Mosquitoes aren't just annoying, they spread killer diseases, as well. They are often called one of the most dangerous animals on the planet.
That's right: The most dangerous animals on the planet can be killed with a single swat — but if they've had time to bite, they may have already transmitted a fatal disease.
Illnesses transmitted by mosquitoes and their ilk kill more than a million people each year and infect more than a billion, causing debilitating pain, brain damage, blindness, and other serious effects.
Half of the world population is considered at-risk for diseases transmitted by blood-sucking bugs like ticks, sandflies, and mosquitoes. For World Health Day 2014, the World Health Organization (WHO) wanted to highlight that very real risk with a snappy slogan: "small bite, big threat."
Globally, the deadliest of the creatures that carry and cause these diseases is the mosquito. Here are 10 scientifically valid reasons why they are the worst.
1. Mosquitoes put 40% of the world at risk for dengue, which causes "the feeling of broken bones."
Dengue fever hurts so much that it's commonly referred to as break bone fever.
It's the most rapidly spreading mosquito-borne disease in the world, with 40% of the world currently at risk. Between 50 and 100 million people get dengue every year, and even though it's not usually fatal, it still is a leading cause of death for children in certain Latin American and Asian countries.
The disease can also develop into severe dengue, a hemorrhagic condition that is much more dangerous, causing bleeding, organ impairment, and persistent vomiting.
There's no medicine or vaccine for dengue. Treatment generally involves just trying to keep patients hydrated.
2. Mosquitoes spread yellow fever, which the WHO calls "the original viral haemorrhagic fever."
Yellow fever infects around 200,000 people a year — and kills 30,000. It's a viral hemorrhagic fever that has no treatment. After a period of severe illness, most patients recover, but about 15% enter a toxic phase, when they start to bleed internally and organs begin to fail. About half of patients who enter the toxic phase die.
Cases of yellow fever have been increasing since the 1980s due to declining human immunity, deforestation, climate change, increased air travel, and higher infection rates in cities due to a particular breed of mosquito called the Aedes aegypti.
However, there is an effective vaccine for the fever — one dose provides life-long immunity, and many countries won't permit travelers to enter without proof of vaccination.
3. Mosquitoes are behind the recent outbreaks of chikungunya, which can sometimes lead to agonizing pain.
The painful and potentially debilitating virus chikungunya has been around for centuries, but just appeared in the Americas for the first time at the end of 2013.
The disease's name comes from a word in a Tanzanian language that means "to become contorted," referring to the severe joint pain that it causes, which lasts for weeks, and in some rare cases, even months and years.
The first cases were reported on the island of Saint Martin, but since then, cases have occurred in Martinique, Guadeloupe, Saint Barthelemy, the British Virgin Islands, and the Dominican Republic.
Humans have very little natural immunity to chikungunya, which has allowed mosquitoes to spread the virus quickly throughout populations. In 2005, an outbreak sped through the island of La Reunión, sickening 200,000 of 750,000 residents, despite the fact that the only mosquitoes there, the Asian Tiger Mosquitoes, should not have been able to transmit the virus. Experts realized that it had mutated, allowing Asian Tiger mosquitoes to spread the disease.
4. Mosquitoes scoff at national borders, turning isolated cases into outbreaks.
Any person infected with a mosquito-borne disease can carry it to a different country, where it can spread if they are bitten by a local mosquito upon arrival — which happens frequently.
In 2007, an older Italian man returned home from a trip to India, unknowingly having been bitten by a mosquito carrying chikungunya. Upon returning home, he visited a cousin — and within 3 months, more than 200 people had been infected with the disease.
5. Mosquitoes don't play fair: They target some people more than others.
Some people really are mosquito magnets. Mosquitoes are drawn to the smell given off by the bacteria that live on everyone's skin, and some people give off an odor that makes them especially attractive to the tiny beasts. And contrary to what a lot of people say, eating garlic and using natural repellent doesn't do much, if anything, though DEET-containing bug repellents are indeed effective.