In early 2005, Wuilder Chanchabac, a 31-year-old who has the small stature and thick black hair typical of Guatemalans of Mayan ancestry, did what many young Central American and Mexican men and women do: He left home for the United States to earn a better living. Because U.S. work visas are hard to come by, Chanchabac followed friends and relatives who’d made the journey before him. He paid a guide, also called a coyote, to lead him through the obstacles along the way: Mexican immigration authorities, violent gangs, the treacherous currents of the Rio Grande and hawkeyed U.S. Border Patrol agents strategically positioned in the Texas desert scrubland. Not long after he arrived in a small town in Missouri, where two of his brothers awaited him and arranged a job at a poultry plant, Chanchabac met a Latina girl named Noemi, with whom he fell in love. But several months after he and Noemi first had sex, Chanchabac began to have persistent aches and fevers, and after several rounds of over-the-counter drugs failed to have any effect, his brothers took him to a hospital. There a blood test revealed that he was HIV positive.

“I was angry with myself,” said Chanchabac, speaking in Spanish, in a café in his steamy hometown of Tecún Umán, where palm and banana trees thrive and air-conditioning is a rare luxury. “It was a moment of panic, and I nearly drove myself crazy. The person who I never expected to have HIV gave it to me. I didn’t use protection with her because I never expected her to have it.”

When Chanchabac’s brothers learned of his condition, they told him they thought it would be best if he returned to Guatemala. They feared that if he sought health care in the United States, he might risk being deported, so he returned to his mother’s cramped house in Tecún Umán. She received him uneasily.

“At first she called me a dog and said I wasn’t worth anything,” he said. “But then once I went on treatment and started feeling better, she saw I was the same person I had always been.”

Chanchabac is now healthy and taking free antiretroviral drugs provided by Doctors Without Borders. He has also been counseled by a local nongovernmental organization (NGO) called Educavida about not putting others at risk. “I only use protection now,” he said. “I don’t want to infect anyone.”

HIV/AIDS experts along the heavily trodden migratory corridor of Central America, Mexico and the U.S. are increasingly concerned about a new group of people like Chanchabac: migrants traveling to the United States who become infected along the way or, more often, when they reach the United States.

“We could have a major epidemic of HIV among migrants brewing,” said Jorge Saavedra, the HIV-positive director of Mexico’s National Center for the Prevention and Control of AIDS (CENSIDA). “The numbers are low now, but that could easily change.” CENSIDA and other research institutions have found that migrants have a greater number of sexual partners and are more likely to use illegal intravenous drugs than nonmigrants.

According to a 2000 study by Carlos Magis-Rodríguez, CENSIDA’s director of research, migrants’ transient lifestyles and exposure to U.S. culture can influence their sexual practices. Loneliness, isolation and a lack of women can also mean that male migrants have sex with male partners or with sex workers who are often intravenous-drug users.

Each country along the migratory route is refocusing prevention and care strategies on mobile populations, and there have been some efforts to coordinate tactics between countries. Mexico and Guatemala, on Mexico’s southern border, are just beginning to track HIV among returned migrants, and have become especially concerned about transmission in rural areas where HIV-positive migrants who are unaware of their status are infecting spouses.

Border towns, where commercial sex work and intravenous-drug use tend to be high, have also emerged as key sites of HIV transmission. On Mexico’s northern border, Ti-juana, across from San Diego, and Ciudad Juárez, across from El Paso, Texas, have seen steady increases in transmission among high-risk populations of intravenous-drug users and commercial sex workers who survive off the flow of drugs and people back and forth across the border. On Mexico’s southern border, outreach groups say sex workers and female migrants in particular are frequently coerced into having unprotected sex, putting them at risk.

In the United States, it is often assumed that immigrants bring diseases into the country, not leave with them. But the United States’ HIV rate is 0.6 percent—twice Mexico’s rate of 0.3 percent. And Guatemala’s HIV rate of 1.1 percent is nearly four times that of Mexico, though Guatemala has a far smaller population—12.7 million people—than that of Mexico, 108 million, and the United States, 301 million.

HIV transmission patterns among migrants vary from country to country, but U.S. immigration policy links them all and influences the movements and behavior of millions of people.

“When extreme poverty forces people to leave their homes in search of a way to feed their children, and the U.S. has good paying jobs available, people will go there, no matter how many walls or fences are erected,” said Father Ademar Barilli, a Brazilian priest who runs a shelter for migrants on the Guatemala-Mexico border. “But by not giving people a way to enter the country legally, the U.S. government is favoring family disintegration, and making people vulnerable to things like HIV.”

Other experts agree that the pressures particular to migrants introduce risks they might not otherwise encounter.

“When migrants leave home and go to the U.S., they find themselves in another reality,” said Saavedra. “They go alone and don’t have the social restrictions they had in their villages, and so they may behave differently. They also don’t have sufficient information about risks, which makes them vulnerable.”

