the price of tomatoes can go up in just three days."
There are reports that some hotels are booked out for three years, to cope with accommodation demands from the expatriate workers.
This economic explosion is also attracting sex workers from across the country.
"There are more foreigners with more money to spend on prostitutes, so prostitutes from all over the country are coming here to work," says Emanuel Haro, the regional development director for Fort Dauphin.
There are an influx of foreigners to Fort Dauphin
QMM President Gary O'Brian insists his company takes precautions against the spread of sexually transmitted diseases.
"We do have HIV-positive workers in Fort Dauphin but we monitor them carefully," he says.
"We have a code of conduct in place which deals with fraternising with the locals. I can confidently say that we've done everything we can to make sure we're not having a negative impact on the rates of sexually transmitted infections there."
But are these rules being obeyed?
Another South African mineworker told me he believes he has seen "a rise in prostitution".
"If it's reported we get sent home, but the problem is no one reports, it so it goes on," he says.
Madagascar has some of the highest rates of sexually transmitted diseases in the world. However, HIV infection rates for the country remain low, under 1%.
"We don't know why we have such low HIV rates compared to mainland Africa. Some have called this the Madagascar paradox," says Mr Ratsimanetrimanana.
"We don't understand but we thank God for this, we are very lucky."
But there are also worries that Malagasy attitudes to sex are leaving the door open to an Aids epidemic.
"When young Malagasy hang out, they like to drink some beer and sleep with prostitutes. Some people use condoms, but some don't," says Rock, a young Malagasy man living in Fort Dauphin.
Lydia, a young woman working as a shopkeeper in Fort Dauphin, agrees.
"In cities maybe people use condoms but in the countryside people don't like them. Also, some foreigners don't like to use protection when they sleep with the Malagasy girls."
The combination of economic boom and relaxed sexual attitudes appears to be driving up rates of syphilis and could be creating an HIV time bomb in Fort Dauphin.
In answer to this the government is launching a thorough sex education programme.
For some people in Fort Dauphin it will be the first time.
"I've never had any sex education," says Francesca, "I'm scared for myself and I'm scared for Madagascar. HIV/Aids could be very bad for our future."