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Current time:0:00Total duration:11:32

Video transcript

what is HIV and what is AIDS well let's first look at HIV HIV is a virus that attacks our immune system and if we expand this out we can see that that's reflected in its name human immunodeficiency virus so this implies that it does something to our immune system somehow and we'll actually explore that a little bit later on and if we don't treat HIV it'll eventually cause AIDS in the infected person acquired immune deficiency syndrome so right away you already get a sense that HIV attacks your immune system so destructively that you end up acquiring an immune deficiency syndrome it puts you into a state of immune system failure so you end up not being able to fight off even the most basic infections and this immune 'less state is what we call AIDS so let's explore this a little bit further now let's actually use the help of a graph this might be helpful so here's our graph and we'll put time down here on our x-axis and actually just to make this extra useful will put weeks in this beginning part here and then we'll transition to years here and you'll see how this is relevant in a few moments here so on the y-axis here we'll put cd4 T lymphocyte count T lymphocytes are a really really important type of immune system cell and cd4 just refers to a type of protein that's stuck through their cell membranes that's that's kind of how we like to identify them by this protein on their membranes and the reason they get a special spot on an entire axis of our graph here is because they're super important in the progression from HIV infection to AIDS because as you might have suspected it turns out that HIV preferentially loves to infect these cd4 cells of our immune system and why is this so bad well these cd4 cells also called helper t-cells play a huge role in signaling your other immune cells to come and destroy any given infectious particle that our body discovers like maybe strep throat bacteria or flu viruses or even HIV viruses for that matter so the cd4 cells are kind of central they're almost like little amplifiers of our immune system so because HIV loves to infect and kill these cells it completely disrupts how our immune systems function and renders it essentially useless so let's say you acquire HIV in your body either in your bloodstream or your your tissues maybe through unprotected sex with an infected partner that would be the most common method of becoming infected with HIV and adults at least what happens well the main thing is that the virus really quickly gets into your white blood cells so these T helper cells the cd4 cells we talked about but also some other white blood cells like your macrophages and so on and from inside a white blood cell it can do two things one it can sort of hijack your cells machinery so it manages to insert its genetic material into your own cells DNA and from there it starts to make lots and lots and lots of copies of itself lots of new HIV particles actually that's that's really really important so let's put that on our graph to let's say viral load here on another y-axis here viral load referring to the amount of HIV in your bloodstream so we can see that after our primary infection here the viral load starts to increase it's hijacked our T helper cells and now new HIV particles are being turned out and our viral load is majorly on the upswing and you'll notice that the viral load is starting to rise that around the two to three week mark and that's just because it takes a bit of time for the HIV virus production to start ramping up within our bodies and of course a major concern here is well the more HIV there is in your bloodstream the more cd4 cells get infected get hijacked right but the biggest problem here I think number two here is that HIV infection of your cd4 cells triggers a self-destruct sequence within these cells so you end up losing these cd4 cells and even worse the self-destruct sequence doesn't just destroy the infected cells it even destroys nearby immune cells that maybe have come into the area to try to help out so I won't go into the mechanism in this video but you do end up losing lots more immune cells than just the infected ones and that's part of why you see this massive drop-off here this line representing our our cd4 t-cell numbers as is really steep downward slope we're losing lots of t-cells while at the same time our HIV viral load is going up and causing more and more infection of ourselves the other thing I want to point out here is you can see this massive rise in viral load in this pretty massive drop in cd4 levels and this huge viral load means that this time period right early on in an infection is when someone with HIV has the highest risk of transmitting it to someone else I guess one good thing here is that eventually maybe a month or so in your your immune system gets somewhat of a handle on the virus and it starts to make anti HIV antibodies right those are just antibodies against HIV so they start to fight off the virus to some extent and this is called seroconversion when you make antibodies to something so now we've cero converted to HIV so now the antibodies get to work on on helping to destroy the viral particles and that's why we see this decrease here in viral load in the bloodstream because our immune system is starting to control the viral levels to some degree and this also gives our cd4 cells a chance to recover to some extent because there's less virus around to infect them so you might be wondering how you're going to feel during all this with this massive battle going on inside your body well you're going to feel sick you're probably going to feel like you're having the worst flu you've ever had so about here about a month or so in at cero conversion you start to fight the infection and as a result most people get some serious flu-like symptoms so things like headache and and fever and sore throat muscle pains joint pains some people get swollen glands just sort of fatigue and feeling unwell some people get a rash some people get some open sores in their mouth these are some of the more common symptoms of an acute infection with HIV and this flu-like illness that people experience is referred to as acute HIV syndrome and the reason for a lot of these symptoms is because well when immune system cells get really active or when they die off both of which are happening here of course they tend to release these little chemical signals that cause inflammation sort of all throughout your body and so this is what underlies a lot of these symptoms here so back to our graph the immune system can't completely kill off the HIV even though we have antibodies now right and and that's because a remember the rate of immune system killing is roughly matching up with the rate of new viral particles being produced and B because the virus has sort of taken up a residence and some really really hard to reach reservoirs within our body like within the brain and within our bone marrow and within our genital tract because of these two reasons these curves tend to sort of stabilize at some point they reach a set point where again our immune system is killing off HIV at a pretty similar rate to which HIV is replicating so the curves start to come together a bit more and stabilized somewhat so this period here is thought of as the start of the second phase of HIV infection what's called the latency period or or chronic HIV this acute infection back here being phase one so in this latency period we don't tend to see any clinical signs of HIV illness the person is often asymptomatic they're still infectious but there are few or no symptoms during this phase and without treatment this phase will last on average about ten years and I said that our curves here stabilized right but it turns out that HIV is actually replicating killing our immune cells just a teensy little bit more than our cd4 czar recovering so over this long period of time Phase two eventually again without treatment HIV will start to overwhelm our immune system and we'll start to see symptoms again so things like fever or muscle pains rippling glands really similar to the acute infection and and again much for the same reasons as before and many people at this stage of the illness experience significant weight loss HIV causes you to use more enter than usual and also prevents you from absorbing nutrients from your food as well as you normally would so we often see some significant weight loss for for these and a few other reasons as well eventually if our cd4 cells get to a critically low number and results in our having no functional immune system that's what aids is essentially a state of being where we have no immune system so at this point this is when certain bugs bacteria and viruses that would never stand a chance against even a minimally effective immune system these things start to infect the person and we refer to these specific infections as aids-defining illnesses because we just know that if somebody has one of these illnesses they just cannot have a functioning immune system it just wouldn't happen or at least it would be really really unusual so there's a high suspicion of the this person having AIDS and not just an HIV infection anymore if they have any of these aids-defining illnesses two examples of aids-defining illnesses are two fungal pneumonia is one called Pneumocystis pneumonia and one called cryptococcal pneumonia these are two common aids-defining illnesses and again these aren't the types of infections that you get when your immune system works even a little bit so actually one of two criteria have to be met before we can say someone has AIDS either they have to have extremely low amounts of cd4 cells in their blood and to get a little bit technical here it's if they have less than 200 cd4 cells per microliter of blood with the normal count the normal cd4 count in this amount of blood it should be around a thousand to 1,100 cd4 cells or regardless of cd4 count if they have any of the aids-defining illnesses like either of these for example then we can say that they have developed AIDS and so you might have suspected this but it's actually the overwhelming impact and the complications of serious infections that you pick up because of the immune deficiency and AIDS that actually results in the death of the person so from HIV infection to eventually an incredibly high amount of viral particles and low amount of cd4 cells in the bloodstream to development of a completely non-functional immune system and AIDS very quickly leading to overwhelming infection by essentially every infectious pathogen from A to Z and because of this death results