Between plantations of bananas, mangoes and avocados, a small group of men trek along paths freshly carved out by the November rains on a mission to inform and educate in an area of western Kenya where AIDS remains rife.

In Homa Bay, a remote rural region on the southern shores of Lake Victoria, AIDS is a major problem with studies showing that one in four people are HIV-positive.

Every day, a team from the medical charity Doctors Without Borders (MSF) led by Patrick Kibira Ochoro heads out on foot to reach the most isolated areas, going door-to-door in a bid to discuss, persuade and ultimately convince people to get tested.

"For a lot of people here, HIV is not really an issue to them. For them, the number one priority is food, water," Kibira explained.

"That's why we talk to them, to ensure that they understand why it's important for them to go testing, at least once a year."

The number of new HIV infections worldwide may have fallen by 35 percent over the past 15 years, UN figures show, but the fight against AIDS is far from over in this rural western area.

MSF is currently focusing its efforts on Homa Bay's Ndhiwa district after conducting research there in 2012 that showed some very worrying statistics.

Figures from the study showed an HIV prevalence of 24.1 percent -- meaning one person in every four was HIV-positive -- compared to the national average of 5.5 percent. And the rate of new infections stood at 2.0 percent, compared with the national average of 0.25 percent.

And the research showed 41 percent of people affected have no idea that they are HIV-positive.

In the light of the alarming statistics, MSF changed its approach and started reaching out to people rather than waiting for them to come to the charity for help.

- Tackling cultural norms -

There are a number of socio-cultural reasons why people in the area are more affected than others.

Here the practice of "jaboya" is commonplace whereby sexual favours are traded for fish. Prostitution is also widespread.

And the tradition of "wife inheritance" whereby a man marries a newly-widowed woman within his family is also common practice among the Luo people who live in the area.

Before marrying a new husband, a woman is required to have sex in order to "purify" herself from her previous marriage.

Lillian Atieno Ochola, 37, became HIV-positive 14 years ago after she was "inherited", with the virus passed on to her by her second husband. She then passed it on to her son through breastfeeding before realising she was infected.

Since then, she has been trying to warn her neighbours of the dangers.

"I'm urging other fellows not to get into such kind of inheritance before being tested," she said, saying that people generally "respond well and some use the advice and get tested."

The Luo, Kenya's third largest ethnic group, also practise polygamy. And even if it is not openly acknowledged, men often continue to keep lovers hidden away.

The Luo also reject the tradition of circumcision, a practice recommended by the World Health Organization (WHO) which can reduce the risks of contracting HIV among heterosexual men by 60 percent, studies have shown.

Although treatment is widely available in Kenya -- UN figures show that in 2011, 72 percent of those diagnosed as HIV-positive were being treated with anti-retroviral therapy -- there are still many other obstacles to overcome.

"Today, many of the challenges in combating HIV are socio-economic and cultural rather than bio-medical," said Lawrence Oteng, minister of health in Homa Bay county.

- Reaching the men -

One of the biggest problems is the stigma surrounding those diagnosed with AIDS.

Many are forced to hide their condition and sometimes end up not following their treatment properly.

"We are still fighting stigma," Oteng said.

Accompanied by a village elder, the MSF team arrives at a first house. There they engage in a long drawn-out discussion with a woman, who eventually agrees that her children be tested after admitting that she herself is HIV-positive and undergoing anti-retroviral therapy.

"We try to promote a family-centred approach, that involves them as a family," said Kibira.

"It's not easy. Some refuse, some become hostile, but if the counselling is good, they usually are very supportive."

Later another man is also persuaded to allow his children to be tested, but refuses to undergo the same test himself.

"The main challenge is getting the men," he said. "A lot of them don't want to be tested."

Explaining how circumcision can help is also difficult.

In Luo culture, sex is seen as a boost to the planting and harvesting of the land, and the idea of having to give it up -- even if only for time taken to heal after circumcision -- was initially seen in a negative light.

"When the VMC (voluntary male circumcision) started in 2008 or 2009, there was a big resistance from the Luo community," he said. "Circumcision at the time was very low. Now it is steady."

And with the younger generation less attached to such cultural ideas, they could eventually come around, he added.

Since MSF's door-to-door campaign began in August, some 5,200 people have been tested. And the NGO has set up mobile clinics where people can come to be tested or even circumcised.