Influenza Introduction PM250

hello everyone dr alad roberts here so this will be the first time that i'll be teaching most of you so i hope the slides are easy to understand the audio is of good quality the information on the canvas pages is clear and easy to engage with and to make things a little bit easier i've split this lecture up into four different videos to make it easy to digest and easy to learn come the exams so with all that being said if you do have any problems with the content or the lecture materials i am just an email away so please do get in contact with me and i will try to help out where i can so now that the formalities are out of the way let's crack on with the videos so this is a standalone lecture on pm 250 where we are going to look at the influenza virus as a prime example of an infectious disease of the respiratory system now this is the only virus that we are going to look at in this module and whilst there are many other viruses and indeed respiratory viruses to choose from we are going to look at influenza as one of the most widely known viruses that is if we forget about severe acute respiratory syndrome coronavirus 2 for a minute if that's possible and we're not only going to look at it because everyone knows about it but because of its burden to the healthcare system it's genetic traits that lead to both seasonal epidemics and global pandemics as well as its biochemistry which results in various symptoms and syndromes so with all of that being said what do i hope you'll know and understand by the end of this video series well i would like you to understand the basics of the influenza virus from its classification to the different types of influenza virus as well as the syndromes and symptoms associated with infection i would like you to review some data from public health whales to see what effect influenza has on the health service in wales particularly between different years i would like you to be able to explain the structure of the influenza virus noting all of the core components as well as how these components are encoded by the viral genome you should be able to describe the replication process from how the influenza virus attaches to host cells becomes internalized and hijacks the host cell machinery in order to produce new virus particles and finally i would like you to understand what antigenic shift and drift are but more importantly how these processes lead to both minor and major changes in the structure of the influenza virus and its genome now because we only have a single lecture slot on viruses you may have to draw upon some of your year 1 virus knowledge however where possible i have tried to explain things as simply as possible now as a quick recap one of the key things we need to remember about viruses is that they are what we would call metabolically inert obligate intracellular parasites this essentially means they are fundamentally unable to function or replicate without the use of a susceptible host cell and because of the parasitic nature of this interaction the host cell is exploited usually to the point of death so that the virus can generate new virus particles and infect new cells now what this means in a very basic way is that viruses are non-living unlike bacteria fungi and conventional parasites which all have the ability to extract nutrients from the surroundings allowing them to grow and replicate independently viruses on the other hand need to use the machinery of a host cell to replicate hence the term obligate in their description now as i said at the start this video series is solely focused on the flu which is or at least was one of the most well-known contagious respiratory illnesses known to us now obviously covid19 has since changed this but that doesn't detract away from its importance and a need to learn about this disease so the term flu is short for influenza which actually refers to the illness with the causative agent being the influenza virus and typically speaking the influenza virus infects the upper respiratory tract and in severe cases the lower respiratory tract leading to various levels of severity from a short-lived mild illness to severe and potentially fatal illnesses so if we have a close look at the respiratory tract we can see the various anatomical sites on the right now as i said on the previous slide both upper and lower sections can become infected with the influenza virus leading to multiple different syndromes so when the mucous membrane of the nasal cavity becomes infected rhinitis occurs now something important to note here is that rhinitis is a syndrome caused by influenza not an influenza infection and the reason why i'm pointing this out is that you can get bacterial rhinitis and even allergic rhinitis essentially it only relates to the inflammation of the mucous membrane in the nose with no bearing on what is causing the inflammation now there are two other upper respiratory tract syndromes associated with influenza infection and they are pharyngitis which is the inflammation of the pharynx which is at the very back of your mouth and laryngitis which is the inflammation of the larynx which is essentially the area surrounding your vocal cords now going deeper into the lung we end up with lower respiratory tract syndromes which include tracheitis this is the inflammation of the trachea and usually only occurs when an infection in the upper respiratory tract isn't cleared and migrates down into the lung next we have bronchitis bronchiolitis and pneumonia which is the inflammation of the bronchus bronchioles and alveoli of the lung and because of their location deep within the lung inflammation as a result of infection be that through influenza or other infective agents it's extremely difficult to treat now these words on the left are syndromes associated with infection however the infection causes the syndrome and then the syndrome results in the symptoms which in the case of influenza includes things like fever or a sense of uncontrollable shaking despite having a high temperature so it's not as if you're cold a non-productive cough a runny nose specifically as a result of rhinitis headaches muscle aches or just a general feeling of fatigue now most of these symptoms are not unique to the flu or an infection caused by influenza but they are almost all commonly associated with the flu and it's the reason why we use the term flu-like symptoms for many other