TWiV 237: Paleovirology with Michael Emerman

Episode #237 of the science show This Week in Virology was recorded at the Fred Hutchinson Cancer Research Center in Seattle, WA, where Vincent and Rich met up with Michael to talk about his work on the molecular and evolutionary basis of HIV replication and pathogenesis.

You can find TWiV #237 at

Inefficient influenza H7N9 virus aerosol transmission among ferrets

ferretThere have been 131 confirmed human infections with avian influenza H7N9 virus in China, but so far there is little evidence for human to human transmission. Three out of four patients report exposure to animals, ‘mostly chickens‘, suggesting that most of the infections are zoonoses. Whether or not the virus will evolve to transmit among humans is anyone’s guess. Meanwhile it has been found that one of the H7N9 virus isolates from Shanghai can transmit by aerosol among ferrets, albeit inefficiently.

Ferrets were inoculated intranasally with influenza A/Shanghai/02/2013 virus or A/California/07/2009, the 2009 pandemic H1N1 virus. One to two days later the ferrets developed fever, sneezing, coughing, and nasal discharge; both viruses induced similar clinical signs. Virus was shed in nasal secretions for 7 days. Six infected ferrets were then divided among three separate cages, and each group was housed with a naive ferret, and a second uninfected animal was placed in an adjacent cage. Airflow was controlled so that air flowed from the cage of infected animals towards the cage of naive animals. Transmission of infection was measured by observing clinical signs, and measuring virus shedding in nasal secretions and hemagglutination-inhibition antibodies in serum.

Of the three ferrets housed in the same cage with H7N9 virius-infected animals, all three had signs of infection (sneeze, cough, nasal discharge), shed virus in nasal secretions, and developed anti-HA antibodies. All three ferrets in neighboring cages developed signs of infection, but only one shed virus in nasal secretions, and two of three seroconverted. From these data the authors conclude that H7N9 virus is ‘efficiently transmitted between ferrets by direct contact, but less efficiently by airborne exposure’. In contrast, transmission of H1N1 virus to naive ferrets by contact or aerosol was efficient (3/3 animals in both cases).

The authors also found that pigs could be infected intranasally with A/Shanghai/02/2013 virus: the animals shed virus in nasal secretions and developed clinical symptoms. However the infected pigs transmitted infection inefficiently to other pigs by contact or aerosol, or to ferrets by aerosol.

The  authors’ equivocal conclusion that “Under appropriate conditions human to human transmission of the H7N9 virus may be possible” could have been reached even before these experiments were done. Their results provide no information on whether the virus can undergo human to human transmission because animal models are not definitive predictors of what might occur in humans. I disagree with the authors’ statement on page 5, “Efficient transmission of influenza viruses in ferrets is considered as a predictor of human to human transmissibility’. While many influenza virus strains that transmit among humans by aerosol also do so in ferrets, this does not mean that human transmission of a novel virus can be predicted by animal experiments.

Infection of ferrets with A/Shanghai/02/2013 or or A/California/07/2009 virus results in mild disease with no mortality. In contrast, 32 humans infected with H7N9 virus have died, and many humans have died after H1N1 infection. These findings further emphasize the differences in influenza virus pathogenesis in ferrets and humans.

TWiV 226: Taking the viral A train with Terry Dermody

On episode #226 of the science show This Week in Virology, Vincent and Dickson speak with Terry Dermody about his career in medicine and virology.

You can find TWiV #226 at

A virology course for all

Virology class 2013The spring semester has begun at Columbia University, which means that it is time to teach my virology course.

The fourth annual installment of my virology course, Biology W3310, has begun. This course, which I taught for the first time in 2009, is intended for advanced undergraduates and convenes at the Morningside Campus. Until I started this course, no instruction in virology had been offered at the Morningside Heights campus of Columbia University since the late 1980s. This is a serious omission for a first-class University. Sending graduates into the world without even a fundamental understanding of viruses and viral disease is inexcusable.

Course enrollment has steadily increased: 45 students in the 2009, 66 students in 2010, 87 students in 2012 and an amazing 195 students this year. I am gratified that so many students want to learn about the world of viruses. This year our class was moved into a wonderful lecture hall in the brand-new Northwest Corner building.

