They are rolling works of art, brightening dreary stretches of highway, hauling everything from textiles to fruit to people. The brilliant colors and intricate adornments of Pakistan’s trucks have been part of the national landscape for nearly a century.

Behind the tinkling bells that line the trucks’ windshields is a little-discussed and even taboo element of Pakistani culture: The long-distance drivers, who spend lonely hours on the roads connecting major cities and ports, are considered an at-risk group for HIV infection. Health advocates say the truckers frequent prostitutes, male and female, and engage in other unsafe practices.

Truck art was recently enlisted for an awareness-raising exhibit in Islamabad aimed at helping to prevent HIV and AIDS. A nonprofit advocacy network called AMAL (“action” in Urdu), with support from the Australian government, surveyed drivers and shared the findings with truck artists who conceived images to depict the men’s lives.

The prevalence of HIV among intravenous drug users, sex workers, migrant workers and truck drivers continues to rise in Pakistan, officials say. Intravenous drug users have the highest infection rate, at more than 30 percent. Truckers have a much lower incidence of infection — but because same-sex relationships are forbidden in Islam, the drivers are a difficult group to reach and counsel.

For each truck, there are a driver and two cleaners who work together, explained Ali Razique, a physician who heads the National AIDS Control Program at the National Institute of Health in Islamabad. The cleaners are “cute, young, smart boys,” who can travel freely with the drivers where women cannot, he said, and often they are also sexual partners.

“This behavior exists everywhere, all over the world, even in Pakistan,” said Razique. “But people are not very open about it. It is seen as un-Islamic, but the behaviors are there — and the more information we provide to people, the more people get tested.” Many of his patients confessed they didn’t know they could get tested and they didn’t know HIV and AIDS are treatable.

“There is a perception about homosexuality among the drivers, but I do not agree with it totally,” said truck driver Mohammad Ashraf Khan. The 56-year-old from Peshawar has been driving for 22 years and said he has a hard time believing that after a long day of driving, a trucker would be interested in anything other than finding a place to sleep.

“But, yes,” he concedes, “when the drivers spend more than a day at one station then he may be involved in sexual activities.”

Another truck driver in his early 50s said it is “socially safe” for men to partner with other men because no one asks questions. Citing social pressure, he requested that he not be identified.

If a driver is found with a woman, everyone grows suspicious, he said, but that is not the case with male prostitutes or colleagues. The driver used to visit brothels on the highways in Punjab and Sindh provinces in the 1980s, under Mohammed Zia ul-Haq’s military rule, but these days, he said, it’s hard to find such places.

“I am aware of HIV now, but I never attempted to do a screening out of fear of testing positive,” he said.

HIV treatment centers are mostly found in cities, yet many of the at-risk truck drivers and migrant workers come from Pakistan’s unstable tribal belt and Khyber Pakhtunkhwa province in the northwest, where resources are already stretched to the limit to combat Islamic militancy and terrorism.

A recent survey of HIV-positive patients in Khyber Pakhtunkhwa, the Federally Administered Tribal Areas and a portion of Afghanistan found that, of 1,013 registered patients in one clinic, 189 of them were in the driving profession.

The number of reported cases has been on the rise, said Hilal Ahmad, a counselor at the center. In 2008, 11 cases on average were reported per month; that number has increased to 19 new cases per month in 2012, he said.

But Ahmad sees one upside in those increased numbers: “It’s very encouraging that now people are reporting and coming to get treatment.”

Haq Nawaz Khan in Peshawar contributed to this report.