Protein Angst

Saturday, February 19, 2005

HIV 2: Viral Boogaloo

I'd like to address a few comments on the previous entry. I'll do my best to get to some of the other questions when I have time.

Steph says:

I'm more amused by the people who think HIV can be spread by mosquitos.

If it was easily spread by mosquitos, we'd all have it. All of us.

Sigh. Ignorance.

While some of the links dispelled this myth, I didn't address it specifically in my post because I thought the notion was ridiculous. As Steph notes, if it were easily transmitted by mosquitos, we'd be seeing outbreaks similar to that of the West Nile virus. Mosquitoes pick up the virus from an infected bird. The virus can survive inside the mosquito, and then when it bites a human, it can transmit the virus through the saliva it injects during the bloodsucking.

If you read my previous post, you can see why HIV is not like the West Nile virus. The H in HIV stands for Human. Not hmosquito. It can only survive and replicate in humans. There's also a simian immunodeficiency virus for monkeys. There is a feline immunodeficiency virus for cats. It only affects cats. You can have sex with your cat all you want, and you'll be safe from infection. But not from the fires of hell, you sick, sick man.

In addition, note what the mosquito injects: saliva. HIV does not hang out in the saliva.

What people need to understand is that viruses are just as diverse as human beings. Each one behaves differently, and just because one can be spread one way doesn't mean another can be spread that same way. We try to teach our children not be prejudiced against other people, but I think viruses deserve the same respect. Come on. Don't judge a virus by its capsid.

Actually, you might want to judge a virus by its capsid, nevermind. But don't judge a virus by its...being a virus.

Stephanie says:

Definitely some information that needs to get out there...have you heard that some of the abstinence-only sex ed courses teach that you can (apparently easily) get AIDS from tears?

This kind of thing makes me want to cry. And then look at my tears that would not have HIV in them were I infected.

Steph (aka Nonian) asks:

Since this is sort of related to your post, here's my most recent HIV question. I heard recently (maybe from CNN?) that we are very close to eliminating infant HIV in the US. I had the impression from the article that most of this is from early testing and administering drugs (not sure if the drugs go to the mom or baby) that prevent the passing of the HIV prior to and during birth. I have no idea how this would work, but I can sort of see how it might be possible.

However, the piece when on to say that there are also drugs that you can give to the infant once they have HIV in their system that will prevent the infant from getting (or maybe keeping?) HIV. Is this possible? If it is, why can't you do the same for an adult?

An HIV-infected mother has about a one in four chance of passing on the virus to her child. This is called vertical transmission, as if you were looking at a family tree, the virus would be traveling vertically, from one generation to the next. Sexual intercourse is, appropriately, a form of horizontal transmission, for similar reasons.

The virus may be passed on during the gestation period, since there is blood traveling from the mother to the baby, but there is a much higher risk during delivery due to the ruptures of various membranes. Anyone who's seen a baby being delivered knows there's a lot of blood involved. For this reason, cesarean section is quite effective in and of itself at reducing HIV transmission.

In recent years, what has also helped is a drug regimen. We have several anti-retroviral drugs available now in addition to the headline-making AZT. These drugs block the protein HIV needs to replicate. Note that the previous sentence did not involve the virus dying.

The pregnant woman is given anti-retroviral therapy (ART) after the first trimester until the baby is born. This reduces the viral load. If there's less of the virus floating around, there's less chance of any getting into the baby. Plus, since the drug gets passed into the baby as well, any virus that does make it into the child won't be able to replicate and infect.

After birth, the newborn gets ART for six weeks to prevent the virus from getting its figurative claws into its immune system. Unfortunately, the mother shouldn't breastfeed, since there's chance of more virus transmission.

The reason, I think, we're so excited about this is because A) everyone loves babies and B) it's easy. There is exactly one way a baby is going to get HIV, and it's from the mother. Identify the source of the virus and stop it. Simple.

Why, then, can't we do the same for an adult? Well, theoretically, we can, I suppose, if you want to pay the thousand dollars for AZT in exchange for a night of unprotected sex. And that wouldn't really work the same as a morning after pill because remember, the infected person would not have had their viral load decreased.

It's difficult to get these kinds of studies done, as you may imagine. To test the effectiveness of ART as a preventative measure, you have to get healthy test subjects to engage in unprotected sexual intercourse with HIV-infected subjects. And then give the subjects ART and see how many of them breathe sighs of relief and how many of them become infected in the name of science.

They're doing studies in Brazil, and the data look okay, but not phenomenal. No one seems to be convinced that post-sexual-exposure chemoprophylaxis (PEP)—whoa, whoa, let's break that down. post = after, sexual exposure = sexual exposure, chemo = chemical, prophylaxis = protection (remember that the fancy name for condom is prophylactic). so all those syllables mean, "chemical protection after exposure to the virus through sexual contact"—is truly effective, but that doesn't mean people won't try it. This could potentially be very bad, because it may encourage more unsafe sex and lead to even more infection.

And even after all this, there is the one word that strikes fear into the hearts of virologists everywhere: resistance. There are already AZT-resistant strains of HIV floating around.

We don't have a cure, folks. These drugs are the best we have. Let's make sure we have to use them as infrequently as possible.

Tuesday, February 08, 2005

You Can't Get AIDS from a Sneeze

My latest article is about aromatase inhibitors, a new class of breast cancer drugs, but a far more interesting article in today's science page is on Bexxar, a lymphoma drug that actually uses antibodies to administer radiation specifically to cancer cells.

