[0:00]Hey everyone, welcome to another lesson. In this lesson we're talking about the West Nile virus. So, we're going to talk about how we become infected with this virus, we're also going to talk about signs and symptoms, how we can diagnose it, how we can treat it, and how we can try to prevent becoming infected. So, the West Nile virus is a virus in the viral family Flaviviridae. It is a flavivirus. So, it's in the same family of viruses like the dengue viruses. And it is also a member of the Japanese encephalitis virus antigenic complex. We're going to talk about the Japanese encephalitis virus in another lesson. Like the other flavoviruses, it is a positive-sense single-stranded RNA virus. And the West Nile virus is important to understand because infection with this virus can cause encephalitis or inflammation of the brain. We're going to talk about this in more detail in the next couple of slides. And this virus is named after the place where it was first discovered. It was actually first discovered in the West Nile province of Uganda in 1937. So, we can see here on the map, here is Uganda, and the West Nile province is up in the northwest of the country. And although it was spread and caused infections in several countries for years, it became more recognized and talked about in the late 1990s. And in fact, in 1999, it was introduced to the United States, and that's when we saw about 62 cases of encephalitis, and 7 deaths in the United States. And the virus is now considered endemic to North America, which means that it's not coming from other continents. It's actually here being transmitted through its vector and host. We're going to talk about that in the next slide. So, how is it transmitted? So, the transmission of the West Nile virus occurs primarily through birds. So, birds are the primary host for the West Nile virus. And the birds in particular are crows and blue jays. And what happens is there's a mosquito that comes around and bites and feeds on the bird that is carrying the virus. And when that mosquito picks up the virus from an infected bird, it becomes a vector and transmits the virus to other crows and blue jays, transmitting and propagating the virus. And we see this occurring with mosquitoes of the Culex species. And this is the reason why the West Nile virus is known as an arbovirus. And an arbovirus simply means that it is a virus spread through arthropods. So, arthropods like insects, like mosquitoes. So, an infected mosquito can not only infect other birds, but it can actually bite and infect humans. And this is why this is important in areas where there are bird deaths and where there is known West Nile virus infections in blue jays and crows. These mosquitoes can pick up the virus and transmit it to humans. And when a person becomes infected with the West Nile virus from a mosquito bite, that person can transmit the virus to other people, and it occurs through vertical and horizontal transmission. So, what is vertical transmission? So, vertical transmission is from one generation to another, so from mother to fetus. So, there is mother-to-fetus transmission, that is possible. And horizontal transmission is basically everything else. So, horizontal transmission, you can think of it through blood transfusions and organ transplants. So, you can theoretically take the blood out of an infected person and transfuse it into another person, and you could infect another person that way, or you could take an organ from an infected individual and transplant it into an uninfected individual, leading to an infection. This can occur, but it is very, very rare. So now that we know how it's transmitted, what actually happens when a mosquito carrying the West Nile virus bites a person? So, if a mosquito bites an individual, and that mosquito is carrying the virus, that virus can enter into the person's tissues from the mosquito's saliva. And the virus can then multiply in the skin of the individual. That is called the early phase of infection. Eventually what happens is the virus continues to multiply and enters into the bloodstream. And that is what we call viremia, virus in the blood. And the virus not only enters the blood, but it can also enter into regional lymph nodes and into the spleen, so the lymphatic system.
[4:18]And then in some cases, very rarely, but in some cases, the virus can actually enter into the central nervous system, into the brain. And this is what we call the central nervous system phase. So, individuals who are infected with the West Nile virus don't necessarily have to go through each of these phases. They don't have to necessarily go through all of these phases. They might just make it into the early phase or into the visceral organ dissemination phase. And a small subset, a very small subset will enter into this phase. So, what are some of the clinical features of the West Nile virus? What happens when an individual becomes infected with this virus? So, there's an incubation period that is roughly anywhere from 2 to 14 days, so it's quite variable. But what's important to recognize is that a majority of people that are infected with this virus are asymptomatic. There is no symptoms. And symptoms actually only occur in about 20 to 40% of infected people. So, it's actually a minority of people that have symptoms when they become infected with this virus. One of the big symptoms is fever. So, if they are to be symptomatic, they're likely to have a fever. And we call this a West Nile fever. And this occurs in about a quarter of infected patients, so 25%. And for whatever reason, women are more at risk for getting a fever in the West Nile virus infection. Other symptoms include a headache, which usually occurs abruptly, so it's an acute onset of a headache. We can also see myalgias or muscle aches and pains. So, these symptoms, fever, headache, and myalgias are very common among other viral infections as well. So, they're non-specific symptoms. But we can also see back pain in the West Nile virus infection, which is a bit more specific with regards to this viral infection. We can also see anorexia, so they don't have much of an appetite, and we can see a maculopapular rash, which again is not very specific for West Nile virus infections. Other viral infections can lead to similar rashes.