For many migrants, the long journey to the United States begins not in Mexico but in Central America or even South America. And not all migrants who leave home actually reach the U.S.; for a variety of reasons, thousands end up stranded, clinging to a shaky existence in border towns. The need to survive and a lack of a support network often lead them to illegal or marginalized employment, such as commercial sex work. On Mexico’s southern border, more than 90 percent of commercial sex workers are from Honduras, El Salvador, Nicaragua and Guatemala, and it is estimated that they reside in the region an average of three or four months, depending on the working conditions and the demand for their services.

Faviola, who asked that her real name not be used, is a 33-year-old Honduran woman with freckles and corkscrew curls bobbing in a ponytail. In the charmless border town of Tapachula, in the state of Chiapas, she works as a “waitress,” a euphemism for “prostitute,” in bleak, tarp-covered cantinas. Faviola left her three children in Tegucigalpa, the capital city of Honduras, three years ago, intending to reach the United States and earn a better living to support them. But after crossing through El Salvador and Guatemala, she ran out of money in Tapachula and took the waitress job, not anticipating that it would stipulate sex. While she says that she uses protection nearly all the time with clientele, some will offer three to five times the regular fee of $30 to have unprotected sex.

“A lot of men don’t like to use protection,” she said. “I know they could be sick so I always try to use it.” Faviola says she dislikes her job but soldiers on to save money to send home to her children. “There’s nothing for me in Honduras,” she said.

Interviews with other sex workers and NGOs in Tapachula revealed that sex workers are frequently offered high sums for unprotected sex, and many, because of poverty and desperation, feel unable to refuse.

According to Rosember López, director of the Tapachula HIV outreach organization Una Mano Amigo (A Helping Hand), local authorities stigmatize commercial sex workers, mandating HIV testing, from which the city profits. But that mandatory testing means that women and girls who think they might be HIV positive are less likely to get tested because if they are found to be positive, the city will restrict them from working.

“It doesn’t help that nearly all of them are Central American immigrants within Mexico, which means they can’t get access to treatment through the government,” said López.

Una Mano Amigo also reaches out to migrant women passing through town. The migratory flows through Tapachula have decreased by more than 50 percent since Hurricane Stan in 2005 knocked out a cargo train route that was many migrants’ free ticket through most of Mexico. But on average, 80 to 100 Central American migrants still pass through the city’s shelters every day.

López says that many migrant women are raped during their journeys, while others are forced by coyotes, drivers, immigration officials or other authority figures to exchange sex for their passage north.

According to a 2004 report by the Pastoral de la Movilidad Humana in Guatemala, an estimated 60 percent of migrant women have some kind of sexual experience on their trip to the United States, from rape to coerced sex to sex with a traveling companion.

Barilli, the Brazilian priest in the Guatemalan border town of Tecún Umán, says that sometimes Mexicans perceive the Central American migrants as being responsible for bringing HIV into Mexico because countries like Guatemala, Belize and Honduras have higher HIV prevalence than Mexico.

“The fact is, most migrants come from small villages where HIV doesn’t exist,” said Barilli. “For them, in fact, the risk of HIV appears during their journey when they might be forced to have unprotected sex to get to where they want to go, or maybe they choose to have it when they arrive in the U.S.”

But while health experts see the southern border as an increasingly important way station for migrants and a critical place to reach and educate them before they make the journey north and face greater risks, it is largely overshadowed by the northern border.

“Most of the researchers focus on the northern border because it’s right next to the U.S., and so the southern border is really forgotten,” said Olivier LeTouze, director of Population Services International Mexico (PSI). “The northern border is the sales pitch for HIV prevention programs, because the threat is right here on the border. It’s easier to sell to U.S. funders, but that threat is in the south as well.”

The city of Tijuana, which also serves as a way station for thousands of migrants set on the American dream, has seen especially large increases in HIV prevalence recently. According to a 2006 study by researchers at the University of California San Diego’s (UCSD) School of Medicine, the number of men and women ages 15 to 49 infected with HIV in Tijuana may be as high as one in 125. Data in this study indicated that Tijuana’s HIV infection rate may be close to three times higher than Mexico’s national average and is driven primarily by
injection-drug use and the sex trade.

“One of the unintended consequences of border security is that people become more vulnerable to getting HIV through intravenous-drug use because fewer drugs are getting through to the U.S. and more are ending up in Mexican border towns,” said Stephanie Strathdee, an epidemiologist and chief of the division of International Health and Cross-Cultural Medicine at UCSD. Strathdee also noted that migrants and local female sex workers in Tijuana who have U.S. clients are at higher risk of contracting HIV than those who work only with the local population. Like the clientele in Tapachula, American and Mexican clients will pay a higher price for unprotected sex, she said.

Strathdee has also conducted research in Ciudad Juárez, across the border from El Paso, and has found similar links between injection-drug users, sex workers and HIV.

