"Nobody really knows why flu is a winter disease in the temperate regions and more continuous in the tropics," says Edward Holmes, professor of biology at Penn State. "The big question is, ‘Why is flu seasonal"’"
Flu infections in the Northern Hemisphere typically follow a familiar pattern. Some time before the start of the winter infection season, the virus evolves, changing enough to evade the previously primed immune system. Then, just before summer, the virus disappears, only to resurface the next fall with a completely different genetic makeup, ready to fool the immune system anew.
But little is known about what happens to the virus between two successive winters, or how and where it is able to sustain itself.
The key question, Holmes explains, is whether the virus settles into a dormant state waiting for the right cues of temperature and sunlight to reactivate, or whether it migrates to viral reservoirs in the tropics, from where it is later reintroduced.
It is thought that places in Southeast Asia, where humans and animals live in close proximity, might be the permanent melting pot where viruses continually circulate and exchange genetic information.
To test the migration theory, Holmes and Martha Nelson, graduate student at Penn State, and their colleagues at the National Institutes of Health, Lone Simonsen, Cecile Viboud, and Mark A. Miller, analyzed the influenza A virus genomes of 900 virus samples from New Zealand, Australia and New York state dating between 1998-2005.
Their findings, outlined in this month's issue of PLoS Pathogens, reveal that the genomes of 52 viruses from New York are closely related to viruses that circulate during the winter (April to October) in New Zealand and Australia. These mixed family trees of viruses from both the north and south suggest there is widespread viral traffic across the equator each season, which contributes significantly to new epidemics in both hemispheres, the researchers note.
"If the viruses had been dormant, samples from successive seasons in each region would only be closely related to other viruses of that same region," said Holmes, who is also affiliated with Penn State's Center for Infectious Disease Dynamics (CIDD). "The fact that they are, instead, interspersed clearly tells us that the viruses are seasonally migrating across both hemispheres."
However, it is still fully unclear where and when the viruses are evolving to beat the immune system. According to Nelson, the virus changes its entire genetic makeup somewhere during the summer off-season, and it likely does this in the tropics, where the virus is found year-round.
"But we cannot say for sure at this point. To test this theory, we need viral samples from the tropics," Nelson added. The authors anticipate that samples from these regions will become available in the next few years.
The researchers are also not sure why the virus seems to die out during summer and what exactly triggers its return.
"It could be anything from human migration, aspects of climate, levels of sunlight, seasonal susceptibility of people or a combination of all these and more factors. That is another big question," said Holmes, whose work is funded by the National Institutes of Health.
What is certain, the Penn State researcher noted, is that multiple viruses arrive in New York state each season. In a connected world where emerging viruses can spread globally very quickly, Holmes says that the best way to protect communities is to have an extremely good system of disease surveillance in place and to develop universal vaccines that can protect against all kinds of influenza virus.
Scientists enlist engineered protein to battle the MERS virus
22.05.2017 | University of Toronto
Insight into enzyme's 3-D structure could cut biofuel costs
19.05.2017 | DOE/Los Alamos National Laboratory
Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.
Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...
An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...
In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.
In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...
Dental plaque and the viscous brown slime in drainpipes are two familiar examples of bacterial biofilms. Removing such bacterial depositions from surfaces is...
For the first time, scientists have succeeded in studying the strength of hydrogen bonds in a single molecule using an atomic force microscope. Researchers from the University of Basel’s Swiss Nanoscience Institute network have reported the results in the journal Science Advances.
Hydrogen is the most common element in the universe and is an integral part of almost all organic compounds. Molecules and sections of macromolecules are...
22.05.2017 | Event News
17.05.2017 | Event News
16.05.2017 | Event News
22.05.2017 | Materials Sciences
22.05.2017 | Life Sciences
22.05.2017 | Physics and Astronomy