The worldwide eradication of smallpox may,
inadvertently, have helped spread HIV infection, scientists
believe.
Experts say the vaccine used to wipe out smallpox offered some
protection against the Aids virus and, now it is no longer used,
HIV has flourished.
The US investigators said trials indicated the smallpox jab
interferes with how well HIV multiplies.
But they say in the journal BMC Immunology it is too early to
recommend smallpox vaccine for fighting HIV.
<!-- E SF -->
Kill no cure
Lead researcher Dr Raymond Weinstein, from Virginia's George
Mason University, said: "There have been several proposed
explanations for the rapid spread of HIV in Africa, including wars,
the reuse of unsterilised needles and the contamination of early
batches of polio vaccine.
"However, all of these have been either disproved or do not
sufficiently explain the behaviour of the HIV pandemic."
Dr Weinstein and his colleagues believe immunisation against
smallpox may go some way to explain the recent rises in HIV
prevalence.
Smallpox immunisation was gradually withdrawn from the 1950s to
the 1970s, following the worldwide eradication of the disease, and
HIV has been spreading exponentially since then, they say.
Now, only scientists and medical professionals working with
smallpox are vaccinated.
To test if the events may be linked, the researchers looked at
the white blood cells taken from people recently immunised against
smallpox and tested how they responded to HIV.
They found significantly lower replication rates of HIV in blood
cells from vaccinated individuals, compared with those from
unvaccinated controls.
The smallpox vaccine appeared to cut HIV replication
five-fold.
Immune boost
The researchers believe vaccination may offer some protection
against HIV by producing long-term alterations in the immune
system, possibly including the expression of a receptor called CCR5
on the surface of white blood cells, which is exploited by the
smallpox virus and HIV.
Jason Warriner, clinical director for the Terrence Higgins
Trust, said: "It's impossible to say whether the withdrawal of the
smallpox vaccine contributed to the initial explosion of HIV cases
worldwide, but it is a plausible explanation.
"This is an interesting piece of research, and not just as a
history lesson. Anything that gives us greater understanding of how
the virus replicates is another step on the road towards a vaccine
and, one day, a cure.
"Further studies into the role receptor cells play are needed,
and even then any discoveries are likely to be just one part of the
solution.
"Until we find a way to eradicate the virus from the body, the
focus should remain on stopping it being passed on in the first
place."
Source: http://news.bbc.co.uk/2/hi/health/8686750.stm