Study shows how smallpox virus tricks healthy cells

By Michael Kahn

LONDON (Reuters) - A virus closely related to smallpox disguises itself as a piece of a broken cell to trick its way into cells, Swiss researchers said on Thursday in a discovery that could lead to better drugs and vaccines.

The vaccinia virus tricks scavenging immune system cells into devouring it, and can invade the body from there, said Ari Helenius, who led the study published in the journal Science.

Vaccinia is used to make smallpox vaccines and as a research model for the more dangerous variola virus that causes smallpox, said Helenius, a biochemist at the Swiss Federal Institute of Technology.

"The virus is really fooling the cell," he said in a telephone interview. "It is deposited outside the city wall and for the cell to get invaded by the virus what must happen is for the Trojans to bring the virus in."

There are other pox viruses such as monkeypox spread by animals but researchers are focused on smallpox because of fears it could be used as a biological weapon.

A 2003 outbreak of monkeypox in the United States that sickened a family exposed to an infected prairie dog highlights the threat from other strains as well, Helenius said.

Viruses have devised many ways of entering cells, Helenius said. Most do so by binding to a cell and turning on a chemical signal that causes the cell to absorb the virus.

Pox viruses, however, are 10 times the size of most other viruses and far more complex. This means they have to find another way in to healthy cells, Helenius said.