Readers of virology blog can watch every lecture in the course. You will find a videocast of each lecture at the course website, at my YouTube channel, and at iTunes University. The complete 2012 version of this course is available online, at iTunes University, and YouTube.

This year we will also be offering my virology course at Coursera. Details will be forthcoming.

To those who would like to know if the 2013 version of my course differs from the 2012 version, I reply: do viruses change? Some parts will be the same, others will be different. The goal of my virology course is to provide an understanding of how viruses are built, how they replicate and evolve, how they cause disease, and how to prevent infection. After taking the course, some of the students might want to become virologists. The course will also provide the knowledge required to make informed decisions about health issues such as immunization against viral infections. It should also be possible to spot badly constructed headlines about virology stories.

I am excited about teaching virology to 195 Columbia University students this year. But the internet makes it possible to spread the word even further. So far nearly 75,000 students registered for the iTunes University version of my 2012 virology course! As a professor used to teaching relatively small numbers of students in a classroom, this reach is truly amazing.

Virology lecture: Picornaviruses

I was scheduled to deliver a lecture on picornaviruses to a virology class at Yale University this week, but had to cancel at the last minute. I prepared this screencast to make up for my absence.

The Picornaviridae is a family of non-enveloped, positive-strand RNA viruses which contains some well known viruses including poliovirus, rhinovirus, hepatitis A virus, enterovirus 71, and foot-and-mouth disease virus. In this lecture I cover basic aspects of picornavirus replication and pathogenesis, including attachment and entry, translation and protein processing, RNA synthesis, assembly and release, disease and immunization.

How lethal is rabies virus?

Desmodus rotundusWhen I am asked to name the most lethal human virus, I never hesitate to name rabies virus. Infection with this virus is almost invariably fatal; just three unvaccinated individuals have been known to survive. New evidence from humans in the Peruvian Amazon suggests that the virus might be less lethal than previously believed.

Rabies virus is typically transmitted to humans by the bite of an infected mammal, often a carnivore or a bat. Recently there have been numerous outbreaks of rabies in Peru that have been linked to bites of vampire bats. A study of two communities at risk for vampire bat bites was undertaken to determine whether subclinical infection with rabies virus might occur. Over half of 92 individuals interviewed reported having been bitten by bats. Neutralizing antibodies against rabies virus were detected in 7 of 63 serum samples obtained from this population. Antibodies against the viral nucleoprotein were found in three individuals, two of whom were also positive for viral neutralizing antibodies. All 9 seropositive individuals indicated that they had previously had contact with a bat (a bite, scratch, or direct contact with unprotected skin). One of these individuals had previously received rabies vaccine.

The finding of neutralizing antibodies against rabies virus suggests that these individuals were likely infected, but did not develop fatal disease. It is also possible that they received a sufficiently large dose of virus to induce antibodies, but that viral replication did not occur. Another explanation for the findings is that these individuals were infected with an unknown virus that is highly related to rabies virus, but which is not pathogenic for humans.

There have been numerous seroprevalence studies of rabies infection in wildlife. For example, foxes and other canids have low (0-5%) seroprevalence rates, while 5-50% of bats can harbor rabies neutralizing antibodies, indicating that these animals are less susceptible to fatal rabies. In contrast, there have been few studies on rabies seroprevalence in humans. In one study of 30 raccoon hunters in Florida, low levels of rabies virus neutralizing antibodies were found in 2 samples. Low neutralizing antibody titers were also detected in 9 of 31 Canadian Inuit hunters; in a separate study, high rabies antibody titers were detected in the serum of 1 of 26 Alaskan fox trappers. All of these individuals had not been immunized with rabies virus vaccine.

Rabies virus causes 55,000 human deaths each year, so even if the results of the Peruvian study indicate subclinical infection, they would have little impact on the nearly 100% fatality rate associated with infection. More extensive studies are needed to determine if nonfatal human rabies infection is more common than believed. Understanding why some individuals do not die after infection might reveal immunological and genetic factors that protect against the disease.

