Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Evolution in Action: Why Some Viruses Jump Species

17.03.2006


Researchers studying strains of a lethal canine virus and a related human virus have determined why the canine virus was able to spread so quickly from cats to dogs, and then from sick dogs to healthy dogs. Their studies may lead to a new understanding of the critical molecular factors that permit viruses to jump from one species to another — information that could be helpful in assessing how much of a threat avian influenza is to humans.



In advance online publication of a paper in the April 2006 issue of the Journal of Virology, Laura Shackelton, an HHMI predoctoral fellow at the University of Oxford in England, examined the surprisingly rapid evolution of the B19 erythrovirus, a ubiquitous human parvovirus.

Shackelton’s latest paper extends her previous research published in the Proceedings of the National Academy of Sciences in 2005 on the carnivore parvoviruses, specifically panleukopenia virus (FPLV), a feline virus that crossed over into dogs over 30 years ago. The work was done in collaboration with her advisor, former Oxford professor Edward C. Holmes, who is the senior author on the papers. Holmes recently moved his laboratory to Pennsylvania State University, where Shackelton will join him for postdoctoral research.


Shackelton’s work can be considered a genomic analysis of evolution in action. "Viruses don’t leave fossils," she explains. "But if you compare the differences between extant viral sequences, you can calibrate the molecular clock."

Viruses penetrate the interior of cells by binding to receptors on the host cell’s surface. The binding occurs in much the same way that a key fits into a lock. Sometimes proteins on the outer coat of a virus mutate enough to match the receptors on the cells of species other than ones that the virus usually infects. This is what has happened with avian flu. Once in a new species, the virus either dies out or is preserved and adds mutations that enable it to move from host to host within the new species. This can lead to widespread infection.

Shackelton wanted to understand the process of host-switching, the molecular mechanisms viruses employ to jump from one species to another. "We found the carnivore parvoviruses to be an excellent model for studying the molecular changes that accompany host-switching," she said, "because it’s one of the very few viruses for which we have adequate sequence data before and after the cross-species transfer."

Colin R. Parrish, a parvovirus expert at Cornell University, and Uwe Truyen of the University of Leipzig, co-authors on the PNAS paper, provided the genomic sequences of parvovirus stocks that dated back to the 1960s. Working with the sequences, Shackelton traced backwards to construct a phylogenetic tree showing when mutations in the virus became fixed and started being transmitted from generation to generation.

In order to estimate the evolutionary dynamics of the virus, she and Holmes used a Bayesian Markov Chain-Monte Carlo (MCMC) approach. A powerful statistical tool, the Bayesian MCMC method looks at probabilistic relationships. "This approach allows us to utilize the information in the viral sequences, and their isolation dates, to thoroughly explore models and modes of their molecular evolution," says Shackelton.

Their analysis showed that the version of the virus found in cats had been infecting the feline population for over one hundred years. But once it began to infect canines, FPLV, now canine parvovirus (CPV-2), quickly accumulated additional nucleotide substitutions, or changes in individual DNA building blocks, and gained the ability to transfer from an infected dog to a healthy dog. The rapid pace of that change contradicted conventional wisdom, which says that DNA viruses do not mutate rapidly.

Parvoviruses are single-stranded DNA viruses that package one strand of DNA in a protective shell, called a protein capsid. Once in the host cell, this strand acts as the template, and the virus replicates through a double-stranded intermediate. The more common double-stranded DNA viruses need to have the coiled helix unwind in order to replicate.

"Since they’re DNA viruses and replicate with host-cell machinery, it was just assumed that we should see rates of mutation more on par with those of their hosts and other DNA viruses," said Shackelton. "Instead, we were seeing orders-of-magnitude differences, rates more characteristic of RNA viruses."

Intrigued, she then set out to see if this phenomenon was characteristic of the entire Parvoviridae family. In the research reported in the Journal of Virology, she examined the human B19 erythrovirus, a parvovirus that infects bone marrow progenitor cells and can be associated with heart complications. She chose it because it is distantly related to CPV-2, with different routes of infection. The analysis showed the same surprisingly rapid rate of change. She and Holmes are now confident that "the difference between DNA and RNA viruses is not as simple as we thought it was. There’s something unique about parvoviruses that possibly extends to all single-strand viruses."

In their next series of experiments, together with Parrish’s group, the scientists will work to understand more about that uniqueness and learn its underlying cause. It is work that may help in understanding all viruses, including avian flu.

"The more we know about species transfer events and factors influencing nucleotide substitution rates, the better," says Shackelton, who is also interested in public policy responses to viral outbreaks, "This work is increasing our knowledge about what molecular changes need to happen for species transfer, which changes or combinations of changes are the critical ones, and how frequently they occur."

Jennifer Donovan | EurekAlert!
Further information:
http://www.hhmi.org

More articles from Life Sciences:

nachricht Fish Oil-Diet Benefits May be Mediated by Gut Microbes
28.08.2015 | University of Gothenburg

nachricht Bio-fabrication of Artificial Blood Vessels with Laser Light
28.08.2015 | Fraunhofer-Institut für Lasertechnik ILT

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

Im Focus: What would a tsunami in the Mediterranean look like?

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal areas in southern Italy and Greece. The study is published today (27 August) in Ocean Science, an open access journal of the European Geosciences Union (EGU).

Though not as frequent as in the Pacific and Indian oceans, tsunamis also occur in the Mediterranean, mainly due to earthquakes generated when the African...

Im Focus: Self-healing landscape: landslides after earthquake

In mountainous regions earthquakes often cause strong landslides, which can be exacerbated by heavy rain. However, after an initial increase, the frequency of these mass wasting events, often enormous and dangerous, declines, in fact independently of meteorological events and aftershocks.

These new findings are presented by a German-Franco-Japanese team of geoscientists in the current issue of the journal Geology, under the lead of the GFZ...

Im Focus: FIC Proteins Send Bacteria Into Hibernation

Bacteria do not cease to amaze us with their survival strategies. A research team from the University of Basel's Biozentrum has now discovered how bacteria enter a sleep mode using a so-called FIC toxin. In the current issue of “Cell Reports”, the scientists describe the mechanism of action and also explain why their discovery provides new insights into the evolution of pathogens.

For many poisons there are antidotes which neutralize their toxic effect. Toxin-antitoxin systems in bacteria work in a similar manner: As long as a cell...

Im Focus: Fraunhofer IPA develops prototype of intelligent care cart

It comes when called, bringing care utensils with it and recording how they are used: Fraunhofer IPA is developing an intelligent care cart that provides care staff with physical and informational support in their day-to-day work. The scientists at Fraunhofer IPA have now completed a first prototype. In doing so, they are continuing in their efforts to improve working conditions in the care sector and are developing solutions designed to address the challenges of demographic change.

Technical assistance systems can improve the difficult working conditions in residential nursing homes and hospitals by helping the staff in their work and...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

Large agribusiness management strategies

19.08.2015 | Event News

 
Latest News

Interstellar seeds could create oases of life

28.08.2015 | Physics and Astronomy

An ounce of prevention: Research advances on 'scourge' of transplant wards

28.08.2015 | Health and Medicine

Fish Oil-Diet Benefits May be Mediated by Gut Microbes

28.08.2015 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>