virology blog
About viruses and viral disease
Virus particles are metastable: they must be highly stable, to protect the nucleic acid while traveling from host to host or cell to cell, and then come apart to liberate the genome into the cell. New insight into this uncoating process comes from beautiful images of feline calicivirus showing formation of a portal on the capsid upon receptor engagement.
The TWiV crew reveal a unique portal on the calcivirus capsid formed upon receptor engagement, and the regulation of interferon responses in virus-infected cells by methylation of mRNA.
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On episode #312 of the science show This Week in Virology, the TWiVbolans discuss the finding that human noroviruses, major causes of gastroenteritis, can for the first time be propagated in B cell cultures, with the help of enteric bacteria.
You can find TWiV #312 at www.microbe.tv/twiv.
Hosts: Vincent Racaniello, Rich Condit, Dickson Despommier, Alan Dove, and Stephanie KarstVincent, Rich, Alan, and Dickson review noroviruses with Stephanie Karst, PhD.
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Stephanie – Effectors of the type I interferon response (Nature)
Dickson – Receptor for Ebola virus (PNAS)
Rich – A History of Vaccines
Alan – The Worst Journey in the World by Apsley Cherry-Garrard
Vincent – ASM Live 2011 webcast
Sophie  – TED talk app for iPad and iPhone
Send your virology questions and comments (email or mp3 file) to twiv@microbe.tv, or call them in to 908-312-0760. You can also post articles that you would like us to discuss at microbeworld.org and tag them with twiv.
Hosts: Vincent Racaniello, Rosa Maria del Angel, and Ana Lorena GutiérrezOn episode #109 of the podcast This Week in Virology, Vincent visits Mexico City and speaks with Rosa Maria del Angel and Ana Lorena Gutiérrez about virology in Mexico, and their work on dengue and caliciviruses.
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Weekly Science Picks
Lorena – Caliciviruses by Hansman, Jiang, and Green
Vincent – Insights into dengue virus genome replication by Alcaraz-Estrada, Yocupicio, and del Angel
Send your virology questions and comments (email or mp3 file) to twiv@microbe.tv or leave voicemail at Skype: twivpodcast. You can also post articles that you would like us to discuss at microbeworld.org and tag them with twiv.
Viruses can be transmitted to completely new host species that they have not previously infected. Usually host defenses stop the infection before any replication and adaptation can take place. On rare occasions, a novel population of viruses arises in the new host. These interspecies infections can sometimes be deduced by sequence analyses, providing a glimpse of the amazing and unpredictable paths of virus evolution. One example is a plant virus that switched hosts and infected vertebrates.
Circoviruses infect vertebrates and have small, circular, single-stranded DNA genomes. Nanoviruses have the same genome structure, but infect plants. The genes encoding one of the viral proteins – called the Rep protein – appear to be hybrids, and share significant sequence similarity. They also exhibit homology with a protein encoded by caliciviruses, which are RNA viruses that infect many different vertebrates.
Analysis of the viral DNA sequences suggests that two remarkable events occurred during the evolution of circoviruses and nanoviruses. Not long ago, a nanovirus was transmitted from a plant to a vertebrate. This event might have occurred when a vertebrate fed on an infected plant. The virus adapted to vertebrates, and the circovirus family was established. After the host switch from plants to vertebrates, recombination took place between the circovirus and a vertebrate calicivirus. A reverse transcriptase probably converted the circovirus RNA genome to DNA to allow recombination to occur.
Similar interspecies transmission events have lead to outbreaks of human disease. One notable example is the transfer of simian immunodeficiency virus-1 from chimpanzees to humans. This host switch event, which is believe to have occurred in the early part of the 20th century, lead to the current AIDS pandemic.
Gibbs, M. (1999). Evidence that a plant virus switched hosts to infect a vertebrate and then recombined with a vertebrate-infecting virus Proceedings of the National Academy of Sciences, 96 (14), 8022-8027 DOI: 10.1073/pnas.96.14.8022