Five Very Good Reasons to Swat Those Mosquitoes.

Poor little mosquitoes [wiki]. One minute they’re just minding their own business, stopping to quench their thirst, and then whap! Suddenly their lives come to a screeching halt. Well, don’t feel too sorry for the suckers. Here are five reasons to keep on swatting.

1. Malaria

Malaria [wiki] occurs in more than 100 countries and territories and causes more than 1 million deaths each year. This disease comes from four species of Plasmodium parasites and is transmitted through, you guessed it, mosquito bites.

In each case the mosquito picks up the invader when it bites an infected individual. The parasite than uses the mosquito as a reproduction center and food source (eww). After about a week, enough plasmodium to do some damage accumulates, and a little bit is passed along with the mosquito’s saliva when it bites someone new.

After multiplying in that person’s liver, the parasite causes red blood cells to burst and releases toxins into the blood, making the person feel lousy. Hurray for citronella candles!

2. Dengue Fever and Dengue Hemorrhagic Fever.

These sister diseases [wiki] are caused by four related flaviviruses that use the Aedes aegypti [wiki] mosquito as a flying hypodermic needle.

Although the name flavivirus may sound yummy, a disease that causes you to hemorrhage probably isn’t good dinner conversation. While infection sometimes result in only flulike symptoms, there are 50 - 100 million cases and more than 15,000 deaths from the diseases each year.

The first reported epidemics occurred in Asia, Africa, and North America from 1779 to 1780; however, a current pandemic in Southeast Asia has brought the disease back to the forefront.

The good news is that not all people hemorrhage and many immune systems can fight off the disease. The bad news is that the aegypti mosquito is currently in Texas and the southeastern United States, air travel makes disease movement easier, and there is no vaccine.

Dengue virus

Aedes aegypti

3. West Nile Virus

West Nile virus [wiki] used to be found only in Africa, Eastern Europe, West Asia, and the Middle East. However, in 1999 cases were documented in the northeastern United States. That means that our generation is witnessing this disease’s territory expand.

Culex mosquitoes [wiki] transmit the virus, and birds act as virus reservoirs, where the virus can multiply so more mosquitoes can pick it up. People are known as dead-end hosts because while we do get sick, we don’t pass on the germs.

Short-term symptoms of West Nile fever resemble the flu, and this form of the disease is more common because a healthy immune system can usually fight off the virus. And while West Nile encephalitis affect less than 1% of infected people, it is much more serious. In this form the membranes around the brain became inflamed, which can result in neurological damage or death.

4. St. Louis Encephalitis

If encephalitis is an inflammation of the brain, then St. Louis encephalitis [wiki] refers to big-headed people from the Midwest, right? Actually, the disease is caused by another arbovirus - a virus transmitted by mosquitoes.

The St. Louis part came, presumably, because of cases identified in that city. Symptoms range from fever and headaches to more severe infections resulting in stiffness, stupor, and spastic paralysis.

There was a major epidemic of the disease during 1974 - 1977, but since then outbreaks have been sporadic and small. Like West Nile virus, the virus causing St. Louis encephalitis is a flavivirus passed through birds, which act as growth chambers, and transmitted by the Culex species of mosquitoes. Even though there are only about 128 cases per year, it still sounds like a good excuse for mosquito netting.

Yellow fever virus

Aedes aegypti

5. Yellow Fever

Yellow fever [wiki] is perhaps the strongest advertisement for insect repellent - those infected can go from healthy to dead in three days.

The symptoms include a progression from fever to extremity pain to "black vomit" (vomiting blood clots) to jaundice (making the skin yellow) to death. While not everyone dies, who wants to take that chance?

Before we knew that only mosquitoes transmitted the virus (not human contact), yellow fever caused enforcement of strict quarantines. In 1973 1793 yellow fever practically emptied Philadelphia. During the epidemic 5,000 Philadelphians died in three months, and many people - including notables like George Washington - fled the city in terror.

The development of a vaccine against the disease has reduced the number of cases, but it still occurs widely in Africa and South America.

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From mental_floss’ book Condensed Knowledge: A deliciously Irreverent Guide to Feeling Smart Again, published in Neatorama with permission.

[Update 3/15/07: Original article written by Karen Bernd, Ph.D., professor of biology at Davidson College in Davidson, NC.]

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