A study of men who have sex with men, published last month in PLoS Pathogens, found that they are almost twice as likely as heterosexuals to contract multiple variants of HIV after a single exposure to the virus.

People who contract multiple variants of the HIV virus at infection can experience a more severe disease progression.

The factors affecting multivariant transmission are still uncertain, though the authors of the study propose that the biology of sexual organs may play a role in HIV transmission. Prior research has also indicated that inflammatory genital infections may be a factor.

Previous studies have shown that, in the majority of HIV cases, HIV infection is caused by the transmission of only one variant of the virus. Over time, the virus mutates and develops into multiple variants. However, people who transmit the virus still usually pass on only one variant, even if they are infected with multiple variants.

Approximately 20 percent of new HIV infections are the result of a multivariant transmission, when multiple variants of the virus are transmitted at once.

In their study, the researchers found that in men who have sex with men that number nearly doubled, to 36 percent.

The study consisted of 28 men who have sex with men whose main risk of transmission was through homosexual interactions. The participants were studied during acute infection, the period when the infection is still new but antibodies to HIV have been produced and are measurable.

The participants were studied using a new technique that enabled researchers to track viruses from donor to recipient. For the first time, researchers were able to determine the identity and number of the viruses that caused HIV infection upon transmission.

Researchers found that multiple viruses infected 10 of the 28 participants, or 36 percent. Some of the men had contracted up to 10 different variants of the virus.

The researchers suggested that the reason could be due to the “anatomical and [immune system] differences between the male and female genitourinary tracts and the lower intestine.”

They also concluded that the results of the study are consistent with the greater risk for male homosexuals of contracting HIV, which has been demonstrated previously.

Researchers pointed out that awareness of multivariant transmission could impact scientific understanding of how vaccinations are developed to effectively prevent the disease.

“The results of my studies provide a more clear picture of the transmission process at a basic and clinical level, and as such, they could be important for vaccine design and assessment and other prevention research,” said Dr. George Shaw, lead author of the paper in email correspondence with The AIDS Beacon.

The authors added that successfully identifying the factors that contribute to multivariant transmission could also help determine high-risk behaviors and prevent individuals from contracting more severe forms of the disease.

Multivariant transmission is different from superinfection, where a person is infected by HIV more than once through multiple, separate exposures to the virus. Superinfection is thought to be relatively rare.

For more information, please see the study on the PLoS Pathogens website.