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5 December 2013 11:26 am ,
Vol. 342 ,
Researchers have been hot on the trail of the elusive Denisovans, a type of ancient human known only by their DNA and...
Thousands of scientists in the Russian Academy of Sciences (RAS) are about to lose their jobs as a result of the...
Dyslexia, a learning disability that hinders reading, hasn't been associated with deficits in vision, hearing, or...
Exotic, elusive, and dangerous, snakes have fascinated humankind for millennia. They can be hard to find, yet their...
Researchers have sequenced and analyzed the first two snake genomes, which represent two evolutionary extremes. The...
Snake venoms are remarkably complex mixtures that can stun or kill prey within minutes. But more and more researchers...
At age 30, Dutch biologist Freek Vonk has built up a respectable career as a snake scientist. But in his home country,...
Since arriving on the island of Guam in the 1940s, the brown tree snake ( Boiga irregularis ) has extirpated native...
- 5 December 2013 11:26 am , Vol. 342 , #6163
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Herpes Never Sleeps
18 November 2009 (All day)
Genital herpes comes and goes--at least that's what it looks like to patients. But a mathematical model published in the 18 November issue of Science Translational Medicine suggests that herpes never slumbers. Instead, nerve cells continuously pump out the virus in minuscule quantities over a sufferer's lifetime. If the findings hold, it may be much harder to stop patients from passing on the infection than researchers thought.
As many as one in five people is permanently infected with herpes simplex virus 2 (HSV-2), the most common cause of genital skin ulcers. The virus is transmitted during sex; after infection, it retreats into nerve cells that have their endings in the genital skin. HSV-2 causes no problems in up to 80% of those infected, but a minority suffers from blisters and sores once or twice a month. For decades, most scientists believed that the virus was simply "off" in the intervals between outbreaks, says William Halford, who studies herpes at Southern Illinois University School of Medicine in Springfield.
But that view has come under fire the past decade or so, as researchers showed that the virus is sometimes present in the genital skin even when no lesions are apparent. The new work, by infectious diseases researcher Lawrence Corey and his colleagues at the University of Washington and the Fred Hutchison Cancer Research Center, both in Seattle, goes even further.
Joshua Schiffer, a clinician and mathematical modeler in Corey's group, constructed mathematical models from a large amount of virological and patient data--including the amount of virus present in the skin of patients who took four swabs daily for 60 days. This is what appears to be going on: Nerve cells shed tiny amounts of virus almost constantly inside the genital skin. Frequently, a virus will infect an epithelial cell, which compared with a nerve cells are "real virus factories," says Schiffer: They produce massive amounts of virus that can infect other nearby epithelial cells and can presumably also infect sexual partners. In most cases, infected epithelial cells are quickly killed by CD8+ cells, a type of white blood cells; only occasionally does the infection overwhelm the immune system, resulting in a lesion.
"It's impressive that they were able to build a model that makes sense of a large amount of clinical data," says Philip Krause, a herpes researcher at the U.S. Food and Drug Administration. "It's a very thoughtful way of looking at the data." Halford says the paper should help dispel the notion, still supported by many herpes scientists, that the virus "does nothing" between clinical episodes.
The findings may also explain some properties of antiherpes drugs like acyclovir, says Schiffer. For instance, in a trial where herpes patients took acyclovir to prevent their partners from becoming infected, the drug was only 50% effective. If virus shedding never stops, these drugs have a much harder job, says Schiffer, especially compounds like acyclovir that quickly disappear from a patient's body. To really prevent transmission, drugs would have to last longer or stop the shedding by the nerve cells, he adds--but that's a tall order.