[6:25]And this seems to occur in about 25 to 50% of cases. Other clinical features of a West Nile virus infection include nausea, vomiting, and diarrhea. So, individuals can have gastrointestinal upset with a West Nile virus infection. They can also have accompanying abdominal pain, and they can also have pharyngitis, so a sore throat. So, you can see here, here's a pharynx that is quite red or erythematous. So, it can appear like an upper respiratory tract infection. But what's very important to recognize with the West Nile virus infection is that it can lead to neuroinvasive disease, a neuroinvasive West Nile disease. So, we mentioned before there's a central nervous system phase that can occur in some individuals. And the neuroinvasive disease with a West Nile virus infection only occurs in very few individuals. It occurs in about 1 in 150 to 250 people that are infected. So, it's less than 1% or even less than 0.5%. But when we do see neuroinvasive West Nile disease, we can see encephalitis or meningoencephalitis. So, encephalitis is itis, inflammation, encephal, brain, so inflammation of the brain. Meningoencephalitis is inflammation of the brain and the meninges, the layers that cover the brain. So, what we see with encephalitis is we can see fever, headache, and altered mental status or confusion. So, a patient can be very feverish and very confused or have an altered mental status. And in meningoencephalitis, we can see the same thing as encephalitis, but also signs of meningeal irritation or meninges. So, we can see signs like neck stiffness and Brudzinski's sign and other signs of meningitis or meningeal irritation. So, please look up some of those signs if you want to learn more about those. And with neuroinvasive West Nile disease, we can also see acute flaccid paralysis. So, an abrupt onset of weakness and paralysis can occur with some of these patients. And we generally see the encephalitis, the meningoencephalitis, and acute flaccid paralysis that occurs more frequently in older patients. Older patients seem to be more at risk for getting these conditions. So, when I say older patients, generally greater than the age of 60. So, here is a more in-depth look at risk factors for the neuroinvasive disease of West Nile virus infections. So, number one, as we mentioned before, increasing age, generally over the age of 60. Number two, hematological malignancies, so leukemia's, can lead to increased risk of having neuroinvasive West Nile disease. Infection from an oral transplant. So, we talked about that horizontal transmission as being a possible way that one person can infect another person. It's very rare, but it can happen, and when it does happen, it can be a higher risk of that patient having neuroinvasive disease. And number four is genetics. So, some people are just more at risk for getting the neuroinvasive West Nile disease for whatever reason, there are certain genes that are in play that actually lead to an increased risk. And when a patient does have the neuroinvasive West Nile disease, this is when the fatality rate increases dramatically, and this is about an approximately 10% fatality rate. If a patient recovers from the West Nile virus, and even recovers from a neuroinvasive West Nile disease, they can have post-infectious symptoms. So, what that means is they've cleared up all of their symptoms prior, but they can have issues later. And we can generally see these symptoms in patients who had the neuroinvasive West Nile disease. So, they can have persistent memory issues, persistent fatigue, recurrent headaches, and even issues with their balance that can last for a long time. So, how do we diagnose a West Nile virus infection and how do we treat it? So, diagnosis of the West Nile virus infection is usually done through serology. So, we're looking for antibodies. So, we want to look for a West Nile IgM antibody. An important note is that there is cross-reactivity from an IgM to the Japanese encephalitis virus. So, there is some cross-reactivity to both of these viruses or the the antibody to both of these viruses.
[10:55]So, if that's an issue, PCR for viral genetics can be done, especially if it's very, very early on in the infection, if the person hasn't been able to develop the antibodies to the virus.
[11:11]They can use PCR to detect the viral genetics. So, once we make the diagnosis, how do we treat it? Treatment is supportive. This is a viral infection. There are no specific treatments for the West Nile virus. So, a lot of times we just treat them symptomatically. So, we treat their symptoms and we support them through the recovery. And they will recover spontaneously the majority of the time. But what's better is to try to prevent being infected with it in the first place. Unfortunately, there's no vaccine available against the West Nile virus. But what we can do is what I like to call mosquito hygiene. And what is mosquito hygiene? So, mosquito hygiene essentially trying to prevent being bitten by mosquitoes. So, what we can do is we can try to wear long sleeve clothes, try to cover as much skin as possible. We can also use insect repellent to avoid or repel mosquitoes from actually biting you. And we can use in certain areas, mosquito nets. So, mosquito nets can be used when we're sleeping outside to avoid being bitten by mosquitoes at night. So, those are a few different ways we can try to prevent being bitten by mosquitoes. And this is not 100% guaranteed that you're not going to become infected, but it can help reduce the risk of becoming infected. So, the references that I used for this lesson are in the video description below. So, please check out those references if you want to learn more information about the West Nile virus. And if you want to learn more about other infectious diseases, please check out my infectious disease playlist. I have many topics in that playlist. And if you haven't already, please consider liking, subscribing, and clicking the notification bell to help support the channel and stay up to date on future lessons. Thank you so much for watching, and continue to live, laugh, and learn.
