MicrobiologyBytes

Herpes simplex virus (HSV) is an important pathogenic agent that causes recurrent oral and genital lesions, blindness and encephalitis. It is a member of the family Herpesviridae, which contains three subfamilies (alpha- beta- and gammaherpesvirinae) whose members infect humans to cause a variety of ailments, from benign rashes to nasopharyngeal carcinoma. Although this review focuses on HSV, the assembly steps that occur in the nucleus and the proteins involved are highly conserved among all family members, which suggests that antiviral agents that block these steps might be effective against many different herpesviruses and their associated diseases. Despite this potential, a broadly effective compound has yet to be realized, in part because many of the processes are only poorly understood in sufficient molecular detail. This review outlines these intranuclear assembly steps and illustrate potential and existing antiviral strategies that exploit them.

Herpes simplex virus capsid assembly and DNA packaging: a present and future antiviral drug target. (2011) Trends Microbiol. 19(12) :606-613

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Recent evidence shows that the quadrivalent HPV vaccine prevents several HPV-related diseases in men. However, despite the licensure of the vaccine in the USA for men 9 through 26 years of age, rates of male vaccination are very low. Research on acceptability, in general, indicates strong interest in vaccination among men, parents, and healthcare providers, though female vaccination is typically seen as a higher priority. Cost-effectiveness studies indicate that in the context of modest female vaccination rates and with the specification of a broad range of disease outcomes (e.g. genital warts, anogenital cancers, and oropharyngeal cancers), male vaccination can be quite cost-effective.

This review describes the indications for vaccinating men with the quadrivalent human papillomavirus (HPV) vaccine, reports on the U.S. rates of male vaccination, and reviews the recent research on acceptability of vaccinating men and research on the cost-effectiveness of adding men to existing female HPV immunization programs.

Summary: Men are at high risk for HPV infection and can benefit from vaccination, but vaccination rates among men remain extremely low. More research needs to be done on the predictors of uptake of HPV vaccine among men and on the development of interventions to increase male vaccination.

Human papillomavirus vaccine and men: what are the obstacles and challenges? (2012) Curr Opin Infect Dis. 25(1): 86-91

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By convention, the human adenovirus replication cycle is divided into two phases, an early and a late phase, which are separated by the onset of viral DNA replication. Based on temporal changes of the gene expression pattern as revealed by DNA microarray analysis, adenovirus type 2 (Ad2) infection in human primary lung fibroblasts can be divided into four periods. The first period is from 0 to 12 h after infection before or shortly after adenoviral gene expression has commenced. During this time, changes in cellular gene expression are likely to be triggered by the virus entry process, such as attachment of virus to cell surface receptors, and its intracellular transport along microtubules.

The second period covers the time from 12 to 24 h after infection and follows activation of the immediate early E1A gene. During this period, there is an increase in the number of differentially expressed cellular genes. About 50% of these genes are involved in cell cycle regulation, cell proliferation and antiviral response. The third period extends from 24 to 42 h after infection. By this time, the virus has gained control of the cellular metabolic machinery, resulting in an efficient replication of the viral genome. Additional changes in cellular gene expression are modest during this phase. During the fourth and last period, when the cytopathic effect becomes apparent, the number of down-regulated genes increases dramatically including many genes involved in intra- and extracellular structure.

The most intensive battle between the adenovirus and its host takes place during the second period after adenovirus genes expression has started. The major functions of the early gene products are to force the host cell to enter the S phase in order to provide optimal conditions for viral DNA replication and to suppress the host antiviral response. Adenoviruses encode several regulatory proteins within the early regions E1A, E1B, E3, and E4. The immediate-early E1A gene encodes two regulators of viral and cellular gene expression, the E1A-243R and E1A-289R proteins. The E1A proteins act as promiscuous transcriptional activators or repressors of cellular genes. E1A proteins are essential for promoting the host cell to enter the S phase. This is achieved by the binding of the E1A proteins to members of the retinoblastoma tumor suppressor (pRB) family, thereby releasing the E2F transcription factors, which are activators of genes required in the S-phase.

The transcriptome of the adenovirus infected cell. Virology. 9 Jan 2012
Alternations of cellular gene expression following an adenovirus type 2 infection of human primary cells were studied by using superior sensitive cDNA sequencing. In total, 3791 cellular genes were identified as differentially expressed more than 2-fold. Genes involved in DNA replication, RNA transcription and cell cycle regulation were very abundant among the up-regulated genes. On the other hand, genes involved in various signaling pathways including TGF-β, Rho, G-protein, Map kinase, STAT and NF-κB stood out among the down-regulated genes. Binding sites for E2F, ATF/CREB and AP2 were prevalent in the up-regulated genes, whereas binding sites for SRF and NF-κB were dominant among the down-regulated genes. It is evident that the adenovirus has gained a control of the host cell cycle, growth, immune response and apoptosis at 24h after infection. However, efforts from host cell to block the cell cycle progression and activate an antiviral response were also observed.

