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TWiV 554: Full fathom five thy viromes lie

30 June 2019 by Vincent Racaniello

A trio of TWiVers reports on influenza in Australia, how a host protein impacts bird to human movement of influenza virus, and marine DNA viral diversity in the oceans from pole to pole.

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Show notes at microbe.tv/twiv

Filed Under: This Week in Virology Tagged With: ANP32, H1N1, H3N2, influenza drift, influenza host range, influenza in Australia, influenza RNA polymerase, influenza vaccine, marine viruses, metagenomics, viral, viral communities, virology, virus, viruses

Defective viral genomes and severe influenza

15 February 2018 by Vincent Racaniello

Defective influenza virus RNAsThe 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.

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Filed Under: Basic virology, Information Tagged With: defective viral genome, DI particles, H1N1, influenza, interferon, pandemic, viral, virology, virulence, virus, viruses

TWiV 446: Old sins die hard

18 June 2017 by Vincent Racaniello

The TWiV hosts review an analysis of gender parity trends at virology conferences, and the origin and unusual pathogenesis of the 1918 pandemic H1N1 influenza virus.

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Filed Under: This Week in Virology Tagged With: 1918 pandemic, gender parity, H1N1, influenza virus, Spanish flu, viral, virology, virology conferences, virus, viruses

Influenza virus in breast milk

12 November 2015 by Vincent Racaniello

Ferret mother-infantDuring breastfeeding, mothers provide the infant with nutrients, beneficial bacteria, and immune protection. Fluids from the infant may also enter the mammary gland through retrograde flux of the nipple. Studies in a ferret model reveal that influenza virus replicates in the mammary gland, is shed in breast milk and transmitted to the infant. Virus may also travel in the opposite direction, from infant to mother.

The role of the mammary gland in influenza virus transmission was studied using a ferret model comprising lactating mothers and nursing infants. Intranasal inoculation of nursing mother ferrets with the 2009 H1N1 influenza virus lead to viral replication and development of influenza in both mother and infant. When the study design was reversed, and 4 week old nursing ferrets were inoculated intranasally with the same virus, viral replication and disease ensued first in the infants, and then in the mothers. Infectious virus was recovered both in the mammary glands and in the nipples at day 4 post infant inoculation, and in mother’s milk from 3-5 days post infant inoculation. Histopathological examination of sections of mammary glands from infected mothers revealed destruction of the mammary architecture.

These results show that nursing infants may pass influenza virus to mothers. It seems clear that influenza virus replicates in the mammary gland and that infectious virus is present in milk. How does this virus infect the mother? One possibility is that infection is transmitted by respiratory contact with virus-containing milk, or by inhalation of aerosols produced by nursing. How influenza virus in the mammary gland would reach the mother’s lung via the blood to cause respiratory disease is more difficult to envision and seems unlikely.

When influenza virus was inoculated into the mammary gland of lactating mothers via the lactiferous ducts, both mother and breast feeding infant developed serious influenza. Infectious virus was detected first in the nasal wash of infants, then later in the nasal wash of mothers. Breast milk contained infectious virus starting on day 2 after inoculation. Histopathological examination of sections from infected mammary glands revealed destruction of glandular architecture and cessation of milk production. This observation is consistent with the results of gene expression analysis of RNA from virus infected mammary glands, which revealed reduction in transcripts of genes associated with milk production.

To determine if human breast cells can be infected with influenza virus, three different human epithelial breast cell lines were infected with the 2009 H1N1 virus strain. Virus-induced cell killing was observed and infectious virus was produced.

Even if we assume that influenza virus can replicate in the human breast, the implications for influenza transmission and disease severity are not clear. Transmission of HIV-1 from mother to infant by breast milk has been well documented. In contrast to influenza virus, HIV-1 is present in the blood from where it spreads to the breast. Most human influenza virus strains do not enter the blood so it seems unlikely that virus would spread to the breast of a mother infected via the respiratory route. However, viral RNA has been detected in the blood of humans infected with the 2009 H1N1 strain, the virus used in these ferret studies. Therefore we cannot rule out the possibility that some strains of influenza virus spread from lung via the blood to the breast, allowing infection of a nursing infant. Some answers might be provided by determining if influenza virus can be detected in the breast milk of humans with influenza.

What would be the implication of a nursing infant infecting the mother’s breast with influenza virus? As I mentioned above, it seems unlikely that this virus would enter the blood, and even if it could, how would the virus infect the apical side of the respiratory epithelium? What does seem clear is that viral replication in the breast could lead to a decrease in milk production which could be detrimental to the infant. If the mother had multiple births, then influenza virus might be transmitted to siblings nursing on the infected mother.

Are you wondering how an infant drinking influenza virus-laded breast milk acquires a respiratory infection? Recently it has been shown that influenza virus replicates in the soft palate of ferrets. The soft palate has mucosal surfaces that face both the oral cavity and the nasopharynx. Ingested virus could first replicate in the soft palate, then spread to the nasopharynx and the lung. A simpler explanation is that nursing produces virus-containing aerosols which are inhaled by the infant.

Filed Under: Basic virology, Information Tagged With: aerosol, breast, breastfeeding, H1N1, infant, influenza, influenza virus, mammary gland, milk, mother, pandemic, transmission, viral, virology, virus

TWiV 351: The dengue code

23 August 2015 by Vincent Racaniello

On episode #351 of the science show This Week in Virology, the Masters of the ScienTWIVic Universe discuss a novel poxvirus isolate from an immunosuppressed patient, H1N1 and the gain-of-function debate, and attenuation of dengue virus by recoding the genome.

You can find TWiV #351 at www.microbe.tv/twiv.

Filed Under: This Week in Virology Tagged With: attenuation, codon bias, codon pair bias, dengue virus, dinucleotide bias, gain of function, H1N1, immunosuppressed, influenza virus, kidney transplant, poxvirus, reversion, translation, vaccine, viral, virology, virus

TWiV 343: The silence of the turnips

28 June 2015 by Vincent Racaniello

On episode #343 of the science show This Week in Virology, the TWiVerinoes discuss the potential for prion spread by plants, global circulation patterns of influenza virus, and the roles of Argonautes and a viral protein in RNA silencing in plants.

You can find TWiV #343 at www.microbe.tv/twiv.

Filed Under: This Week in Virology Tagged With: Ago, Arabidopsis thaliana, argonaute, chronic wasting disease, dicer, epidemiology, global circulation, H1N1, H3N2, HC-Pro, influenza virus, plant, potyvirus, prion, rna silencing, rnai, transmissible spongiform encephalopathy, turnip mosaic virus, viral, virology, virus

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