Wednesday, October 14, 1998 Published at 19:14 GMT 20:14 UK
Different HIV strains infect blood and semen
AZT: Drugs do not kill off all infection
HIV treatments that combat the virus in the blood may be useless at tackling infection in the semen, scientists have discovered.
Research indicates that men infected with HIV can have different strains of the virus in their blood and semen.
The discovery has major implications for the treatment of HIV and Aids.
It means that even when a blood test indicates that the infection has been significantly reduced in the blood, the virus may persist in the reproductive organs.
Alison Gray, health promotion officer for the Terrence Higgins Trust, said the research proved that there was no room for complacency in the fight against HIV.
She said: "This research shows that people have still got to practice safe sex.
"People may think that a low level of virus in the blood may mean they are less infectious, but there may well be a high level of the virus in the semen, and most people contract HIV through contact with semen, and not blood."
Swiss and American scientists conducted the research over a three-year period on 11 HIV-infected men.
No trace in semen
However, tests on the semen of the same two patients revealed no trace of the drug at all.
In another patient, the drug AZT was found in the sperm viruses, but only occurred later in the blood viruses.
The scientists claimed this was proof the reproductive organs and bloodstream acted as virtually independent "compartments" which had to be dealt with separately, and that the viruses in the bloodstream and the semen were not attacked by drugs in the same way.
The discovery was announced on Wednesday in the Aids Journal by two teams led by Dr Pietro Vernazza, from St Gall Cantonal Hospital, Switzerland, and Dr Joseph Eron, from University of North Carolina, USA.
They wrote in the journal: "Our observations may have substantial consequences for newly infected individuals and for public health."
They said it should be a public health priority to tackle HIV infection in the genital tract.