Tuesday, June 21, 2011

The Rapid Spread of the Vaccinia Virus

The Rapid Spread of the Vaccinia Virus

It is known that the Vaccinia virus produces one batch of viral particles every five to six hours. The Vaccinia virus however, can spread over vast areas of uninfected cells at a rate of 1.2 cells per hour (Smith 2011). This infection rate is far faster than seems possible; but new research is now providing an explanation for this microscopic mystery.

Vaccinia virus

Image: Vaccinia virus infecting host cell.

“This 'viral bouncing' accounts for experiments in which Vaccinia spreads much more quickly across a dish of cells than viral reproduction rates should allow,” says Geoffrey Smith of Imperial College London (Vastag 2010). So how is it that a virus is able to spread so rapidly? Geoffrey Smith and his team, at Imperial College London have discovered an answer to this question. Using live imaging of fluorescently tagged viruses, Smith noticed that the virus was actually tricking the cell into blasting its particles out large distances to new uninfected cells. At the same time the virus tags the infected cell as “infected” and thus signaling to other virus particles to move to another location. This sort of smart-bomb system is what has allowed the Vaccinia virus to spread great distances quickly (Vastag 2010).

Viral Launch Pads

Smith and his team utilized a specific strand of the Vaccinia virus. One that expresses the green florescent protein that shows up later in infection. Smith then had an easy identification signal that told him when a cell was infected (Smith 2011) (the cell would turn green). The Vaccinia virus would then enter a cell and infect its nucleus; exchanging its genetic information with the host cell’s. The virus then immediately turns on transcription and translation to produce two viral proteins known as A33 and A36 (Smith 2011). Other studies have shown that these proteins are escorted to the cell membrane by microtubules and microfilaments. When the proteins reach the membrane they diffuse through it and then rest on the outside of the cell in viral protein complexes (Vastag 2010). When a new viral particle comes in contact with this complex it initiates the creation of an actin arm that pushes the particles up, up, and away to infect another healthy host cell. With this new information Smith and his team went about crippling the A33 and A36 protein genes in the Vaccinia virus which resulted in the dramatic slowing of infection rates (Smith 2011). These two proteins however, were found to be fairly insufficient; as it takes the presence of both proteins simultaneously to initiate an actin projection from the cell membrane. If only one protein was present the viral particles would not bond to the protein complex and thus no propulsion would be executed (Smith 2011).

This spreading process is vital for a virus in its ability to survive. Though this process is not good for humans who contract these viruses, as Smith says “it is Darwinian,” and all things have equal right to survival (Smith 2011). This understanding of the Vaccinia virus is making scientist look closer at all viruses for this type of expansion mechanism. The Vaccinia virus its self is not harmful, but it closely mimics the small pox virus and has been used as a live vaccine for small pox in the past. These studies of the Vaccinia virus are very important milestones in the combat of all deadly diseases.



Smith, G.L. (2011). A mechanism for rapid virus spread. SGM Microbiology Today, 90-94. Retrieved from http://www.sgm.ac.uk/pubs/micro_today/pdf/051102.pdf

Vastag, B. (2010, January 21). Virus spreads by bouncing off infected cells. Nature News, 1, Retrieved from http://www.nature.com/news/2010/100121/full/news.2010.26.html

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