Bad Bugs of Summer: Mosquitoes
Summer is more than lemonade and swimming pools. It means bug bites – mosquitoes, ticks, horse flies, you name it. This is the first in a series of posts profiling these bad bugs of summer: what they do, why they do it, tips on how to protect yourself, and the occasional trivial factoid. We’re starting the series with public enemy number one: mosquitoes.
For starters, there are more than 2,000 species of mosquito worldwide – estimates range from 2,500 to 3,500 or more. More than 150 of those species can be found in the U.S., and 60 of them can be found in North Carolina alone. But they’re not all bad guys. Only 10-15 of the species found in North Carolina bite people.
In fact, many mosquitoes pose no threat to humans at all. Specifically, the males. Male mosquitoes feed on nectar and other sources of sugar. Females are the ones you have to worry about.
While females of some mosquito species do not drink blood, most do. They use the blood as an energy source, or to provide the proteins and lipids they need to develop their eggs.
For example, the Asian tiger mosquito, or Aedes albopictus, feeds on all kinds of mammals – including humans – and uses the blood for energy and reproduction. The albopictus is thought to have come to the U.S. from Japan in the 1980s, and it has made itself at home. It lays its eggs in water-filled containers near homes or in woodlands, and its eggs are robust enough to survive winter weather.
But why do mosquitoes bite us? And what is it about mosquito bites that drives us nuts? Mosquitoes are drawn to the carbon dioxide that we exhale when we breathe. They land on us and probe our skin, puncturing it with their needle-like mouthparts. This does two things. First, the mouthparts lacerate capillaries in our skin, releasing adenosine triphosphate (ATP) from injured cells. The ATP then stimulates the mosquito’s feeding behavior. Second, the mouthparts inject saliva into our blood. The saliva contains a biochemical mixture that prevents the blood from clotting by stopping platelets from sticking together.
The mouthparts damage nerve cells in the skin, causing pain, and the platelets respond to the biochemicals in the saliva by releasing histamines. Those histamines cause additional nerve injury that results in more pain and that annoying itching sensation that accompanies mosquito bites. The swelling associated with mosquito bites stems from the physical tissue damage caused by the mouthparts, and the pooling of blood in the area due to the anticoagulants in the saliva.
But mosquitoes are more than just an annoying summer interloper. They are a vector for a host of life-threatening diseases, including malaria and dengue, which claim more than one million lives each year. Here’s an example of how that works. Our friend albopictus is a known vector for dengue fever. When albopictus bites someone infected with dengue fever, it takes in the virus that causes the disease (actually, any of four viruses, if you want to be particular). The virus penetrates the mosquito’s midgut during digestion and reproduces in its blood, ultimately colonizing the mosquito’s salivary glands. When the mosquito injects its saliva into a future victim, it is unwittingly injecting a fresh batch of dengue virus. Because the saliva prevents the victim’s blood from clotting, the virus is able to get into the victim’s bloodstream.
The best way to avoid mosquito bites is to avoid having mosquitoes around your house. That means eliminating standing water, if you can. Emptying the bird bath, for instance. Another option is to use so-called “mosquito dunks.” These donut-shaped disks are available at most hardware stores and are placed in standing water that you can’t (or won’t) get rid of, such as a rain barrel. Mosquito dunks release a bacterial toxicant that kills mosquito larvae, but won’t harm children, pets or even most other insects (such as butterflies or honeybees).
It is also a good idea to use insect repellent when you’re spending time outdoors. Contrary to what you may have heard, there are a variety of repellents that work, in addition to DEET. The CDC’s list of repellents that provide sufficient protection include DEET, Picaridin, Oil of Lemon Eucalyptus and IR3535. But, with any of these repellents, you don’t want to over-apply – especially with kids. If it’s an aerosol spray, spray it onto your hands and then apply it to the skin. And if the repellent isn’t working, just put on a little more. Don’t douse yourself liberally and keep re-applying. You want just enough to work, not overkill.
If, despite your best efforts, you get some nasty mosquito bites, there are things you can do to minimize your suffering. Put an icepack on the bite, take an oral antihistamine (make sure you take the correct dosage), and put some topical cortisone cream on the bite site to promote healing.
Lastly, if you think that mosquitoes like you more than they like your friends and family – you may be right. Researchers have found that some people are more attractive to mosquitoes than others – though they don’t know why. They know it has something to do with the blend of chemicals that we release through our skin, but no one is quite sure what the magic combination is that makes some people irresistible to the little blood suckers. Whatever it is, it’s a cologne I don’t want.
Note: Many thanks to Dr. Charles Apperson, William Neal Reynolds Professor Emeritus of Entomology at NC State, for taking the time to talk to me about mosquitoes. Apperson, whose work focuses on vector biology, ecoepidemiology and ecology of mosquitoes and ticks, was patient in his explanations, and kindly answered all of my questions (even the inane ones). Any errors in the above post are mine and mine alone.