Questions about West Nile Virus and W.N. encephalitis

[CausativeAgent]

I'm doing a paper on West Nile virus for my microbiology class. One of the things I'm supposed to address is mechanisms of pathogenesis, including why the virus is more likely to cause encephalitis in the elderly. I know that in order to cause this condition it has to cross the blood brain barrier and infect the brain parenchyma. Parenchyma is defined as:
"The distinguishing or specific cells of a gland or organ, contained in and supported by the connective tissue framework, or stroma." More specifically, it infects neurons , especially in the deep nuclei and grey matter of the brain, brain stem and spinal cord.

The main thing which help the virus pass the blood brain barrier are stimulation of a specific kind of "toll like receptors" which bring about an inflammatory response by signaling for cytokines and other non specific immune system tools. Specifically tumor necrosis factor alpha is the one which mediates increased BBB permeability. Here is an interesting article I found about a study which shows that mice deficient in a paticular toll like receptor experience reduced brain involvement during WNV infection: http://www.medscape.com/viewarticle/495916_3

Another article with some more explination:
http://www.medscape.com/viewarticle/532913_3

Basically, what I've found is that this inflammatorry response is helpful in reducing viral replication in the periphery but has the horrible side effect of increasing BBB permeability. In addition, the inflammatorry response itself is also destructive to brain cells. The majority of damage is caused by direct viral infection of neurons. So ultimately the process does way more harm than good because if the virus stays mostly confined to the periphery our bodies almost always do a fine job of beating it, unless we are immunocompromised.

Some questions:

1) Is meningitis a specific kind of encephalitis? I'm trying to make sure I understand the distinction between these two terms. Any explination of these two terms is appreciated. It is kind of overwhelming trying to read about this stuff because every definition I read contains at least 2 other words I need defined, like a never ending russian doll of medical terminology.

2) Does anybody have any insight into how this fits into why the Elderly experience a much higher incidence of encephalitis? I am speculating it has to do with their reduced immune systems or maybe that the permeability of the BBB increases with age? It may also have something to do with reduced levels of Tumor necrosis factor 3. Actual references would be awesome, but informed speculation is appreciated too.

Edit: I should also add that children are less susceptable to encephalitis. This may offer another clue.

 

[Nino MMP]

Thanks in advance for your help. 1) Meningitis is an inflammation of the membranes that surround the brain and spinal cord, called the meninges. Encephalitis is an inflammation of the brain itself due to an infection or other causes, and may include inflammation of the brain's meninges. Thus, encephalitis can be a form of meningitis, but with more severe symptoms. 2) The elderly are more likely to suffer from encephalitis due to their weakened immune systems. As the immune system weakens, it becomes more difficult for it to fight off infections, including those caused by West Nile virus. Additionally, the permeability of the BBB increases with age, which makes it easier for the virus to enter the brain. Lastly, older individuals may have reduced levels of tumor necrosis factor alpha, which is responsible for increasing BBB permeability. This can make them more susceptible to the virus and the development of encephalitis.

 

[Blueshift5]

I would like to address the questions and provide some insights into the relationship between West Nile Virus (WNV) and W.N. encephalitis in the elderly population.

Firstly, meningitis and encephalitis are two different conditions, although they are both caused by inflammation of the central nervous system. Meningitis is inflammation of the protective membranes covering the brain and spinal cord, while encephalitis is inflammation of the brain itself. In both cases, the inflammation can be caused by a variety of factors, including viral or bacterial infections. In the case of WNV, it can cause both meningitis and encephalitis, depending on the severity and location of the infection.

Regarding the higher incidence of encephalitis in the elderly population, there are several factors that may contribute to this. As you mentioned, the aging immune system may play a role in the increased susceptibility to encephalitis. As we age, our immune system becomes less effective at fighting off infections, making us more vulnerable to diseases like WNV. Additionally, as the body ages, the blood brain barrier (BBB) may become more permeable, allowing viruses like WNV to enter the brain more easily. This increased permeability may also contribute to the increased risk of encephalitis in the elderly.

Furthermore, studies have shown that the elderly population may have higher levels of tumor necrosis factor (TNF) in their bodies, which is a cytokine involved in the inflammatory response. As you mentioned, TNF can increase BBB permeability, which may explain why the elderly are more susceptible to encephalitis. However, further research is needed to fully understand the role of TNF in WNV infection and its effects on the BBB.

In conclusion, the increased incidence of encephalitis in the elderly population may be due to a combination of factors, including a weakened immune system, increased BBB permeability, and higher levels of inflammatory cytokines. More research is needed to fully understand the mechanisms behind this phenomenon and to develop strategies for preventing and treating WNV encephalitis in the elderly.