A couple days ago, I read about someone whose health teacher didn't hang around with gay people because she was afraid she might catch AIDS. I didn't know what to say. I couldn't believe there were people so ignorant, yet it didn't surprise me. I will counter this ignorance by spreading knowledge, and I expect you to spread it yourself. Go on. Be a virus.

Diseases are spread by pathogens. These are any number of microscopic buggers: bacteria, viruses, fungi, etc. AIDS is caused by HIV, which is Human Immunodeficiency Virus.

Now, there is some controversy as to whether a virus can truly be considered alive, but for my purposes, I will consider it to be a living organism. It contains genetic information and the ability to pass it on. That's good enough for me. Also, it allows me to anthropomorphize it more easily.

Each virus is different. They like different parts of the body. They require different things to survive. From what I've learned, I'm not even certain we know why certain viruses behave the way they do, but we know they do, and that's what's important.

HIV is found in high concentrations in the blood, semen, vaginal fluid, and breast milk. These are the only bodily fluids you really need concern yourself with when worrying about "catching AIDS." It is present in very low quantities (if at all) in the saliva, sweat, tears, feces, and urine, but the concentration is so low as to be negligible (we're talking ten thousand times lower than in the blood). A person with AIDS — let's call him Bill — could pee directly into your mouth and you'd be safe. But that's really gross.

The other thing about HIV is that unlike the cold and flu viruses, it can't survive outside the body for very long at all. It's incredibly weak, and very codependent. HIV is hardly present in mucus in the first place, so a cough or sneeze spells a very lonely death for the virus. By the time it reaches you and scrambles around looking for a way to get in your nice warm body, it's too late.

That is the other consideration: the virus needs a way to get into your bloodstream. If Bill touches you, there is no way HIV from inside him could have gotten into your blood. You are safe. First of all, there was very little virus hanging out on his hand anyway. Plus, HIV is incredibly lazy, and it needs easy access. None of this epidermis business.

If Bill — no, let's switch gears and talk about his friend Karen — If Karen bleeds on you, you are also safe. Wash it off immediately, but don't flail around screaming, "I've got AIDS! I've got AIDS!" Like the process required to become a vampire, the blood needs to mix with your own. This is why blood transfusions sometimes led to HIV infection — now that we have HIV tests, it's less of an issue. In the same vein — no pun intended — sharing needles is another method of transferring the virus from infected blood to fresh blood.

The fact that HIV is so concentrated in the semen and vaginal fluid is why it is a sexually transmitted disease. During sex, the vaginal lining can be sloughed off, providing a route to the bloodstream. The reason gay men have a high rate of affliction is because the rectal lining is even thinner than the vaginal lining. You have the two conditions necessary for infection: a large supply of virus and a way to get in.

Every virus is different, and these are the quirks of HIV. It takes quite a bit of work to get, as direct access to the bloodstream is not very common. Plus, only certain bodily fluids carry a high risk of infection.

And of course, even after all that, you don't contract the disease immediately. The virus can party in your body for years before getting to work. All that time, though, you're able to pass it on.

The A in AIDS stands for Acquired. You cannot just magically get HIV; you must acquire it from someone else. You can have unprotected sex with three thousand people, and if none of them have the virus, your chance of having the virus is zero. Unless you already had it, in which case you have a lot of phone calls to make.

AIDS is a sexually transmitted disease. It is transmitted through sex. It is transmitted through direct blood-blood contact. You can't get it from a sneeze. Or a cough. Or a touch. And for God's sake, you can't get it from being around someone with AIDS.

If you know someone with AIDS, here are some things you probably shouldn't do with them:
  • have unprotected sex
  • take a blood oath
  • share needles
  • remove some of their blood with a syringe and inject it into yourself
If you know someone with AIDS, here are some things you should do with them:
  • give them a hug
  • shake their hand
  • kiss them
  • share your drink
It is literally safer to be around someone with AIDS than it is to be around someone with a cold. If the person with AIDS has a cold, though, watch out! You might get sick!

With a cold. Not AIDS.

Here are some informative pages on HIV transmission:
Honestly, if you meet someone who doesn't understand how HIV is transmitted and why, please set them straight.

Tuesday, February 01, 2005

Epidemics Can Induce Genetic Change

Scientist finds surprising links between arthritis and tuberculosis.

Included in this article is a bonus: the definition of "drug target." Because while you know the word "drug" and the word "target," putting them together causes them to lose all meaning. Lost in the editing room was the definition of another term with similar properties: "animal model." An animal model is a laboratory animal that has been given a disease of interest. By studying the disease — and the effects of drugs on it — in the animal, scientists can better understand the disease in humans.

alliterator asks:

"Here's my question: have you heard of the prion protein which causes the disease kuru and CJD (also known as Mad Cow Disease) and its relevance to the fact that perhistoric human civilization had widespread cannibalism?"

I have heard of prions, but I had never heard it related to prehistoric cannibalism. That's very interesting.

The funny thing about prions is they're infectious proteins. Normally, when you think of infection, you think of bacteria and viruses. Bacteria and viruses have nucleic acid, genetic material with which they can replicate and infect new cells. But a protein has no nucleic acids: it's made up of amino acids. It has no ability to replicate.

Instead, these rogue proteins seem to travel from cell to cell converting normal proteins into prions (not any protein, only the prion protein PrPC). And just like a viral infection, eventually the excess of prions causes the cell to die and release the infectious material into the open, where the disease can spread.

The initial prion is very much like a cult leader, travelling from city to city brainwashing new recruits. The recruits in turn spread the message.

I would like to look up more about prions and their relation to cannibalism, but until then, here are some useful sources for background information:

  • All About Prions
  • Prion Diseases
  • Prions: Puzzling Infectious Proteins
  • Do Prions Exist?