Alcohol abuse may increase susceptibility to HIV infection, researchers have found.
HIV infects the body's cells
The findings could be particularly significant as there is evidence that alcohol abuse is common among people who are HIV positive.
One study found that 41% of HIV-infected patients met the criteria for alcoholism.
The research, which was carried out on rhesus monkeys infected with a similar virus, shows that binge drinking poses the most significant problem.
Lead researcher Professor Gregory Bagby, of Louisiana State University, said there was evidence that people who abuse alcohol are more likely to engage in risky behaviours such as unprotected sex.
An increased risk of becoming infected with HIV is one of many reasons why young people should moderate their alcohol consumption
Thus there was reason to believe that these people are at greater risk of becoming infected with HIV.
However, his research suggests that once infected with the virus, they are also more vulnerable to its effects.
The researchers infected rhesus monkeys with simian immunodeficiency virus (SIV) after they had been given either regular doses of alcohol or a sugar solution.
Approximately one week after SIV infection, there was a 64-fold increase of the SIV virus in the blood of the alcohol-treated monkeys compared to those given the sugar solution.
Professor Bagby said: "This most likely means that either more cells are infected with virus at this early stage or that infected cells are producing more virus.
"If more cells are infected, it means that the alcohol increased infectivity of cells or increased the number of susceptible cells."
The reason why alcohol appears to increase HIV infectivity is unclear.
However, the researchers believe that it might activate immune cells called CD4+T cells, which are located in the wall of the gut which are known to be very vulnerable to becoming infected with HIV.
The researchers now plan to examine the long-term effects of alcohol abuse on the development of SIV-related disease.
It may help to explain why some people become infected with HIV when exposed to the virus, while others do not
Professor Bagby said: "Our study shows alcohol consumption may increase susceptibility to infection upon exposure to HIV.
"An increased risk of becoming infected with HIV is one of many reasons why young people should moderate their alcohol consumption."
Michael Carter, of the UK National Aids Manual, said the study was "very interesting" but still at a very early stage.
He told BBC News Online: "It may help to explain why some people become infected with HIV when exposed to the virus, while others do not."
Mark Graver, of the Terrence Higgins Trust, said: "Anything which has a significant effect on a person's immune system will increase the risk of that person contracting HIV if they are in a situation where HIV transmission is possible.
"Alcohol consumption on its own can also reduce a person's ability to make informed choices around safer sex and protecting themselves from HIV infection."
The research is published in the journal Alcoholism: Clinical & Experimental Research.