West Nile Virus Connected To Memory Loss, Again

The West Nile virus may be far more serious than previously understood. And, the most serious complication, may be a source of memory loss.

Spread by the bite of a mosquito, West Nile virus can cause fever and sometimes brain infections, known as West Nile encephalitis.

About half the people who survive the encephalitis are left with permanent neurological problems, such as memory loss.

As of January 9, 2018, 47 states and the District of Columbia have reported 2,002 West Nile virus infections to the Centers for Disease Control and Prevention (CDC)  in 2017. Of these, 67 percent were classified as neuroinvasive diseases, such as meningitis or encephalitis.

A new mice study suggests that these ongoing neurological deficits (memory loss) may be due to brain inflammation.

And when the inflammation is reduced by an arthritis drug, the mice appeared to regain their mental memory ability.

Robyn Klein, MD, Ph.D., a professor of medicine at Washington University School of Medicine said: “This is a proof of concept study that a drug can prevent cognitive impairments caused by viral encephalitis.”

Dr. Klein commented, “It may turn out that IL-1 is not a feasible target during viral infections, but these findings could lead to new therapeutic targets that are less problematic for clearing virus or to therapies for neurologic diseases of memory impairment that are not caused by viruses.”

Interleukin-1 is made mainly by one type of white blood cell, the macrophage, and helps another type of white blood cell, the lymphocyte, fight infections. It also helps leukocytes pass through blood vessel walls to sites of infection and causes fever by affecting areas of the brain that control body temperature.

Dr. Klein and colleagues had shown in 2016 that during West Nile encephalitis, the patient’s own immune system destroys parts of neurons, leading to memory problems.

Additionally, a 10-year study from researchers at Baylor College of Medicine was the first to link neurological problems associated with the West Nile disease, like memory impairments, to physical evidence of brain damage, as seen via magnetic resonance imaging.

The Baylor researchers found that mice infected with West Nile had a difficult time negotiating their way out of a maze. They later discovered that the infected mice suffered significant damage to their synapses.

When these scientists examined brain tissue from humans who had died from West Nile, they found the same phenomenon.

"Our findings add to a growing amount of evidence that West Nile virus is a serious health threat that deserves considerably more attention," said Kristy Murray, DVM, Ph.D., of Baylor's National School of Tropical Medicine and the lead author of the study.

This is because “there still are no drugs available to treat it and no vaccines to prevent West Nile,” said Dr. Murray.

Fortunately, most people infected with West Nile do not have symptoms. Only 20 percent of people who are infected develop serious symptoms, which include high fever, headache, neck stiffness, lack of energy, disorientation, coma, tremors, convulsions, muscle weakness, vision loss, numbness, and paralysis, says the CDC.

Visit the CDC Travel Alert site for updated location information.

The Washington University study was supported by the National Institutes of Health (NIH), grant numbers U19 AI083019, R01 NS052632 and HDTRA11510032; National Institute of Arthritis and Musculoskeletal and Skin Diseases, grant number P30AR048335; and the Speed Congenics Facility of the Rheumatic Diseases Core Center (experimental support).

Washington University School of Medicine is one of the leading medical research, teaching and patient-care institutions in the nation. Judy Martin Finch, Director of Media Relations, [email protected]