Who Are the Bloodsuckers Attracted To?
Wednesday, August 21, 2013
I am writing this from a dusty campsite in a remote corner of Yosemite National Park.
Despite dousing myself in DEET last night and donning my Don’t Judge Me I’m Camping long johns (which protected every inch of skin from mosquitoes), I’ve just located a large red welt on my left arm that is begging to be scratched. How did those little buggers get through my well-planned layers of defense?! Anyone who has seen the movie Jurassic Park knows that mosquitoes have plagued our planet for a 100 million years, and over that period they’ve become very good at ruthlessly pursuing blood meals.
As a public health physician, I get lots of questions every summer about mosquitoes and the dangers of West Nile Virus, from folks relaxing in their backyard to eager campers heading out into the wilderness. Here are the most common questions I hear: Do we have West Nile virus (WNV) in our mosquito population here in Santa Barbara? What can I do to decrease the bites I get at home? And are mosquitoes really attracted more to certain people? (Side note: Everyone is convinced that they are one of those people. Including me.)
I will attempt to answer some of those questions, and put the risk of WNV in perspective. The virus is transmitted to humans through mosquito bites and has gained infamy in recent years for some well-publicized cases where the infected person developed progressive neurological disease and eventually died. The fact that there is no treatment and no vaccine adds to public alarm when one of these cases occurs.
But the truth is, these cases are incredibly rare. Over the past five years, our county has had only one case of WNV, and it was not fatal. That means you are more likely to get bitten by a seal (it happens) than to get sick with WNV if you live in Santa Barbara County. Although we know the virus is here based on routine testing of dead birds, horses, and chickens, human disease is just not that common.
Interestingly, surveillance testing of healthy blood donors for WNV has also shown that the vast majority of people infected with WNV show no symptoms. According to the Centers for Disease Control and Prevention (CDC), only one in five people who are infected will develop symptoms, which are usually minor (fever, headache, fatigue); only about one percent of infected people will develop serious illness. Hopefully these statistics will help to relieve worry, although they won’t relieve the annoying welts you’ll get from our ever-present, ever-biting homegrown mosquito population. For that, you’ll need to take some preventive measures.
The first step in protecting yourself and your family is to mosquito-proof your home. Most mosquitoes are homegrown—they breed in standing water—so this is a problem you can do something about. Eliminate standing water in gutters, pool covers, pet water dishes, and bird baths on a regular basis. Next, make sure all open windows and doors have solid, hole-free screens in place. Mosquitoes are weak flyers, so placing a large fan on your patio can also help keep them at bay. These measures will significantly reduce the number of pests you have as guests around your home—no embarrassing long johns or smelly repellants required.
The peak hours for mosquito bites are from dusk to dawn, so covering legs and arms with protective clothing is wise. On a full moon, they are 500 times more active, according to the American Mosquito Control Association. I always get asked which repellent I recommend, and the answer is that it depends on your personal preference. Repellants containing DEET, picaridin, oil of lemon eucalyptus, and para-menthane-diol products will provide longer-lasting protection. Spraying clothing with an EPA-registered repellant creates an additional barrier. Citronella candles, despite excellent marketing, only have a very mild anti-mosquito effect.
But what if you still get bites, despite faithfully following all of the above advice? Scientists have studied more than 350 odor compounds produced by human skin and drawn some helpful conclusions about what smells attract these insects. It turns out that mosquitoes, like my German uncle, love the smell of beer, Limburger cheese, and pretty perfume. The Limburger cheese research helped explain why they are so drawn to stinky feet (which smell like the cheese—yuck!). They are also drawn to pregnant women, who emit a higher amount of carbon dioxide from their breath, and to people with blood type O. According to research, the insects can smell your blood type before they bite.
To dispel some myths, the following things do NOT deter mosquitoes: eating garlic, vitamin B12, bananas, or mystical campfire dances (sorry kids.) The limited research on back-porch bug zappers suggests they aren’t very effective, either.
Although I don’t plan on having Limburger cheese and beer for dinner, I expect I’ll probably get a few more bites just sitting around the campfire tonight. It’s a reminder that mosquitoes still out-rank me on the evolutionary food chain, and I’m okay with that.
After all, it’s a great excuse to sport my tie-dyed long johns and frumpy camping hat. I’ll take it.