Amy T. Gilbert, Brett W. Petersen, Sergio Recuenco, Michael Niezgoda, Jorge Gómez, V. Alberto Laguna-Torres and Charles Rupprecht. Evidence of Rabies Virus Exposure among Humans in the Peruvian Amazon. Am. J. Trop. Med. Hyg. 87:206 (2012).


How lethal is ebolavirus?

Should we fear avian H5N1 influenza?

Transgenic mice susceptible to poliovirus

pvr transgenic mouseYesterday I terminated the last remaining mice in my small colony, including the line of poliovirus receptor transgenic mice that we established here in 1990. Remarkably, I had never written about this animal model for poliomyelitis which has played an important role in the work done in my laboratory.

While I was still working on poliovirus as a postdoctoral fellow with David Baltimore, I became interested in how the virus causes disease. There were no convenient animal models to study poliovirus pathogenesis, so I began to think about the cellular receptor for the virus and how it could be used to make a mouse model for infection. When I moved to Columbia University Medical Center in 1982, I decided to identify the cellular gene for the poliovirus receptor. This work was carried out by the second graduate student in my lab, Cathy Mendelsohn. She identified a gene from human cells that encoded a protein which we believed to be the cellular receptor for poliovirus. When this human gene was expressed in mouse cells, it madepvr model them susceptible* to poliovirus infection (the mouse cells were already permissive for poliovirus replication). The gene encodes a transmembrane glycoprotein (illustrated) that we called the poliovirus receptor (PVR), later renamed CD155. Over the years we worked extensively on PVR, with the goals of understanding its interaction with poliovirus during entry into the cell. In one project we collaborated with Jim Hogle, David Belnap, and Alasdair Steven to solve the structure of poliovirus bound to a soluble form of PVR. The image of that complex decorates the banner at virology blog and

Shortly after identifying PVR as the cellular receptor for poliovirus, a new student, Ruibao Ren, joined my lab. For his project I suggested he create transgenic mice with the human gene for PVR. We already knew that synthesis of PVR in mouse cells allowed the complete poliovirus replication cycle. Together with Frank Costantini and JJ Lee, Ruibao produced PVR transgenic mice and showed that they were susceptible to poliovirus infection. The illustration at top left shows a PVR transgenic mouse with a paralyzed left hind limb after poliovirus inoculation.

Poliovirus transgenic mice were used for many years in my laboratory to study how the virus causes disease, and to identify the mutations that attenuate the neurovirulence of the Sabin vaccine strains. A good summary of this work can be found in my review, ‘One hundred years of poliovirus pathogenesis‘. But there is a dark side of this story that I wish to briefly recount. When we first developed PVR transgenic mice, my employer decided to patent the animals. Until the patent issued, we could not share the transgenic mice with other researchers. As a consequence, others developed their own lines of PVR transgenic mice. One of these lines has been qualified by the World Health Organization to determine the neurovirulence of the Sabin vaccine strains. However, Columbia University realized little income from the PVR transgenic mice – such animals cannot be patented in Europe. By patenting the mice, we simply delayed research progress. Because of this experience I am personally very wary about patenting biological discoveries.

There are several reasons why I decided to stop doing research with mice. The cost of housing and breeding mice is very high, nearly $1.00 US per cage per day, and I simply don’t have the funds to support such work. More importantly, no one in my laboratory has any interest in working with mice: the last student to do mouse work left years ago. Although there are many interesting experiments to be done using viruses and mice, that line of work ended for the Racaniello lab on 11 July 2011.

*A susceptible cell bears the receptor for the virus; a permissive cell allows viral replication. A susceptible and permissive cell allows the complete viral replication cycle.

 Ren, R., Costantini, F., Gorgacz, E., Lee, J., & Racaniello, V. (1990). Transgenic mice expressing a human poliovirus receptor: A new model for poliomyelitis Cell, 63 (2), 353-362 DOI: 10.1016/0092-8674(90)90168-E

XMRV infection of Rhesus macaques

rhesus macaqueThe first detailed study of infection of nonhuman primates with the retrovirus XMRV reveals that the virus establishes a persistent infection characterized by infection of multiple tissues. Viremia (virus in the blood) is low and transient, with proviral DNA detectable in blood lymphocytes. The results show that the Rhesus macaque can be used to study XMRV infection, transmission, vaccines, and antiviral drugs.

