The virulence of a virus – its capacity to cause disease – is determined by both viral and host factors. Even among healthy individuals, infection with a particular virus may have different outcomes ranging from benign to lethal. The study of influenza viruses that cause mild or fatal outcomes reveals that defective viral genomes play a role in determining viral virulence.
Defective viral genomes and severe influenza
TWiV 480: The PFU in your achoo
Scott Hensley joins the TWiVites to review the current influenza season and presence of the virus in exhaled breath of symptomatic cases.
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Scott Hensley of the University of Pennsylvania helps us summarize the current influenza season so far. Bottom line: it’s a very serious season with a great deal of morbidity and mortality. As usually, serious disease and deaths occur in unvaccinated individuals. Although there is a mismatch between the influenza vaccine and this year’s H3N2 strain, which is causing most of the infections, vaccination still reduces disease severity cause by this strain, as well as by the circulating H1N1 and influenza B viruses. Next we discuss an interesting study of symptomatic college students with influenza. The goal was to determine which mode of influenza transmission is likely to be important: contact, or aerosols produced by speaking, coughing, or sneezing. The results show that simple breathing leads to virus in the breath – small aerosols that can travel distances to infect others. Coughing, but not sneezing, was a major observed sign of infection, but neither was needed for infectious aerosol generation.
A breath of fresh influenza virus
Influenza virus may be transmitted among humans in three ways: by direct contact with infected individuals; by contact with contaminated objects (called fomites, such as toys, doorknobs); and by inhalation of virus-laden aerosols. A recent study suggests that normal tidal breathing plays a substantial role in aerosol transmission.
TWiV 479: Trypsin the flight fantastic
The TWiVome explores induction of antiviral responses by repeating patterns of capsids, and a fungus in the mosquito gut that aids dengue virus replication.
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A human rhinovirus in chimpanzees
Rhinovirus receptors
An outbreak of respiratory disease in Ugandan chimpanzees provides insight into how virus infection can shape the genome and lead to differences in the cell receptor gene that regulate susceptibility to infection.
HPV vaccines do not encourage risky sexual behavior
The human papillomavirus (HPV) vaccines save lives by preventing lethal cervical and anogenital cancers. If Henrietta Lacks had received an HPV vaccine, she would not have succumbed to cervical cancer. Yet not enough young men and women receive the vaccine. An obstacle to more widespread adoption of the HPV vaccine is that some parents and clinicians feel that it encourages risky sexual behavior. The results of a recent study indicate that such fears are unfounded.
TWiV 477: Raiders of the lost Arc
The TWiVodrome explains how a gag-like protein from a retrotransposon forms virus-like particles that carry mRNA within vesicles across the synapse.
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Metabolic manipulations in virus-infected cells
The large quantities of viral macromolecules and virus particles that are produced in an infected cell impose heavy demands on the host. Synthesis of the building blocks of a virus particle – nucleotides, amino acids, and sometimes fatty acids – requires energy, typically in the form of ATP. Synthesis of viral proteins and genomes, and transport of viral components in the cell also require energy. Because of these needs, viral infections often lead to alterations in the energy-generating and precursor synthesizing pathways of a cell. Two recent examples illustrate how virus infection can alter host metabolism.
TWiV 476: In ACOD1 we trust
Nels joins the TWiV team to talk about his work on genomic accordions in vaccinia virus, hepatitis B virus in a 439 year old mummy, and viral induction of energy synthesis by a long noncoding RNA.
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Show notes at microbe.tv/twiv