Salt In Semen, Breast Milk Aids HIV Transmission
NEW YORK, Feb 11
(Reuters Health) -- The higher salt content of seminal fluid and breast milk may overcome
the ability of saliva to fight HIV infection, according to researchers at the University
of Texas Medical Branch in Galveston. The finding helps to explain how semen and breast
milk transmit the virus via the mouth.
Salivary transmission of HIV is relatively rare, Dr. Samuel Baron and colleagues explain.
Saliva is thought to protect against HIV-transmitting white blood cells because of its
unique low salt concentration, which helps to kill these cells, the authors note in the
February issue of The Journal of Infectious Diseases. However, HIV is successfully
transmitted via seminal fluid, breast milk and colostrum, white cell-rich fluid secreted
in the first days of breastfeeding.
To further investigate how HIV-infected seminal fluid and milk overcome the protective
effects of saliva, Baron's team conducted a series of laboratory studies using mixes of
samples of saliva and milk, colostrum, and seminal fluid.
The researchers found that as the percentage of saliva was reduced, and the percentage of
seminal fluid, milk or colostrum was increased, the ability of saliva to inactivate
HIV-infected white blood cells decreased.
"When saliva was reduced to only one third of the mixture, with the remaining
two-thirds being the saltier substances, then saliva was no longer protective against
HIV," Baron commented in a University press release.
"Under normal circumstances, there is just about one-fifth of a teaspoon of saliva in
the mouth," he continued. "Deposited semen typically would equal more than four
times that volume and mother's milk much, much more. So it's easy to see that saliva can't
kill the infected cells because there's just too much of the saltier substances."
Baron also believes these findings have implications for the actual cause of HIV
infection. "There is very good evidence that infected white blood cells are the main
transmitting agent of HIV in the vagina and the rectum," he continued.
While many "physicians still believe that HIV is transmitted by free virus" from
HIV-infected individuals, "most cell-free virus is not infectious, probably because
HIV carriers make sufficient antibodies, which bind to the virus and hamper its ability to
infect other cells," Baron explained.
Conversely, "HIV-positive milk and semen are highly infectious, probably because
these fluids contain white blood cells that are infected by HIV and the antibodies can't
get inside these cells to attack the virus," he added.
Baron's group is currently trying to develop anti-HIV gel that can mimic the protective
effects of saliva in the vagina and rectum, environments that are both more salty than the
mouth.