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  • Human papilloma virus, or HPV, has a strange reputation.

  • You might know of it as a sexually transmitted infection that causes uncomfortable warts,

  • the papilloma, but you also may have heard that it can lead to a deadly form of cancer.

  • Both are actually true, as is the possibility that you can have HPV and experience no symptoms whatsoever.

  • HPV isn't just one virus.

  • There are actually over 200 strains, and the different types of HPV can result in different

  • outcomes (which we'll get into a little bit later).

  • But first, before HPV can do anything, it has to find a way into your skin.

  • Hi, I'm Dr. Moscicki from the University of California Los Angeles, Department of Pediatrics.

  • I'm chief of adolescent and young adult medicine, and I have been studying HPV for over 30 years now.

  • So when you're looking at skin, you have several layers, and you have the very basal cell layer,

  • that is, the layer that sits right on top of the basement membrane, and right under

  • that is what we call the dermis.

  • and on top of that, you have the spinous, and eventually, you get the very top cornified cell layers.

  • HPV first attaches itself to the basement membrane, by entering the body through a wound or micro-abrasion.

  • It usually does this through sexual intercourse, but there are other types of HPV that cause

  • hand and foot warts that aren't sexually transmitted.

  • Reaching the basement layer is key because there is a receptor there that it must attach to first.

  • It's referred to as a heparan sulfate receptor.

  • This receptor actually changes the virus so that it can then attach to the basal cells.

  • Once it does this, it injects its DNA into the cell's nucleus.

  • As the basal cells matures, the infected cell makes its way to the very top.

  • ...it kind of hijacks the cell.

  • And what it does is it makes it start proliferating a lot so that it can replicate itself.

  • This all happens without your body mounting a real defense against the disease, because

  • HPV avoids expressing genes that would initiate an immune response until later in its lifecycle.

  • it looks like it's a mechanism that HPV has developed in order for its own survival.

  • But, while HPV has found a clever way to avoid the immune system, the body can still get rid of the infection.

  • Like, you know, when you're taking a shower, that top layer of skin kind of comes off.

  • ...once it gets sloughed off, if there's no other place to invade, then that infection's

  • just gonna burn out very quickly.

  • That it was a one-time chance that it found access to the basement membrane.

  • In fact, even though 80% of people in the United States are thought to contract HPV,

  • 90% of infections are cleared on their own.

  • So, if the infection doesn't usually last, whats t'he big deal?

  • Well, that's where those different types of HPV become really important, specifically

  • the ones that can cause cancer.

  • There's only about 13 types that we have associated with cancer, and they all fall into the alpha types.

  • The most famous ones are type 16 and 18.

  • They're actually responsible for around 70% of cervical cancers.

  • Types 16 and 18  are totally different from the types of HPV that cause warts, which aren't

  • pleasant but fortunately do not typically become cancerous.

  • What we believe, the way it causes cancer, is that it infects, probably, a stem cell within the basal cell layer.

  • Therefore, those stem cells, as it maturates, what happens is, literally, HPV hijacks the

  • host cell machinery, says, I want you to replicate, because every time you don't stop me, I can

  • make more and more of my DNA.

  • While replicating in stem cells, these oncovirus types of HPV will express the genes called E6 and E7.

  • These oncoproteins stop the body from killing and clearing out cells with damaged DNA, allowing

  • the cancerous cells to continue replicating.

  • So when there's a damaged cell, it's a race.

  • Their immune system is probably trying its best, but it's really pushing the system,

  • that it's replicating way faster than the immune system can even access it.

  • Fortunately, we have ways to prevent HPV from getting to this point.

  • First, there are screenings for cervical cancer that can catch the disease when it is still pre-cancerous.

  • But there is an unfortunate lack of screening methods for the other cancers caused by HPV.

  • For people who are young enough and have not been exposed to HPV, there is also a very

  • effective vaccine has been available since 2006.

  • And while some people might think it's only given to girls because of the risk of cervical cancer,

  • It's recommended for boys as well.

  • So the prevention here, we're talking about anal cancer, penile cancers, and oropharyngeal cancers.

  • So it's equally as important for boys to get this vaccine as it is for girls.

Human papilloma virus, or HPV, has a strange reputation.

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    Jerry Liu posted on 2019/07/10
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