respiratory infections now there are some additional symptoms associated with influenza infection such as vomiting and diarrhea which are possible however this is more specific in younger children and is rarely observed in infected adults now like many respiratory infections the influenza virus is thought to be primarily transmitted in aerosolized water droplets from one person to another when they sneeze cough or even talk other potential routes of transmission include fomite transmission which is where contaminated droplets land on a surface and an unsuspecting person puts their hand in the contaminated droplets before going on to touch their eyes nose or mouth and what this results in is an estimated three to five million cases of severe influenza worldwide each year and we class severe cases as those requiring medical intervention now the number for less severe cases can be much more difficult to predict because there is an abundance of under-reporting as people recover without notifying various health agencies around the world now of the people suffering with severe infections there will be anywhere between 290 and 650 000 deaths depending on the year in question but i guess a key question is who is most at risk of these severe infections and therefore who has an increased chance of death from the influenza virus now before we go into this it's important to remember that anyone and everyone is capable of getting the flu and there is always the potential for it to transpire into a severe infection but some people have an inherent increased risk so a few examples we have children less than five years old whose immune system isn't as well developed yet adults over 65 years old whose immune system might be deteriorating pregnant women due to changes in their body anyone with an underlying chronic condition such as people who have cardiac pulmonary renal or liver problems and even those with diabetes we have those with a suppressed immune system so people who are undergoing cancer treatment or who have conditions such as hiv and aids all of these are at an increased risk of getting normally any infection but in this instance of getting the flu now the last at-risk group are healthcare workers and that has nothing to do with their ability to fend off the disease as is the case in our other groups it all boils down to their exposure rate which is increased by the very nature of their job and we can see this during the current covert 19 pandemic where a lot of healthcare workers are becoming infected with covert 19 because of the working conditions and the people they are coming into contact with now typically speaking to help these at-risk groups they are given priority access when it comes to flu vaccinations to help protect them and we'll talk more about this later on now i guess the next thing we need to look at is what happens when someone becomes exposed to influenza what is the clinical manifestation of a typical influenza infection well typically from the point at which a person becomes exposed to the influenza virus to the point of displaying symptoms it's known as the incubation period and is essentially the time it takes for symptoms to become apparent which can be anywhere between one and four days now the reason why this is so variable is based on the initial exposure for example if you were to breathe in an infected water droplet containing 1 000 virus particles it might take four days for symptoms to develop whereas if the water droplet contained 10 000 virus particles it might only take a day for symptoms to develop now when these symptoms do develop typically you'll be feeling fine going about your normal business feeling fine having a meal feeling fine going to sleep feeling fine and bam when you wake up the symptoms hit you like a ton of bricks we call this an abrupt or sudden onset of symptoms and is very common for influenza infections now typically speaking an acute illness from influenza infections will last between five and seven days at which point some symptoms will start to reduce so things like the fever headaches muscle aches etc however it can be many weeks before a full recovery is achieved now if a chronic infection takes hold so if the influenza virus gets deep into the lung and causes pneumonia which isn't that uncommon well it can take a lot longer to clear even with medical interventions you are looking at more than seven days recovery but the sad truth is that even with medical intervention some patients in the region of 10 to 20 with chronic influenza induced pneumonia they do not recover from the infection now those percentages are quite high however the number of people getting the chronic form is relatively low so it's a high percentage of a small population now taking a step back for a second people are typically infectious with the influenza virus for a period of around three to five days after the onset of symptoms however children are known to be infectious for a period of around 10 days after the onset of symptoms and some adults who are immunocompromised still shared influenza virus particles for weeks after the onset of symptoms and as i said before the level of contagiousness depends on the concentration at which the influenza virus is being shed so that basically wraps up the clinical manifestation of the influenza virus there's just one more clinical side of things we should look at and that is essentially the burden of influenza on the welsh healthcare system so here are some infographics about influenza in wales for the 2019-2020 season ending mid-march just before the covid19 pandemic now what i would like you to do is go through these statistics and see how influenza affects whales and to help save your eyes i have linked two documents on canvas which detail the effects of the influenza virus during the 2018-2019 season and the 2019 to 2020 season and i don't want you to go through all of the data as these documents are 60 odd pages in length what i would like you to do is just look at the infographics in these documents maybe a few graphs and see the effects of influenza on the welsh healthcare system and how it potentially changes per season and per year and with that we come to the end of the video it's been a gentle introduction into the influenza virus in the next video we're going to ramp things up a notch and take an in-depth look at the influenza virus focusing on its structure and its genome you