Lady Mosquitoes: Free Rides for Pathogens

Itchy welts left behind by mosquitoes are one thing, but the microscopic friends they can leave behind are another thing all together

Mosquito-borne diseases have been making national headlines recently through record-breaking numbers of West Nile virus and emerging cases of Eastern equine encephalitis. Though these are certainly newsworthy trends, there is nothing new about how good mosquitoes are at transmitting infectious diseases. It should come as no surprise given all the extra time they've had to evolve.While mosquitoes have been flying around Earth for approximately 220 million years , modern humans emerged only 200,000 years ago. This means that to mosquitoes, we really are nothing but fresh meat. At least to lady mosquitoes.

Female mosquitoes are the only ones interested in feeding on us as they need protein from our blood to develop their eggs. They track us down by scent, visual clues, and heat detection - all so they can use us as a blood meal for the purpose of laying up to 300 eggs. Unlike vampires, mosquitoes don't actually bite. Why are they called mosquito bites? Good question. Instead of biting, they actually pierce our skin with a mouth part called a proboscis. This is basically a needle-like structure that is used to suck our blood.

Since lady mosquitoes are essentially sticking us with used needles* every time they feed on us, it's no wonder they have an affinity for being disease vectors. With all the blood they drink, mosquitoes often slurp up blood-borne pathogens (viruses, bacteria, and parasites that cause illness). These pathogens then get a free ride to a new host without causing any harm to the mosquito, thanks to her anciently refined immune system. Transmission occurs through the mosquito's saliva, which is injected prior to feeding (it contains anticoagulants which are substances that prevent your blood from clotting). In addition to the aforementioned West Nile virus and Eastern equine encephalitis, mosquitoes can also infect humans with several other diseases including:

• Malaria
• Dengue fever
• Western equine encephalitis 
• Japanese encephalitis
• St. Louis encephalitis
• La Crosse encephalitis
• Yellow fever
• Rift Valley fever

The upshot? Not all pathogens survive after they've been ingested by a mosquito and therefore cannot be transmitted to a new host. Thankfully, this is the case for HIV. In case you didn't catch that the first time: mosquitoes do not transmit HIV!

Mosquitoes may have millions of years of evolution in their favor, but our big brains have found some ways to make ourselves seem less tasty to wannabe mama mosquitoes. Here are some ways you can prevent yourself from being used as a blood meal when participating in outdoor activities during mosquito season:

• Use an insect repellent containing DEET, picaridin, oil of lemon eucalyptus (also called PMD), or IR3535.
• Minimize skin exposure and wear light-colored clothing when in mosquito infested areas (e.g. wooded areas or areas with large bodies of standing water).
• Minimize areas of standing water around your home.
• Don't keep windows and doors open unless you have intact screens. 

Another safety measure you can take is to follow recommendations for prophylactic medications and vaccines when traveling to countries with high rates of mosquito-borne diseases.

When I was a teenager I thought smelling like bug spray was worse than putting up with itchy mosquito bites. I would like to officially retract that opinion.

*While the proboscis of a mosquito resembles a needle, a feeding mosquito does not employee the same mechanisms of a hypodermic syringe. Used syringes (also called needles) pose a different set of threats and should not be confused with insects.