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.

5 Comments:

  • med school trivia: Actually, AZT is so good at preventing HIV infection in infants that we don't even do Cesarean sections on all HIV infected mothers anymore. They do if labor lasts too long, but most HIV positive mothers deliver normally (i.e. vaginally) nowadays.
    Laura

    By Anonymous Anonymous, at 9:45 PM  

  • Cool post.

    If you would, would you describe why viruses appear in some bodily fluids, but not in others?

    By Anonymous Scott Elyard, at 1:01 AM  

  • All good things to know. And you are my science hero. I just thought you should know.

    By Blogger Syd/GP, at 12:43 PM  

  • "The H in HIV stands for Human. Not hmosquito." HAH! Awesome.

    By Anonymous elisheva, at 2:20 PM  

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