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When a virus infects a cell, it hijacks resources of the cell to manufacture and release a new generation of progeny virus particles. Yet despite its central importance, methods to precisely quantify virus production at the cellular level are lacking. Most approaches measure the production of virus by sampling from a population of infected cells, providing average values that mask the potentially wide-ranging and significant behaviors of individual cells.

Within a laboratory culture of virus-infected cells, or within a tissue of an infected host, individual cells can diverge in behavior from the average or majority of infected cells. However, these rare cells may nevertheless contribute importantly to the long-term behavior of the infection, well beyond their initial encounter with the virus. Because these rare cell behaviors are generally obscured during average-cell measures of infection, they highlight the need for single-cell measures of behavior that can be readily performed on many individual cells to reveal the extent of cell heterogeneity. This paper demonstrates a method to measure the kinetics of virus production from individual cells, without confounding effects from secondary infections. The method combines a series of simple steps that can be performed in any cell biology or virology facility, without reliance on specialized equipment.

Kinetics of virus production from single cells. Virology. 03 Jan 2012
The production of virus by infected cells is an essential process for the spread and persistence of viral diseases, the effectiveness of live-viral vaccines, and the manufacture of viruses for diverse applications. Yet despite its importance, methods to precisely measure virus production from cells are lacking. Most methods test infected-cell populations, masking how individual cells behave. Here we measured the kinetics of virus production from single cells. We combined simple steps of liquid-phase infection, serial dilution, centrifugation, and harvesting, without specialized equipment, to track the production of virus particles from BHK cells infected with vesicular stomatitis virus. Remarkably, cell-to-cell differences in latent times to virus release were within a factor of two, while production rates and virus yield spanned over 300-fold, highlighting an extreme diversity in virus production for cells from the same population. These findings have fundamental and technological implications for health and disease.

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First it was foot and mouth virus.
Then it was bluetongue virus.
Now it is Schmallenberg virus.
So here’s 10 things you didn’t know about Schmallenberg virus:

1. Schmallenberg virus was first isolated in Schmallenberg, Germany, in November 2011.
2. Schmallenberg virus is a Bunyavirus, one of a large group of of negative-stranded RNA viruses.
3. Why should I care? In cows, Schmallenberg virus causes fever and a drastic reduction in milk production. In sheep it causes congenital malformations and stillborn lambs (also stillborn calves in cows).
4. Schmallenberg virus was first identifed in the UK on 23rd January 2012.
5. Like Bluetongue, Schmallenberg virus is transmitted by midges (Culicoides spp.), which means we will be unlikely to be able to eradicate it – vaccination of anaimals is the only likely effective response.
6. Where did Schmallenberg virus come from? The virus genome is most closely related to sequences of a different Orthobunyavirus called Shamonda virus which belongs to the so-called Simbu serogroup known to infect ruminants and be transmitted by midges. In other words, it has form. But whether it is newly evolved (unlikely) or just newly discovered we don’t yet know.
7. How did Schmallenberg virus reach the UK? We don’t know. It could have been due to animal movements, but since it was first identifed in eastern England, it’s possible that it arrived in midges travelling under their own steam.
8. Is Schmallenberg virus going to spread to other parts of the UK and other countries? Yes, you can bet on that (just like bluetongue did).
9. Can I catch Schmallenberg virus? Honest answer: We don’t know. Possibly, but there have been no reports of human illness from areas where the virus is known to exist, so I wouldn’t worry too much.
10. Where can I find the latest news about Schmallenberg virus? Right here.
11. OK, one last time, why should I care? Because Schmallenberg virus is going to cost European and probably worldwide ecomonies millions of pounds. And that will affect you.

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Traditional approaches to phage therapy rely on the ability of viruses to kill their bacterial prey. However, the narrow host range or most bacteriophages and the ability of bacteria to become resistant to infection mean that in practice, using phage to simply replace antibiotics is not feasible. We need smarter approaches, which is where a recent paper comes in. Using phages to engineer sensitivity to antibiotics is a promising approach, but whether this proof-of-principle experiment ever makes it to the clinic is another matter.