The subject of this study, the Rhesus macaque (Macaca mulatta), was selected because of its evolutionary proximity to humans and a comparable immune system. The monkeys used did not have antibodies to the capsid protein p30 of XMRV, indicating that they were not previously infected. Animals were inoculated intravenously with 3.6 million TCID50 of purified XMRV – a good amount of virus, to ensure infection. The virus used, VP62, was produced by transfecting cells with cloned viral DNA isolated from human prostate.

Virus in the plasma fraction of blood was assayed by quantitative RT-PCR. Of three animals infected, virus was detected in one animal at day 4 and not after day 14; and in a second animal from days 14-20. The third animal did not develop detectable viremia. Proviral DNA was found in peripheral blood mononuclear cells (PBMC) of all three monkeys for 3-4 weeks, indicating successful infection. At one month post-infection proviral DNA was no longer detected. Plasma virus was again detected in one of the positive animals on day 291, 16 days after being immunized with a mixture of XMRV proteins. This means that viral DNA had been present in this animal but was not detected. XMRV was detected in CD4+ and CD8+ T cells and NK cells, but not in B cells or monocytes.

Rhesus macaques infected with XMRV did not display obvious clinical symptoms. Analysis of peripheral blood revealed increases in the number of circulating B and NK cells. Anti-viral antibody titers were detected after infection and re-infection of animals but soon decreased.

Other infected animals were sacrificed during the acute phase of infection to identify pathological changes and sites of virus replication. No pathogenic consequences were observed except for the formation of germinal centers in spleen and lymphoid organs, changes that are expected after immune stimulation. Virus was detected in a wide variety of tissues, including spleen, lymph nodes, the lining of the gastrointestinal tract, prostate, testis, cervix, vagina, and pancreas, but not* in others including brain, heart, kidney, and bladder. Different types of cells were infected in different tissues: lymphocytes in lymphoid organs, macrophages in lung, epithelial or interstitial cells in other organs. The authors note that “this viral behavior appears specific to this virus”.

Here are some other comments and conclusions drawn from this study:

  • The authors suggest that in Rhesus macaques, XMRV causes first an acute infection, followed by a persistent chronic infection. A persistent infection lasts for long periods of time; a chronic infection is a persistent infection that is eventually cleared. Since the monkeys in this study were all sacrificed, it’s not possible to determine if the infection was cleared.
  • The presence of XMRV in certain blood cells resembles the pattern in a cohort of ME/CFS patients
  • Virus is present in the prostate early in acute infection – XMRV was identified in prostate tumors
  • The presence of XMRV in reproductive tract tissues is consistent with sexual transmission of infection
  • After the acute phase, virus levels are very low, but there could be a different outcome in individuals with immune dysfunction
  • One animal produced virus after immunization; perhaps immune activation results in cycles of virus production
  • The virus has an initial acute phase followed by reactivation. The authors comment: “While our study has not linked XMRV infection with pathogenic mechanisms that might lead to prostate cancer or chronic fatigue syndrome, we submit that such link, assuming it exists, would be a temporally distant one.”
  • It would be informative to determine if XMRV is present in some of the same tissues in humans that were observed to be infected in rhesus macaques

Because the study involved only a small number of monkeys (8), the experiments should be repeated with additional animals, and in different laboratories, to verify the findings. I also wonder if the choice of the intravenous inoculation route had an effect on the pattern of infection and tropism. It is well known that viral pathogenesis can be determined by how the virus enters the host. For example, the same virus may replicate in different tissues, or have different virulence, when inoculated in different ways. This question can be readily addressed by inoculating rhesus macaques via different routes.

Studying viral pathogenesis (the series of events that occur during viral infection of a host) in animals is essential for understanding how viruses cause disease in humans. However, the results of such studies must always be interpreted with caution, because what is true in an animal is not always true for a human. For example, simple differences in size, metabolism, and development can have substantial effects on pathogenesis. In interpreting the results of animal studies, we must keep in mind the adage, ‘Mice lie, monkeys exaggerate‘.