But even though some researchers near some of the biggest border cities have studied and identified trends and inspired new prevention programs in cities like Tijuana, other experts say much of the rest of the border is unexamined.

“We know what’s going on in Tijuana and Ciudad Juárez, and we know from our studies that IV-drug use is high in other border towns, but what about the rest of it?” said LeTouze of PSI. “Nobody’s looking at it.”

Saavedra of CENSIDA says he is surprised that the U.S. government is not investing more money in studying HIV transmission on the Mexican side of the U.S. border.

“It’s in the best interest of the U.S. to strengthen services on the Mexican side of the border because we don’t have sufficient clinics or services there, which means that people who need treatment will pay more and use services on the U.S. side,” Saavedra said. “There’s so much movement back and forth across the border in the border towns, it’s everyone’s problem.”

But of all the Mexican locations where HIV can potentially spread, Saavedra says, rural Mexican states with high migration rates are the most worrisome.

Two studies by the Mexico AIDS Initiative, a joint program coordinated by CENSIDA and the University of California Office of the President, found that 0.6 percent of Mexican migrants tested in California and 1.1 percent of adult rural migrants surveyed in Mexico were infected with HIV. The rate in rural Mexico was more than three times higher than the infection rate reported for the general Mexican population ages 15 to 49.

Mexican public health researchers have also become concerned about AIDS prevalence in rural women, particularly those who remain in Mexico while their spouses go to work temporarily in the U.S. The traditional feminine role in Mexico means few women are empowered to negotiate sexual practices with their migrant partners.

A 2007 study by Jennifer S. Hirsch, a professor of public health at Columbia University, in the American Journal of Public Health found that migrant husbands unfaithful to their wives were often at the highest risk of contracting HIV. That group was more likely to solicit sex workers while in the United States and less likely to have long-term relationships with other women.

CENSIDA has not collected data on how many migrant spouses have been infected with HIV, but Saavedra says the virus regularly appears in rural areas with high migration rates where the disease had not ever been seen. At the root of HIV transmission among migrants is the unstoppable movement of people, but experts say that undocumented or illegal immigrants are at greater risk than legal immigrants.

“The migrants who go without documents are the most vulnerable,” Magis-Rodríguez says. “They come from a different social stature, and in the rural areas where many of them come from, sexual education is very low.”

The Pew Hispanic Center estimates that each year since 1995, between 700,000 and 850,000 immigrants entered the United States illegally, bringing the total unauthorized migrant population to between 11.5 and 12 million. According to the Center, the total number of people believed to have evaded border security is between 6 and 7 million.

But even if diagnosed in the U.S. like Chanchabac, the Guatemalan, few are willing or able to seek care, and some never make it back to their countries of origin. A recent study found that 70 percent of patients diagnosed with AIDS at La Clinica del Pueblo, which serves Central American immigrants in Washington, DC, arrived at near-death stages of the disease.

Their mobility, migration patterns and lack of access to continuous health care also impede health service groups’ ability to reach them with prevention and care.

HIV status can also be a barrier for those immigrants seeking legal status. As part of the application process for legal permanent-resident status, immigrants must take a medical exam that includes an HIV test. Those who test positive cannot become lawful permanent residents unless they are granted a special HIV waiver from the U.S. government. According to the U.S. Centers for Disease Control and Prevention, the waivers are almost never granted.

Foreigners wishing to visit the United States are also asked if they have a communicable disease on visa applications, and those who are HIV positive are typically denied—a virtual travel ban on foreigners living with HIV/AIDS. The U.S. is one of the few countries to ban entry of visitors with HIV, a direct conflict with United Nations policy. In 2006, the Joint United Nations Programme on HIV/AIDS (UNAIDS) stated that there is “no public health rationale for restricting liberty of movement or choice of residence on the grounds of HIV status.”

“The ban is an ugly relic of the hysteria that has surrounded HIV/AIDS from the early days of the epidemic,” said Mark Kline, MD, president and chief retrovirologist at the Baylor International Pediatric AIDS Initiative at Texas Children’s Hospital. “Some of this may have been understandable early on—we knew very little about the virus and how it was transmitted. Now, more than two decades after the discovery of HIV, we know that an HIV-infected individual poses no risk whatsoever to casual contacts. It’s time the policy was updated to reflect the scientific facts.”

Meanwhile, the U.S. government has ramped up security to discourage undocumented crossings, and the Border Patrol’s apprehensions of illegal crossers declined in 2007. But many on the border say migrants will continue to cross illegally as long as extreme poverty in Latin America persists and jobs are available on the other side of the border. What’s more, health risks may only increase as the migratory process becomes more trying. “We’re trying to stop something where there’s a lot of desperation, need, hunger and hope,” said Tony Estrada, the sheriff of Santa Cruz County, on the Arizona border with Mexico. “[People’s] will is stronger than those barriers.”