PARIS (AFP) - The monkey version of HIV can take refuge from anti-Aids drugs within days of entering the body, a study said on Sunday, dampening hopes for a human cure.
If the same holds true for human beings, treatment may have to start "extremely early" after a person is infected with the virus that causes Aids, according to researchers publishing in the journal Nature.
The findings come just days after the disappointing announcement that a Mississippi baby thought to have been cleared of HIV through a potent dose of antivirals administered 30 hours after birth and continued for 18 months, has tested positive for the virus after two drug-free years.
"The unfortunate clinical findings of viral rebound in the Mississippi baby appear to be concordant with the monkey data," study co-author Dan Barouch of the Beth Israel Deaconess Medical Centre (BIDMC) in Massachusetts told AFP.
"These data certainly raise important challenges for HIV eradication efforts." A key challenge for curing HIV infection is the presence of viral reservoirs - infected immune cells in which virus DNA can lie dormant for years, undisturbed by antiretroviral treatment (ART) or the immune system.
In the vast majority of people, the virus starts proliferating as soon as treatment is stopped, which means the drugs have to be taken for life.
Little is known about when and where these reservoir cells are established during HIV infection.
Some had assumed the reservoirs are "seeded" by virus DNA during acute HIV infection - when the presence of virus in the blood had already risen to a high level.
But the new study found that in rhesus monkeys infected with simian HIV, or SIV, the reservoir was established "strikingly early" after infection.
"The reservoir was established in tissues during the first days of infection, before the virus was even detected in the blood," said Barouch.
The monkeys were started on antiretroviral treatment at three, seven, 10 and 14 days after SIV infection.
Once the drugs were stopped, the virus replicated in all groups, though slower in the monkeys treated earliest.
"The strikingly early seeding of the viral reservoir within the first few days of infection is sobering and presents new challenges to HIV-1 eradication efforts," the authors wrote.
"Taken together, our data suggest that extremely early initiation of ART, extended ART duration and probably additional interventions that activate the viral reservoir will be required." Scientists in Melbourne, Australia, are experimenting with an anti-cancer drug to flush the virus out of its hiding place, then to be killed.
The authors of the Nature paper stressed their findings have yet to be confirmed in humans, as there are important differences between SIV and HIV infection.
But if in humans the virus can also enter the reservoir even before it is detectable in the blood, it may be "very difficult" to start treatment early enough, as a blood test is required to diagnose HIV infection, said the team.
There is no cure for Aids, and antiviral drugs merely control the virus' replication, thus halting its spread.
Last week, US scientists said the Mississippi baby, who had had no detectable level of HIV for more than two years after stopping treatment, had tested positive for the virus.
Her case had raised hopes that doctors may have found a way to cure children born HIV-positive, simply by treating them early.
The new study was published as experts and policy makers from around the world gathered in Melbourne for the 20th International Aids Conference, which will discuss advances in prevention and treatment.