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Eradication of smallpox may have set the stage for HIV pandemic, study says

May 18, 2010 | 11:51 am

The worldwide eradication of smallpox in the mid-20th century was a remarkable public health achievement, but it may have set the stage for the HIV pandemic of the latter half of the century, researchers reported Tuesday.

Laboratory tests suggest that immunity to smallpox triggered by the vaccinia (smallpox) vaccine can inhibit the replication of the AIDS virus. Such vaccination could have kept HIV transmission partially under control in the early days of the outbreak, but withdrawal of the smallpox vaccine in the 1950s would have freed it to spread unfettered, the researchers said.

The most common form of HIV is thought to have evolved from a simian immunodeficiency virus found in chimpanzees of southern and western Africa sometime around 1931. It spread slowly until the mid- to late-1950s, when it began to spread exponentially. Wars, misuse of medical equipment and contamination of a polio vaccine have been suggested as possible causes of the spread, but such theories have either been disproved or do not sufficiently explain the behavior of the HIV pandemic, said Dr. Raymond S. Weinstein of the biodefense program at George Mason University in Manassas, Va.

Weinstein and his colleagues noted that the progression of an HIV infection can be mitigated by a co-infection with certain other viruses, such as human herpesvirus 6 or 7 or the paramyxovirus that causes measles. Such viruses interfere with a cellular receptor of white cells that is also used by HIV. The vaccinia virus also blocks this receptor.

To test their idea, Weinstein and his colleagues recruited 20 Navy personnel. Half had received normal vaccinations and half had received both those vaccinations and, within the previous three to six months, vaccination against smallpox. The researchers extracted white blood cells from all the subjects and exposed them to HIV in a culture dish. They reported in the journal BMC Immunology that HIV replication was slowed by about 80% in the cells from those who had received smallpox vaccination.

"While these results are very interesting and hopefully may lead to a new weapon against the HIV pandemic, they are very preliminary and it is far too soon to recommend the general use of vaccinia immunization for fighting HIV," Weinstein said in a statement. Given the great difficulties researchers have encountered in trying to develop an HIV vaccine, the ironic fact is that we may once have had a vaccine that is more effective against the virus than anything that has since been developed, and we threw it away.

-- Thomas H. Maugh II