“Trojan virus” tricks healthy cells
A smallpox-related virus, which disguises itself as a piece of a broken cell to fool its way into cells, could lead to better drugs and vaccines, say scientists.
The discovery by researchers at the Federal Institute of Technology in Zurich could also contribute to combating the use of such viruses by bioterrorists.
The vaccinia virus tricks scavenging immune system cells into devouring it and can invade the body from there, according to Ari Helenius, who led the study published in the journal Science.
Helenius, a biochemist and winner in 2007 of the prestigious Marcel Benoist Prize – “the Swiss Nobel” – said vaccinia is used to make smallpox vaccines and as a research model for the more dangerous variola virus that causes smallpox.
“The virus is really fooling the cell,” he said on Thursday. “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, which affected 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, he explained. Most do so by binding to a cell and turning on a chemical signal that causes the cell to absorb the virus.
Target for drugs
Pox viruses, however, are ten times the size of most other viruses and far more complex. This means they have to find another way in to healthy cells, he said.
The virus achieves this by mimicking a piece of a broken cell to trick immune system cells called macrophages into picking them up and disposing of them as part of the normal process when cells die, the study found.
“What we are finding is the virus is disguised as a piece of garbage with the same ‘eat me’ signal,” Helenius said. “Instead of getting degraded, the virus escapes.”
The finding provides targets for drugs that would seek to block the healthy cells from bringing in the virus rather than targeting the virus itself, he added.
“Drugs are clearly what we are after. You can either target the virus or the Trojans involved.”
Biological weapons
Smallpox was eradicated in 1979 but many experts fear that samples of the virus, which when it was widespread killed 30 per cent of its victims, were developed into biological weapons in countries including Iraq and the former Soviet Union.
Because of this the US government began stockpiling smallpox vaccine after the September 11 attacks.
On Wednesday, British company Acambis said it had won a ten-year, $425 million (SFr442 million) contract with the US government to supply smallpox vaccines.
Smallpox is so dangerous because as an airborne disease it spreads easily and can kill within weeks, Helenius added.
“The main reason there is so much work on this virus is the threat of bioterrorism,” he said. “Smallpox is one of the worst plagues humans have ever had.”
swissinfo with agencies
A vaccinia virus infection is very mild and is typically asymptomatic in healthy individuals, but it may cause a mild rash and fever. Immune responses generated from a vaccinia virus infection protects the person against a lethal smallpox infection.
Due to the threat of smallpox-related bioterrorism, there is a possibility the vaccinia vaccine may have to be widely administered again in the future.
During the 20th century smallpox was responsible for 300-500 million deaths.
After successful vaccination campaigns throughout the 19th and 20th centuries using the vaccinia virus, the World Health Organization certified the eradication of smallpox in 1979. Smallpox is the only human infectious disease to have been completely eradicated from nature.
Ari Helenius has been a professor of biochemistry in Zurich since 1997.
He was born in 1944 in Oulu, Finland and studied biochemistry at Helsinki University.
He received his doctorate in 1973 and worked another six years as a staff scientist at the European Laboratory for Molecular Biology in Heidelberg, Germany.
He then moved to Yale in the United States and in 1983, he was given a full professorship in the department of cell biology.
From 1992 to 1997 he was chairman of this department.
His current research centres on membrane biology, virology and protein chemistry, using methods from biochemistry, cell and molecular biology.
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