RSS Feeds

Email a Friend Printer Friendly

Camelpox and smallpox more similar than originally thought

April 17, 2002

THE virus that causes camelpox is an even closer relative of the smallpox virus than scientists believed. This heightens fears about its potential risks, particularly because some experts fear that Iraq may be using it in its biological weapons programme.
        "It was surprising how close these two viruses were," says Geoffrey Smith of Imperial College in London, who has sequenced a strain of camelpox virus isolated from camels in Iran in 1970. "It could be that only a small set of changes would be necessary for camelpox virus to infect people."
        The viruses that cause smallpox and camelpox are both members of the orthopox family. The central region of the orthopox family`s genome usually varies little between species because it contains genes vital for replication. But the two sections either side of this do usually vary between species, since they govern variable features such as host range, infectiousness and tricks for evading the host`s immune system.
        It turns out that camelpox and smallpox are similar even in these outer regions. This suggests that camelpox might already have some of the genes needed to become a human pathogen, and could evolve to cause disease in people.
        For years there have been worries that a virus could evolve to fill the niche vacated by smallpox. "This process is inevitable," says Lev Sandakhchiev, head of Vector, the Russian laboratory that holds one of the two remaining official stocks of smallpox virus.
        But D. A. Henderson, who led the global campaign to eradicate smallpox, says there`s no evidence that camelpox virus could do this and he doubts that it would. The virus has so far shown little interest in humans, and camel handlers appear unharmed despite prolonged exposure. But there`s a lot of camelpox about. It is endemic among the world`s 20 million camels and there is no vaccine.
        But it`s possible that camel handlers show no symptoms of infection only because they are immunised by exposure at an early age. Adults who are new to camels, and lack immunity to any orthopoxes now that smallpox vaccination has stopped, might provide the virus with novel opportunities.
        In 1995, the Iraqi government admitted to UN weapons inspectors that its weapons scientists were working with camelpox. They claimed they wanted to use it as a weapon to which Iraqis, who are used to camels, would be immune, while foreign troops would not.
        The inspectors were dubious, as camelpox does not cause human disease. They feared that instead, Iraq might be using it as a safe substitute while testing a smallpox weapon. This heightened fears that Iraq has smallpox stocks-a continuing concern that has prompted the US to stockpile smallpox vaccine. Last week, the British government ordered £32 million worth of vaccine.
        The new results suggest camelpox itself could pose a threat. No one knows whether the Iraqis are still working on it. But if a lab is producing large quantities of the virus, selective pressures could accidentally lead to a human pathogen. It might even be possible to engineer one, suggests Sandakhchiev.

Authors: Andy Coghlan and Debora Mackenzie
More at: Journal of General Virology (vol 83, p 855)

New Scientist