Reversing bacterial resistance to antibiotics by phage-mediated delivery of dominant sensitive genes. (2011)Appl. Environ. Microbiol. 23 Nov 2011 doi: 10.1128/AEM.05741-11
Pathogen resistance to antibiotics is a rapidly growing problem, leading to an urgent need for novel antimicrobial agents. Unfortunately, development of new antibiotics faces numerous obstacles, and a method that will resensitize pathogens to approved antibiotics therefore holds key advantages. We present a proof-of-principle for a system that restores antibiotic efficiency by reversing pathogen resistance. This system uses temperate phages to introduce, by lysogenization, genes rpsL and gyrA conferring sensitivity in a dominant fashion to two antibiotics, streptomycin and nalidixic acid, respectively. Unique selective pressure is generated to enrich for bacteria that harbor the phages encoding the sensitizing constructs. This selection pressure is based on a toxic compound, tellurite, and therefore does not forfeit any antibiotic for the sensitization procedure. We further demonstrate a possible way of reducing undesirable recombination events by synthesizing dominant sensitive genes with major barriers to homologous recombination. Such synthesis does not significantly reduce the gene’s sensitization ability. Unlike conventional bacteriophage therapy, the system does not rely on the phage’s ability to kill pathogens in the infected host, but instead, to deliver genetic constructs into the bacteria, and thus render them sensitive to antibiotics prior to host infection. We believe that transfer of the sensitizing cassette by the constructed phages will significantly enrich for antibiotic-treatable pathogens on hospital surfaces. Broad usage of the proposed system, in contrast to antibiotics and phage therapy, will potentially change the nature of nosocomial infections toward being more susceptible to antibiotics rather than more resistant.

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It was my priveledge to work with Brian Mahy many years ago. Brian has just retired as long-serving Editor of Virus Research, and his swansong is an excellent special issue on negative strand RNA viruses – an important read for all virologists and an even more impirtant one for all aspiring virologists.

Virus Research: Negative Strand RNA Viruses Special Issue

• Insights on influenza pathogenesis from the grave
• Taming influenza viruses
• Induction and evasion of type I interferon responses by influenza viruses
• Immune responses to influenza virus infection
• Novel vaccines against influenza viruses
• Prospects for controlling future pandemics of influenza
• New concepts in measles virus replication: Getting in and out in vivo and modulating the host cell environment
• Recombinant vaccines against the mononegaviruses—What we have learned from animal disease controls
• Biological feasibility of measles eradication
• Progress in understanding and controlling respiratory syncytial virus: Still crazy after all these years
• An unconventional pathway of mRNA cap formation by vesiculoviruses
• Rhabdovirus accessory genes
• Structural insights into the rhabdovirus transcription/replication complex
• Hantavirus pulmonary syndrome
• Progress in recombinant DNA-derived vaccines for Lassa virus and filoviruses
• Borna disease virus – Fact and fantasy
• A review of Nipah and Hendra viruses with an historical aside
• Negative-strand RNA viruses: The plant-infecting counterparts
• Quasispecies as a matter of fact: Viruses and beyond

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I recently wrote about the top 10 plant viruses in molecular plant pathology. Well Ed didn’t like that list, so he’s published his own:

1. Tobacco mosaic virus (TMV)
2. Tomato spotted wilt virus (TSWV)
3. Tomato yellow leaf curl virus (TYLCV)
4. Cucumber mosaic virus (CMV)
5. Potato virus Y (PVY)
6. Cauliflower mosaic virus (CaMV)
7. African cassava mosaic virus (ACMV)
8. Plum pox virus (PPV)
9. Brome mosaic virus (BMV)
10. Potato virus X (PVX)

“I see only ONE virus in the major list – African cassava mosaic begomovirus (ACMV) – that infects and causes severe losses in one of the four major food crops grown on this planet: all the rest, excepting viruses infecting the also-ran potato, are pathogens of fruits, vegetables or horticulturally-important plants. Or hardly pathogenic at all, as in the case of BMV – and before anyone argues, I probably have the best collection of African (and other) isolates of the virus in the world, and a lot of experience of it in the field.”

I have a feeling this could go on for some time :-)

Many scientists, if not all, feel that their particular plant virus should appear in any list of the most important plant viruses. However, to our knowledge, no such list exists. The aim of this review was to survey all plant virologists with an association with Molecular Plant Pathology and ask them to nominate which plant viruses they would place in a ‘Top 10′ based on scientific/economic importance. The survey generated more than 250 votes from the international community, and allowed the generation of a Top 10 plant virus list including, in rank order:

• Tobacco mosaic virus
• Tomato spotted wilt virus
• Tomato yellow leaf curl virus
• Cucumber mosaic virus
• Potato virus Y
• Cauliflower mosaic virus
• African cassava mosaic virus
• Plum pox virus
• Brome mosaic virus
• Potato virus X

This review article presents a short review on each virus of the Top 10 list and its importance, with the intent of initiating discussion and debate amongst the plant virology community, as well as laying down a benchmark, as it will be interesting to see in future years how perceptions change and which viruses enter and leave the Top 10.

Top 10 plant viruses in molecular plant pathology. (2011) Mol Plant Pathol. 12(9): 938-954. doi: 10.1111/j.1364-3703.2011.00752.x

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