Saturday, June 6, 2015

Contagiousness of MERS

The recent outbreak of MERS - Middle East respiratory syndrome virus - has infected at least 36 people in South Korea.  As a result, the outbreak has been a source of concern for epidemiologists around the world.  Efforts to quarantine people and camels have followed in an attempt to squash the outbreak.

Perhaps surprisingly, however, the MERS virus is not highly contagious; previous studies have found that its R0 is 2-3, meaning that the average infected person only infects two to three other people.  In fact, MERS is thought to be spread primarily zoonotically (from camels to humans).

It is important to note that while the MERS virus is not highly contagious, it is still important to monitor the outbreak and prevent it from growing any larger.  One issue commonly found in reports on the contagiousness of viruses is that there is an implication that less contagious viruses cannot manifest into epidemics and that they are less serious than highly contagious viruses.  However, with HIV - a virus that is relatively low in contagion (e.g. exposure to the virus via an infected needlestick seldom leads to infection) - we see that it can still lead to a deadly epidemic.  More recently, Ebola, a virus with an R0 if 1.5-2.5 manifested itself into the huge Ebola outbreak in West Africa.

Thus, articles reporting on the contagiousness of viruses should be taken just as a presentation of the facts, or as one of many indicators of the epidemic potential of a virus.


--Andrew Duong

Thursday, June 4, 2015

Inexpensive Blood Test Reveals Your Viral Exposure History?

A international team of scientists has just developed a comprehensive screening mechanism called VirScan. This technology is a high-throughput method that comprehensively analyzes antiviral antibodies using immunoprecipittion and parallel DNA sequencing of a bacteriophage library that displays proteome-wide peptides from all known human viruses. While it might not be a complete history, VirScan revealed the presence of antibodies to 10 or more different viral species per person in a 569-person study that included subjects from the United States, Peru, Thailand, and South Africa. At least two of the individuals tested had at least antibodies against 84 different viral species. The study found 206 different viral species in total, and over 1000 strains.
            Widespread adoption of VirScan could be a great diagnostic and research tool. Current serological testing is usually focused on testing for one pathogen at a time. The analysis costs about $25 per person and only 1 microliter of blood. One of the unexpected results of VirScan was that different people produced structurally similar antibodies to a small number of “public” epitopes for many different viral species. The team hopes that VirScan can be used to study the effect of host-virome interactions on human health, and possibly be expanded for test for bacterial, fungal, and protozoan pathogens.
            Clinically, VirScan could be used to identify antibodies for a virus that a patient might not be aware he/she was exposed to, especially latent viruses that can lead to cancer (e.g. hepatitis C). VirScan could also be used to draw associations between viruses and chronic conditions such as diabetes and chronic fatigue syndrome.

 The color of each cell in the grid depicts the relative number of antigenic epitopes detected for a virus (rows) in each sample (column).

Other Sources:


Wednesday, June 3, 2015

A New Way to Look at Viruses—Weighing by Mass Spectrometry

            There are various techniques that have been used over the years to study viruses. Scientists have studied their pathological effects in living systems, their cytopathic effects in cell culture. We can directly observe viruses through x-ray crystallography.

Pathological Approach:
 Varicella-zoster virus is one of a myriad of viruses that causes distinctive signs and symptoms/pathologies. The body’s immune response to the varicella-zoster virus causes the characteristic red spots of chickenpox. The list goes on. Macroscopic diagnoses can be used in epidemiological studies and for diagnostic purposes. Before the development of modern laboratory and imaging techniques, this was how many viral illnesses were first characterized.

Cytopathic Effect:
Characteristic deformities that certain viruses cause to the cells they infect. For example, some herpes viruses cause multinucleation. Respiratory syncytia virus (Paramyxoviridae) causes syncytia (fusion of multiple cells into one large one).

--multinucleation (wikimedia commons)

X-Ray Crystallography:
Was used to produce the first pictures of DNA--it involves studying the diffractions of x-rays from crystalline atoms.

--X-ray crystallography of Poliovirus type 1

Scanning Electron Microscopy:

Scanning electron microscopes produce 3-dimensional images. They can show topographical details of a virus.


Transmission Electron Microscopy:

TEM has a higher magnification and greater resolution, but produces 2-dimensional rather than 3-dimensional images.

However, there has just been a study to use a different imaging technique to study viruses: mass spectrometry. For the first time ever, we can weigh an intact virus. Specifically, the study used heavy-ion mass spectrometry MS to study a mixture of intact virus particles. The team, led by Carnegie Mellon University’s Mark Bier and his graduate student Logan Plath, used samples containing two varieties of a cowpea (black-eyed pea) mosaic virus (a plant virus); they found that one virus weighted 5.65 megadaltons, and the other 4.84 megadaltons. Both of these numbers were approximately that of the theorized masses of the viruses.
Previously, mass spectrometry’s use in virology has been limited because intact viruses have been too large. To get around this problem, Bier’s group used a cryodetector-based matrix-assisted laser desorption/ionization time of flight mass spectrometer (that’s a real mouthful), called a Macromizer. The 3.75 meter-long apparatus can analyze low charge heavy ions with greater sensitivity than standard mass spectrometers.

--black-eyed pea mosaic virus--what's it gonna do with all those megadaltons inside that trunk?