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Studying for a test? Prepare with these 7 lessons on Infectious diseases.
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Defining AIDS and AIDS defining illnesses

Video transskription
- So we know that an untreated HIV infection destroys your immune system and leads to essentially an immune less state that we call AIDS, acquired immune deficiency syndrome. So how do we know when an HIV infection isn't just HIV anymore? How do we know it's progressed to AIDS? Well, in one or both of two ways. So here's a graph I'll use to explain. So here's CD4 T cell count on this y-axis. And here's a little timeline and we'll say that 10 years is about here. Because in an untreated HIV infection it takes about 10 years before your immune system is completely destroyed and AIDS is developed. So when your CD4 cell count has dropped from its normal levels, right, of about 1,200 or so CD4 cells per cubic millimeter of blood to less than or equal to about 200 cells per cubic millimeter of blood, you've developed AIDS. That's one of two ways to tell. The other possible way to know if you've developed AIDS is if you have any of what are called the AIDS defining opportunistic infections. Which are sicknesses that can only take hold in your body if you have a failing immune system. So regardless of your CD4 count, if you have any of these opportunistic infections and, of course, an HIV infection as well you will be diagnosed with AIDS. So let's do some drawing here to look at what types of AIDS defining illnesses can come on and when they might come on. Because it's important to be on the lookout for signs and symptoms of these conditions. You know because they can be really dangerous to your health. So generally speaking, people with CD4 counts greater than 500 cells per cubic millimeter of blood are not at risk for opportunistic infections. But if you're hovering right around 500ish, then sort of the daily ebb and flow in your CD4 counts means that you might develop some minor infections like thrush in your mouth. Or yeast infections in the vagina. So thrush symptoms to look out for would be white patches on the gums or on the tongue. And you might also get some pain in the mouth or in the throat and that would cause some trouble swallowing. And yeast infections symptoms might include vaginal irritation or itching and also a thick white discharge. And I should probably clarify, so all of these ranges that we're looking at, these aren't set in stone. So you could get certain opportunistic infections at slightly higher T cell counts, or CD4 cell counts, or slightly lower CD4 T cell counts. These aren't sort of fixed numbers. These are just sort of ranges. Good, so, if your CD4 levels continue to drop you could develop something called Kaposi's sarcoma which is a tumor, a set of tumors caused by human herpesvirus-8. Which can only really infect a person with a weakened immune system. So the classic signs that you should look out for with Kaposi's sarcoma are these purple patches or nodules, growths almost, that appear usually in the mouth, on the gums, or on your skin. If your CD4 count drops even further to between 100 and 200 cells per cubic millimeter of blood, then you might develop some of the more severe opportunistic infections. For example, Pneumocystis jiroveci pneumonia. Also known as Pneumocystis carinii pneumonia or PCP. So this is a fungal infection of the lungs. And it causes a really, really, severe chest infection. And in fact this is most often the cause of death for someone with AIDS. Two other common fungal infections that might take hold are Histoplasmosis and Coccidioidomycosis. It's a bit of a mouthful, Coccidioidomycosis. And these two are pretty severe because they infect many different parts of your body, not just your lungs. So, you can look out for a PCP infection because it presents kind of like a chest infection. So you'd have shortness of breath, you'd have a cough, you'd have chest pain. And, you know, at this point your immune system would still be able to mount a fever, so you'd have a fever. And these two fungal infections present in a similar way, right, Histo and Coccidioido. But remember I said that they're systemic diseases so these can also cause some weight loss and just general fatigue. Those are systemic symptoms. Now if your CD4 levels continue to fall, to between 50 to a 100 cells per cubic millimeter, you can start to develop opportunistic infections that affect your brain such as Toxoplasmosis and Cryptococcosis. So Toxoplasmosis is caused by a parasite and it can cause Encephalitis which is swelling of the brain. And because of this swelling of the brain or Encephalitis a person might develop neurological symptoms like a headache, or weakness of their muscles, or seizures. These are all signs of a sick brain. And Cryptococcosis is yet another fungal infection. And this one usually starts as an infection in your lungs. And then it sort of moves up to your brain and causes Cryptococcal meningitis which can rapidly be fatal. So symptoms of Cryptococcal meningitis would be sort of the classic meningitic symptoms, things like a headache, and neck stiffness, and a fever. And while we're in this little bracket here, two other organisms that can cause serious infections, right, between this 50 to a 100 bracket are Cryptosporidiosis and CMV, Cytomegalovirus. So Cryptosporidiosis causes severe gastrointestinal symptoms. So you'd get this chronic, longstanding, watery, diarrhea. Because your intestines just aren't absorbing food or water properly. You would get serious stomach cramps and you'd have severe weight loss. And CMV here, actually CMV is present in most adults but it only really starts to cause trouble if something's wrong with your immune system. So in someone with really low CD4 levels, CMV can cause problems in the digestive system as well. So the last one I'll talk about happens if your CD4 cell count is less than 50 cells per cubic millimeter of blood. And this one is called Mycobacterium avium complex or MAC. And this bacteria sort of similar to all the other bacteria, and viruses, and fungi that I've talked about so far. They're all present in many different places soil, water, on trees, really many places in the environment. But again, they don't cause any problems in people with healthy immune systems, we just fight them off. But MAC in a severely immunocompromised person, like someone with AIDS, can cause a really, really serious infection that spreads through the bloodstream to many other parts of the body. And that will result in things like high fevers, night sweats, diarrhea, all sorts of systemic symptoms. And MAC can be rapidly fatal as well. Now everything I've talked about, all of these AIDS defining opportunistic infections, they can be treated with the right medications. So with access to treatment they don't have to be life-threatening. You just have to get medical help right away. And then once they're treated the focus would then be on raising your CD4 cell count with ARV treatment, like HAART. So that hopefully your immune system gets stronger and none of these develop again.