Update: *These are the results of immunohistochemistry (IHC), which detects viral proteins and likely the produce of viral replication. When the IHC-negative tissues were examined for the presence of viral nucleic acids, low frequency signals were detected. The authors speculate that this is likely a consequence of failure of XMRV to replicate in these tissues.

Onlamoon, N, DasGupta, J, Sharma, P, Rogers, K, Suppiah, S, Rhea, J, Molinaro, RJ, Gaughan, C, Dong, B, Klein, E, Qui, X, Devare, S, Schochetman, G, Hackett, J, Silverman, R, & Villinger, F (2011). Infection, viral dissemination and antibody responses of Rhesus macaques exposed to the human gammaretrovirus XMRV Journal of Virology

Frank Fenner, MD, 1914-2010

Australian virologist Frank Fenner, MD was born in Ballarat, Victoria in 1914. He earned a Doctor of Medicine in 1942 at the University of Adelaide, and from 1940 – 1946 he worked on the malaria parasite in Egypt and Papua New Guinea as an officer in the Australian Army Medical Corps. He subsequently began studying the pathogenesis of mousepox virus at the Walter and Eliza Hall Institute of Medical Research in Melbourne. Later he was appointed Professor of Microbiology at the John Curtin School of Medical Research at the Australian National University, where he continued his work on viruses, including myxoma virus. His interest in the balance between virus virulence and host resistance was put to practical use in an effort to control Australia’s rabbit plague through the introduction of myxoma virus.

Dr. Fenner was a co-author of The Biology of Animal Viruses, first published in 1968. I still have my paperback ‘student’s edition’ which served as my virology bible during my years as a Ph.D. student. Later, when I was developing virology lectures for medical and graduate students, I relied on this book heavily. From the introduction:

During the last twenty years virology has developed into an independent science. It is now growing so rapidly that two new journals of virology were launched this year. Four major works on viruses of vertebrate animals have been published recently….However, none of these books deals in a comprehensive way with the broader biological principles of animal virology, which is the aim of this two-volume work.

The idea of presenting virology as a series of principles, not simply a list of viruses, was novel, and inspired us during the writing of Principles of Virology many years later.

Fenner’s classic studies on mousepox pathogenesis were the first to demonstrate how disseminated viral infections develop from local multiplication to primary and secondary viremia. In the case of mousepox, after local multiplication in the foot, the host response leads to swelling at the site of inoculation; after viremia, the host response to replication in the skin results in a rash. The figure at left depicting these events is included in Principles of Virology, because the findings serve as a paradigm for many other viral infections.

Fenner was also well known for his work on rabbitpox. European rabbits were introduced into Australia for hunting in 1859, and lacking natural predators, they reproduced to plague proportions. The rabbitpoxvirus, myxoma virus, was released in Australia in the 1950s in an attempt to rid the continent of these rabbits. In the first year, the infection killed the rabbits with a 99.8% mortality rate. By the second year the mortality dropped to 25%, and subsequently the rate of killing was lower than the reproductive rate of the rabbits, ending any hope for 100% eradication of the animals. The most important lesson from this incident is that the original idea to eliminate rabbits with a lethal virus was flawed, because powerful selective forces that could not be controlled or anticipated were at work. Fenner published a series of journal articles from 1950-1964 which carefully documented the changes in the virus and the host that occurred during this incident.

For more information on Dr. Fenner, see his interview from June of 2010 in The Australian, and a summary of his career at the Australian National University.

Fenner F (2010). Deliberate introduction of the European rabbit, Oryctolagus cuniculus, into Australia. Revue scientifique et technique (International Office of Epizootics), 29 (1), 103-11 PMID: 20617651

FENNER F, & WOODROOFE GM (1965). CHANGES IN THE VIRULENCE AND ANTIGENIC STRUCTURE OF STRAINS OF MYOMA VIRUS RECOVERED FROM AUSTRALIAN WILD RABBITS BETWEEN 1950 AND 1964. The Australian journal of experimental biology and medical science, 43, 359-70 PMID: 14343496

TWiP 11: One times three million

Hosts: Vincent Racaniello and Dickson Despommier

On episode 11 of the podcast “This Week in Parasitism”, Vincent and Dickson continue their discussion of malaria, with emphasis on clinical aspects of the disease.

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