Within the human papilloma viruses as a group, there is a lot of variation based on their DNA sequence. DNA is the Master Plan for the cell, and it is also the Master Plan for the virus. DNA contains the plans for cell-specific proteins, which are what make things and do things within the cell, and all cells and viruses have their own DNA.
Remember: Different strains of HPV=different DNA=different proteins.
Because of these differences in DNA sequence, some strains produce specific proteins which in true, terrible-at-naming-things Scientist fashion, have been called E6 and E7.
E6 and E7 run around the host cell and interact with some very important host cellular proteins, which, in the same scientific naming tradition, have been dubbed p53 and Rb.
p53 and Rb play vital roles in making sure that a cell does not divide when it shouldn’t. For instance, a cell could have damaged DNA. Under normal circumstances, the p53 and Rb proteins are guardians that survey the cell and assess its readiness to divide. They have the power to say, “Stop! We are not ready to divide! Halt at once, and repair our Master Plan!” and the cell will listen, repair DNA, and not divide until p53 and Rb are cool with it. E6 and E7 find p53 and Rb and physically prevent them from sounding the alarm, so suddenly, a cell that probably shouldn’t be dividing at all is instead dividing like crazy.
So we have cells dividing like crazy, creating masses that aren’t useful to us where they shouldn’t be…Sounds like cancer, right?
That’s because it is cancer! See? I knew we could Science this together!
Luckily, not all HPV viruses have E6, E7, or similar proteins. And most humans with an intact immune system will either completely fight off most HPV infections, or the immune system will beat the HPV into dormancy.
At the same time, though, it is very rare for cervical cancer cells to not be infected with HPV, which rather strongly suggests that most cases of cervical cancer can be attributed to HPV. Why wasn’t the HPV infection defeated by the immune system? That may be because the human picked up a particularly nasty strain, but there’s also the fact that some humans don’t have an intact immune system—they could have an inherited immune disorder, or diabetes, or be on systemic steroids to treat a whole bunch of things, or have AIDS…I could literally make a blog entry on reasons why folks may be immunosuppressed.
The particularly nasty, common, high-risk strains of HPV with proteins E6 and E7 are called types 16 and 18.
Due to producing proteins E6 and E7, these strains are much more likely to cause cancer.
There are also two very common HPV strains, strains 6 and 11, and they usually cause anogenital warts. However, these strains can also potentially cause cancer, and since so many people are infected by them, types 6 and 11 statistically give at least some people cancer. It’s sort of like how, even though it is extremely unlikely, people manage to get struck by lightning. There’s just a lot of lightning and a lot of people. Statistically, someone will get struck.
So that’s the HPV virus in a nutshell. We’ve Scienced the heck out of it! With that information in mind, let’s discuss the diseases caused by these cellular shenanigans!
Tell Me Why I Care: The Effects of HPV Infections
Most commonly, HPV can cause cervical cancer. These same strains can also cause anal cancer, oropharyngeal cancer, and something called respiratory papillomatosis which is a disease that occurs rarely when an HPV infection is transmitted to an infant’s respiratory tract from their mother during vaginal birth. This means that masses will grow in the infant’s airway that will suffocate them if not removed by surgery or lasers.
All of these are terrible. All of these could potentially be a blog entry all by themselves.
However, given that this is the Sheroes blog and Sheroes has a lot of cervix-having members, I’m going to give you a relatively brief, generalized overview of cervical cancer.
Luckily for women of North America and most industrialized countries, we have access to something called a pap smear.
For readers who haven’t experienced this not-especially-fun-but-also-generally-not-too-painful procedure, a pap smear is when a doctor takes a sterile, specialized brush on a stick and swabs it lightly over your cervix. The brush picks up a layer of epithelial cells, the very cells HPV infects. The doc then sends the sample to a lab.
A technician can put infected cells on a slide, stick the slide under a microscope, take a peek, and say, “Huh, this is not how a cervical cell should look!”
And then they will send the report to your doctor, who will tell you there is something called a dysplastic change.
Dysplastic change is a fancy phrase for “your cells look weird”. However, in a woman who has had proper screening at regular intervals throughout her adult life, this is probably not a cause to panic right away since the change has probably been caught early. Depending on the individual patient, doctors tend to opt for either “watchful waiting” or something called a colposcopy and biopsy, in which case they’ll coat your cervix with a very dilute acid that makes the HPV infected cells turn white. They will then take a small sample of your cervical tissue called a biopsy, and send that to the lab for analysis.
If the biopsy does show evidence of cancer, then the doctors can treat it with the usual suspects: surgery, radiation, chemo.
While a treatment plans are highly individual, in general, cancers which are caught early and confined to the surface of the cervix can be treated with a simple outpatient surgical procedure with nearly 100% success, as long as all of the cancer is cut out.
However, cervical cancer has a tendency to spread locally. It can move to the uterus, fallopian tubes, or ovaries. This development may also necessitate a hysterectomy. That can be really hard for women to go through emotionally, but again, survival rates at this stage are around 85%.
Even worse, the cancer can also invade nearby structures, like the anal canal, or ureters. One cause of death in cases like these is kidney failure, because the cancer literally blocks urine from getting out, which damages the kidneys irreparably.
In cases this advanced, patients may be offered a procedure that goes by several names, one of them being “hemicorporectomy.”
Dust off your Latin and Greek; we’re going to break this word down:
Let’s take a moment to think about that word and what it might mean for a patient.
The patient’s legs, colon, reproductive system, and lower urinary tract are removed, because the cancer has spread that far. Doctors recreate what structures they can, but they’re surgeons, not magicians. It is a radical surgery with radical consequences. It is not done lightly—it is done because the patient will die without it. Once cervical cancer reaches a certain stage, there is no radiation or chemotherapy that has been shown to increase survival rates.
And some patients still die, either because the cancer has spread too far, or because it recurs. It is a horrible disease, and while it can be screened for, screening does not help women who without access to regular screening. Since cervical cancer generally does not become symptomatic until relatively late, cases in unscreened women can be quite advanced, and the consequences can be devastating. It is estimated that over 4,000 women will die of cervical cancer in 2014.
That’s terrible. The vast majority of these cancers are due to HPV infections and, thus, can be prevented. Luckily, there are two HPV vaccines on the market: Gardasil and Cervarix. Gardasil protects against HPV strains 6, 11, 16, and 18. Cervarix only protects against strains 16 and 18.
These two vaccines are made from viral proteins produced in bacterial, yeast, or insect cells. They cannot cause HPV infections because there is no viral DNA in the vaccine. Instead, they stimulate the immune system to respond to the viral proteins, so if the recipient is ever exposed to that strain of HPV, the immune system will be ready to kill the virus and prevent an infection.
How awesome is that? Get vaccinated! Get your kids vaccinated! Vaccines for everyone, less cancer and anogenital warts and respiratory papillomatosis for all! Heck yes!
Still not convinced? In the next installment, I’ll answer common questions about the HPV vaccine.
Fancci is a US osteopathic medical school student in her clinical years. She hopes to one day open a rural family practice clinic, but first needs to survive the rest of med school and a residency.
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