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Memory loss caused by West Nile virus explained

Dolphin

Senior Member
Messages
17,567
ME/CFS can often follow an infection and I've heard descriptions of the long-term effects of West Nile virus that sounded similar enough to ME/CFS and so possibly of relevance/interest.

https://medicine.wustl.edu/news/memory-loss-caused-west-nile-virus-explained/


Memory loss caused by West Nile virus explained
Study identifies targets for prevention, treatment

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CDC/ James Gathany
Thousands of people live with memory loss and other long-term neurological problems as a result of infection with West Nile virus, which is spread by mosquitoes. Researchers at Washington University School of Medicine in St. Louis have shown that these problems may be due to the patients' own immune systems destroying parts of the neurons in the brain, which suggests that intervening in the immune response may help prevent brain damage so patients can recover.

Every year as mosquito season arrives, so does West Nile virus, causing fever in thousands of people nationwide and life-threatening brain infections in an unlucky few. About half the people who survive that infection – West Nile encephalitis – are left with permanent neurological deficits such as memory loss.

New research shows that these long-term neurological problems may be due to the patient’s own immune system destroying parts of the neurons in the brain, which suggests that intervening in the immune response may help prevent brain damage so patients can recover.

The study is published June 22 in Nature.

West Nile was first identified in the Western Hemisphere in 1999, when groups of birds began dying in New York and a veterinary pathologist at the Bronx Zoo brought the deaths to the attention of the Centers for Disease Control and Prevention. The virus has since spread throughout the Americas, infecting millions of people. Ten thousand West Nile survivors are living with long-term neurological problems such as fatigue, weakness, difficulty walking and memory loss, and the number goes up by about 1,000 every year following mosquito season. There is no vaccine or specific treatment for West Nile infection.

“When I talk with other doctors about West Nile patients with these persistent neurological deficits, many say, ‘The virus in their brains must have killed neurons, and there’s nothing we can do about it,’” said Robyn Klein, MD, PhD, a professor of medicine and the study’s senior author. “My thinking has been, if we can determine what triggers this brain damage, maybe we can prevent it from happening or stop it afterwards.’”

Klein, postdoctoral researcher Michael Vasek, PhD, and colleagues developed a mouse model of West Nile encephalitis by injecting a weakened strain of the virus directly on top of the mouse hippocampus, a region of the brain important for memory. A month after the mice had recovered from the infection, the researchers tested the animals’ ability to navigate a maze.

Much like West Nile survivors who cannot navigate their neighborhoods, the infected mice could not remember how to navigate the maze. But contrary to conventional wisdom, their hippocampal neurons hadn’t been killed by the virus.

Instead, the researchers found that microglial cells, a kind of immune cell that lives in the brain, were clustered around the neurons at the site of infection and were highly activated – “on fire,” as Klein put it.

Moreover, levels of an immune protein called complement were high in the brains of mice with memory loss. Neurons make connections to each other at junctions called synapses, allowing information to be passed from cell to cell. During normal brain development, many more synapses are formed than needed and only those that are strengthened should persist. Complement tags the weak synapses to be removed, and the activated microglia destroy them.

In the mice with memory loss, viral infection seemed to have sent this system into overdrive, leading to the destruction of necessary synapses. Synapses must be formed or strengthened for learning and memory to occur. While the neurons near the activated microglia were still alive, they lacked synapses. The more synapses that were destroyed, the worse the mouse’s memory problems.

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Robert Boston
Robyn Klein, MD, PhD, and Michael Vasek, PhD, examine images of mouse synapses. The researchers found that memory loss suffered by some survivors of West Nile encephalitis may be caused by the loss of synapses between neurons.
“There’s never been any model of cognitive dysfunction due to brain infection that shows that eliminating synapses without loss of neurons could cause these symptoms,” said Klein, who is also a professor of pathology and immunology, and of neuroscience. “It’s really a paradigm-shifting idea that a viral infection can do this. It also makes us wonder whether these mechanisms are involved in other diseases associated with memory loss.”

Healthy people create new synapses throughout life as they learn new things. West Nile survivors, however, may be unable to grow new synapses to replace the ones lost during their bouts of encephalitis.

“The microglia remain activated long after the virus is cleared, and this may be preventing the synapses from recovering,” Klein said. “But that gives us hope that we can develop interventions directed at the immune response. We think we can treat this, and that’s what we’re trying to do.”

Update: Details in this news release regarding how West Nile virus first was identified in the Western Hemisphere have been corrected.


Vasek MJ, Garber C, Dorsey D, Durrant DM, Bollman B, Soung A, Yu J, Perez-torres C, Frouin A, Wilton DK, Funk K, DeMasters BK, Jiang X, Bowen JR, Mennerick S, Robinson JK, Garbow JR, Tyler KL, Suthar MS, Schmidt RE, Stevens B, Klein RS. A complement-microglial axis drives synapse loss during virus-induced memory impairment. Nature. June 22, 2016.

Funding for this research was provided by the National Institutes of Health (NIH), grant numbers F31 NS077640, R01 NS052632 and U19 AI083019.

Washington University School of Medicine‘s 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children’s hospitals. The School of Medicine is one of the leading medical research, teaching and patient-care institutions in the nation, currently ranked sixth in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children’s hospitals, the School of Medicine is linked to BJC HealthCare.
 
Last edited:

Simon

Senior Member
Messages
3,789
Location
Monmouth, UK
Interesting stuff.

West Nile was first identified in the Western Hemisphere in 1999,
FWIW, that was Ian Lipkin

Dr. W. Ian Lipkin, Virus-Hunting Master - The New York Times (Carl Zimmer piece)
As Dr. Lipkin earned his reputation as a virus hunter, other researchers began to bring difficult cases to him. In 1999, for example, doctors noticed a cluster of cases of encephalitis around New York City. They shipped blood from their patients to Dr. Lipkin, who was then at the University of California, Irvine. Analyzing the genetic material, he and his colleagues concluded that the encephalitis had been caused by West Nile virus. It was the first time the virus had been identified in the Western Hemisphere.
 

Hip

Senior Member
Messages
17,824
So this is what the West Nile virus study says is happening in the brains of mice:

(1) There are high levels of complement system molecules in the brains of these mice with West Nile virus infection. The study says that complement C3 and C3a receptors are involved.

(2) The hippocampal microglia were highly activated by the West Nile virus infection.

(3) Normally, complement molecules tag synapses that are not required, and once tagged, it is the job of microglia to delete and remove the unwanted tagged synapse.

(4) However, because both the level of the complement molecules and the level of microglial activation is high in these infected mice brains, too many synapses get deleted, leading to memory problems, because new synapses must be formed or strengthened for learning and memory to occur.



It is interesting that complement C4a is activated by exercise in ME/CFS. Ref: 1

And C4a is active in Lyme disease. Ref: 1

Erythropoietin (EPO, Procrit) lowers C4a, see this article.

More info: Intro to C4A (Complement Component 4 A) and Its Role in CFS, Mold, and Histamine Intolerance

Not sure if this C4a activation in ME/CFS and Lyme might relate to the synaptic deletion found in the West Nile virus study.