In the medical field, mosquitoes are perhaps the greatest scourge of any insect pest. In much of the world, mosquitoes are the number-one public health menace, it being estimated that they transmit disease to more than 69 million people every year. They are a common pest in virtually every corner of the world, since they have evolved to adapt to virtually any climate and condition.

But there's one piece of good news: AIDS is among the diseases they do not transmit. HIV virus is specific to human bodily fluids; it requires blood, sexual fluids, or breast milk to live. That's one disease off the list, but a small comfort when the mosquito is able to give you an astounding array of other diseases, infections, and parasites.

The mosquito-borne diseases are mostly of the zoonotic variety. "Zoonotic" means a disease can be transmitted across multiple species, as opposed to being restricted to one species. Mosquitoes stand alongside fleas, ticks, lice, and other blood-sucking parasites as nature's handiest methods of porting diseases from one creature to the next. It could even be argued that if there were no blood-sucking vermin, there would be no such thing as a zooanotic disease!

The one getting the most attention currently in the United States is the West Nile virus. Almost anything with warm blood seems to be able to play host to a West Nile virus. It's preferred hosts are birds, but it is transmittable to humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, and rabbits, and we're probably going to discover more before the story's over. And of course, the main carriers of West Nile are mosquitoes. West Nile Virus, like HIV, has no known human vaccine at this time. It was first discovered in Uganda in 1937, and first appeared in North America in the year 1999. An interesting fact is that crows are particularly susceptible to it, and so the sudden deaths of many crows in an area is a sign that there could be a local West Nile outbreak. Thus, crows serve as a kind of "canary in a coal mine" warning of a West Nile outbreak.

The list of other diseases that you can catch from a mosquito bite seems to go on forever. Take a deep breath and get ready to say: yellow fever, dengue fever, epidemic polyarthritis, Rift Valley fever, Ross River Fever, and don't forget to mention malaria. Malaria, a historically dangerous menace to the human population, has always been linked to mosquitoes. One historic epidemic in particular was the Panama Canal project, which had trouble with a malaria outbreak. This incident alone contributed to the 27,000 deaths associated with that project.

Now here's one fact that should be on the final exam: What is the link between mosquitoes and elephantiasis? Lymphatic Filariasis, the parasite, is transmitted by mosquito bite as well. This particular infection is limited to tropical regions, and causes symptoms reminiscent of the famous "Elephant Man", although the disease actually affecting the Elephant Man was something different.

The dramatic threat posed by mosquitoes to humans has led to all varieties of drastic measures to ward them off. The things that work are mosquito netting, repellents containing the chemical DEET (N,N-diethyl-meta-toluamide), clothing treated with Permethrin repellents, and citronella candles and torches. Now that we've taken care of what works, the following is a list of urban legends for repelling mosquitoes which most definitely do not work. If you catch a patient relying on one of these methods, inform them that it's been de-bunked.

ULTRASONIC DEVICES: They do not work, not only for mosquitoes, but for repelling anything at all. There is not a single shred of scientific evidence anywhere to show that any living creature on Earth consistently avoids the source of an ultrasonic noise. The U.S. Environmental Protection Agency recently conducted a series of tests spanning two years trying many types of ultrasound devices which are purported to repel mosquitoes. Their testing grounds were the mosquito-ridden area around Chesapeake Bay. Their findings were that not one of the devices had any effect on mosquitoes at all. Various studies have been done in universities which produced the same results. Both the EPA and the U.S. Postal Service have begun prosecuting manufacturers of ultrasonic repelling devices because they are making unsupported claims for their products.

VITAMIN B: Even though vitamin B, particularly B6, has been shown to be effective against other kinds of blood-sucking vermin like fleas, it doesn't work against mosquitoes. Vitamin B works to protect your pet against fleas because it makes the dog's blood and skin taste bad to the fleas. Mosquitoes aren't fazed in the least, even if you douse yourself in a barrel of brewer's yeast.

GARLIC: Why is it that every time you go to look up ways to repel something, garlic always pops up? Why did it have to be the garlic clove at the center of so many legends? Why not celery or oranges or corn syrup? But anyway, garlic doesn't repel mosquitoes either. It is a tasty seasoning, however.

BATS: While bats are marvelous, misunderstood, and endangered species and building a bat house is something you shouldn't discourage, bats, sadly, do not make an effective mosquito-killer. Bats do help farmers by gobbling up a wide range of other destructive insect pests, but mosquitoes constitute less than one percent of a bat's diet. This is because a mosquito simply isn't big enough to satisfy a bat-sized appetite.

INCENSE: Now this is just plain silly. Incense, at least the stick kind which you can buy at the store, attracts mosquitoes rather than repels them. This myth arises from the confusion with citronella candles and torches, which do repel mosquitoes.

BUG ZAPPERS: Oh, no, I hear you cry, those electric purple bug zappers really do kill mosquitoes, I've seen them! Yes, along with completely innocent and even beneficial species such as moths, bees, ladybugs, and dragonflies, and it's the dragonflies which, by the way, really are the greatest natural predators of mosquitoes! If a bug zapper gets a mosquito, it was pure luck that the mosquito just happened to blunder into it. You would need about a hundred of them around you to keep from being bitten.

Good luck in fighting them. Remember that eradicating the mosquito menace is difficult because they were here at least 165 millions years before we were!