TWiV 329: Pox in the balance

On episode #329 of the science show This Week in Virology, the TWiV team reviews identification of immune biomarkers in CFS/ME patients, and how a cell nuclease controls the innate immune response to vaccinia virus infection.

You can find TWiV #329 at

TWiV 284: By the pricking of my thumbs, something wicked this way comes

On episode #284 of the science show This Week in Virology, the TWiV team discusses how skin scarification promotes a nonspecific immune response, and whether remaining stocks of smallpox virus should be destroyed.

You can find TWiV #284 at

TWiV 203: Mark Challberg, a cold room kind of guy

On episode #203 of the science show This Week in Virology, Vincent and Rich meet up with Mark Challberg to talk about his scientific career studying viral DNA replication, and his transition to an NIH Program Officer.

You can find TWiV #203 at

TWiV 198: Pox has got a squeeze-box, seals are gonna sneeze all night

On episode #198 of the science show This Week in Virology, Vincent, Alan, Rich, and Kathy review fatal avian influenza virus in harbor seals, and poxvirus deployment of genomic accordions to counter antiviral defenses.

There once was a virus named pox
Whose genome contained a squeeze-box
When placed under pressure
It expanded its measure
Overcoming the new cellular blocks

You can find TWiV #198 at

TWiV 194: Five postdocs in North America

On episode #194 of the science show This Week in Virology, Vincent returns to Madison, Wisconsin and meets with postdocs to discuss their science and their careers.

You can find TWiV #194 at

Now playing: Viral plaque formation

viral_plaquesOne of the most important procedures in virology is measuring the virus titer – the concentration of viruses in a sample. A widely used approach for determining the quantity of infectious virus is the plaque assay. In this technique, the spread of progeny viruses released by individually infected cells is restricted to neighboring cells by a semisolid medium. Consequently, each infectious particle produces a circular zone of infected cells called a plaque. By imagining live, virus-infected cells using a microscope, beautiful movies have been made which show how a plaque develops in real time.

To produce the movies, cells were infected with vaccinia virus, covered with a semi-solid medium, and placed in an incubator. The monolayers were examined periodically until a small plaque became visible. The infected cells were then placed on an inverted microscope fitted with a camera. Images of the plaque were taken every hour for 12-19 hours and assembled into a movie.

The first movie shows plaque formation on monkey cells infected with vaccinia virus. The virus infection begins at a small focus in the center, then spreads radially outwards. As the infection spreads, the cells undergo changes know as cytopathic effect. The large circle of dead cells would appear as a plaque if the monolayer were stained.

The second movie, made at higher magnification, shows spread at the edge of a viral plaque. The vaccinia virus used for this experiment carries the gene encoding enhanced green fluorescent protein (EGFP). Hence the infected cells fluoresce green as viral replication proceeds.

By showing very clearly how a viral plaque develops, these movies will be an invaluable teaching resource for years to come. I am grateful to the authors of this study for providing an up-close view of a technique that animal virologists have been using since 1952.

Doceul, V., Hollinshead, M., van der Linden, L., & Smith, G. (2010). Repulsion of Superinfecting Virions: A Mechanism for Rapid Virus Spread Science DOI: 10.1126/science.1183173