HIV is Sexist: Why it Infects Less Male Heterosexuals

Researchers have determined that biology, not just lifestyle, can heavily impact how readily HIV spreads from person to person. Males reportedly only receive very limited strains of the virus, but in-turn can spread that "fittest" strain to women or other men more easily.

Past surveys conducted by the World Health Organization (WHO) have revealed that women make up about half the world's HIV infected. The large majority of the other 50 percent consists of gay and bisexual men - referred to as men who have sex with men (MSM).

In the United States alone, it was also found that among the most recent HIV cases in women, a whopping 84 percent were infected as a result of heterosexual contact, according to the Centers for Disease Control and Prevention (CDC).

So why the disparity? It certainly doesn't seem fair that straight men are most likely to dodge this life-changing bullet.

A recent study conducted by investigators at Microsoft Research and the Zambia-Emory HIV Project has now revealed that the genetics of the virus itself have a lot to do with this.

The study, published in the journal Science, details how only the strongest of HIV strains tend to infect heterosexual men because the cellular defenses of the penis are tougher to break through, compared to the defenses of the vagina or anus.

These defenses filter and fight off weaker strains, leaving only the strongest HIV strains to infect male genitalia. Heterosexual women and MSM groups are then more likely to be exposed to the strongest strain, leading to higher infection rates.

"The average [strain] in the population is probably average because it works best, and we found that that is true," researcher Jonathan Carlson told NPR.

However, many experts know that viruses love to hide their weaknesses as strengths, and the same applies here. According to microbiology expert Manish Sagar, this research sheds light on a new strategy to prevent the spread of HIV - target infected men.

"You could envision a vaccine that weakens the virus in chronically infected people and needed to be administered only once," he explained. "Their disease isn't weakened, but their virus is weakened. So when they have sexual contact, the chance of transmission is lowered."

The study was published in Science on July 11.