If this is your reaction to seeing a mosquito at Charlie Sheen’s house, then you are unforgivably stupid.
For anybody who hasn’t heard, Charlie Sheen, the former star of Two and a Half Men who made “Winning” 2011’s most annoying catchphrase, recently announced that he is HIV-positive. HIV stands for Human Immunodeficiency Virus, and despite denialist claims to the contrary, it is the virus that eventually causes AIDS (Acquired Immune Deficiency Syndrome). A person with AIDS has a severely depressed immune system. As a result, he or she might succumb to diseases that healthy people don’t normally contract, or which they are able to fight off if they do.
In the early 1980s, when HIV was first discovered in the United States, a newly-infected person might have a decade left if he was lucky. Now, HIV isn’t necessarily the death sentence that it once was. With treatment to suppress the growth of the virus and to quell opportunistic infections, a person infected with HIV today might reasonably expect to live long enough to die of other, non-HIV-related causes.
Still, HIV is a life-changing – if not life-ending – diagnosis, so it might be helpful to learn how HIV is transmitted, and to decide whether we really need to bathe in Off! mosquito repellent before visiting the Sheen residence. Have a seat, kids: it’s time for the After-School HIV Special.
Generally, HIV is transmitted in bodily fluids, so the quickest way to become HIV-positive is to swap liquids with somebody else who is HIV-positive. The most common routes of HIV transmission are through sexual contact and the sharing of injection drug paraphernalia. An HIV-positive mother-to-be can also pass the virus to the developing fetus in her womb, or she can transmit the virus via breastfeeding.
Health care workers also assume a small risk of HIV infection due to the danger of being accidentally stuck with needles used on HIV-positive patients. There is an even smaller risk to blood and organ transplant recipients, but advanced screening techniques have done much to minimize this threat.
And what about mosquitoes? Surely those damned winged bloodsuckers up the HIV risk factor by a thousand, what with their indiscriminately poking their probosces into one unwitting donor after another, right?
Well, no. Not that a mosquito particularly cares about spreading disease, but she is prevented from spreading HIV by several factors. First, the construction of a mosquito’s blood-straw does not allow previously-sucked blood to flow downward into her most recent host. A mosquito’s mouth parts have two tubes: one carries saliva downward and the other draws blood upward. The saliva contains chemicals that prevent your blood from clotting, but it does not contain HIV from previously bitten humans. And why not?
Because HIV is digested in the mosquito’s gut. In a human host, HIV binds to T cells and begins replicating, but mosquitoes don’t have T cells. The virus has nothing to attach to in the mosquito’s gut, so it simply gets broken down by the insect’s vile brew of digestive enzymes. HIV never migrates from the mosquito’s belly to its salivary glands.
So, the virus cannot follow the gut-to-salivary-gland route that some other pathogens – notably malaria – follow. But what about a more direct route of infection? Mosquitoes are sloppy eaters, and they rarely use napkins. When a mosquito leaves her host, she’s likely to have a bit of blood clinging to the end of her schnoz, and if that blood were HIV-positive, couldn’t she inject it into her next host, especially if she decided to feed again within a very short period of time?
Sure, that’s possible…in the same way that it’s possible to win the lottery twice and be struck by lightning five times within the same ten-minute period, and to reach the hospital just in time to see your wife giving birth to octuplets, just before she announces that she’s leaving you for Charlie Sheen. Which is to say, it isn’t very possible at all.
Surprisingly, the virus count in an HIV-positive person’s blood is pretty low. It’s highly unlikely that the blood stuck on the end of a messy mosquito’s maw contains even a single virus, let alone a large enough virus load to start a new infection in the mosquito’s next host. Natalie Peretsman, writing for scienceline.org, reckons that if a mosquito were to drink from an HIV-positive person whose blood virus level was 1000 per milliliter, and if that mosquito were to immediately feast on a nearby healthy person, there’s still only a 1 in 10 million chance that the mosquito would transmit even a single virus to the healthy person’s blood.
So what have we learned? Mosquitoes transmit many dangerous diseases, but HIV thankfully isn’t one of them. You needn’t fear a mosquito at Charlie Sheen’s house, unless it turns out that Charlie Sheen has also contracted malaria, dengue fever, or chikungunya.
On a personal note, the vectors of HIV have been known for decades, and it’s well established that mosquitoes are not among them. To make a joke like this either (A) portrays devastating ignorance of (and indifference towards) a very real public health issue, or (B) says that you’re the kind of person who thinks it’s hilarious to paint yourself and your supporters as blithering idiots. In either case, shame on the person who made this macro, and shame on anybody who shares it. Abysmal ignorance isn’t funny. Stop glorifying it.