A team of scientists from the Washington University School of Medicine in St. Louis and Utah State University have found a possible explanation to a puzzling and serious complication caused by a West Nile Virus infection. The researchers have shown that how the West Nile virus spread from nerve cell to nerve cell has a lot to do with triggering acute flaccid paralysis, a condition that leaves one or more limbs of an individual infected with the West Nile virus limp and unresponsive.

Studies made by the researchers showed that the West Nile virus can enter a nerve cell, replicate itself and then move on to other nearby nerve cells. Viruses that go through this pathway can get into the central nervous system and may trigger acute flaccid paralysis. As of now there is now current treatment to cure the condition apart from rehabilitation to relearn the use of the affected limb.

Senior author of the study, Michael Diamond, M.D., Ph.D., and an associate professor of molecular microbiology, of pathology and immunology and of medicine, said that the research was done to find an answer to the puzzling contrast that the West Nile virus infection may have on the central nervous system. In experiments that were led by Melanie Samuel, a graduate student from Dr. Diamond’s lab, the researchers found out that the virus can spread in either direction along the branches of neurons in a cell culture. They observed that the virus can travel down in nerve branches in small capsules known as vesicles. The researchers also found out that the infected nerve cells also releasing the virus.

In testing their observations in an animal model, the researchers used a suture to close off the sciatic nerve in hamsters. The West Nile virus was then directly injected into the nerve, either above or below the said suture. Animals that were injected with the virus below the suture came down with encephalitis while those injected with the virus above the suture develop both encephalitis and paralysis. The reason for this was that the virus was able to follow the sciatic nerve back to the central nervous system.

An infection that may lead to paralysis may not require high level of infection as that require by a West Nile infection that leads to encephalitis. It can happen as an infected mosquito bites a person and the virus is able to replicate somewhere in the area of the nerve. A small amount of the virus may be following the nerve back to the spinal cord even though the immune system may have cleared out the infection in the skin. This might lead to paralysis.

Source: http://www.sciencedaily.com/releases/2007/10/071018132950.htm

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