Anopheles gambiae mosquito feeding Mosquitos are flies (their name means "little fly" in Spanish). They first appeared bout 170 million years ago during the age of the dinosaurs, and today they are found in virtually every part of the world. The species that causes yellow fever and malaria are believed to have diverged about 150 million years ago.
There are 3,500 species and subspecies of mosquito, three fourths of which live in the tropics. Once they have left the larval stage, mosquitos typically live 7 to 10 days. Some females live as long as 30 days. If the weather is too hot, mosquitos quickly dehydrate and die. [Sources: Lewis Nielsen, National Geographic, September 1979; David Schwartz, Smithsonian; David Zimmermann, Smithsonian]
Mosquitos are though to transmit more diseases than other creature. They carry over 80 different diseases, including malaria, yellow fever, encephalitis and dengue fever. There are more than 500 known mosquito-borne viruses, but not all of them have harmful affects on humans.
Mosquitos fly at a speeds around 3mph. The buzzing noise produced by mosquitos is generated by wings flapping at a rate of 200 to 500 beats a second. Mosquitos can cover long distances. Some have been captured 100 miles out at sea. They are most vigorous in temperatures above 80°F. They get sluggish at 60°F and disappear when the temperatures drop below 50°F. The can hibernate through the winter and spring back to life when the temperatures warm.
On a day to day basis both sexes feed on flower nectar and fruit juices like other insects. These are the only things that males feed on. Females need protein-rich blood to produce viable eggs. They extract blood not just from humans but from a variety of creatures and are attracted by the body heat, carbon dioxide and the lactic acid and folic acid in the sweat of prey, which they can detect more than a 100 feet away.
Websites and Resources on Health and Diseases: Centers for Disease Control and Prevention cdc.gov/DiseasesConditions ; Disease Pictures hardinmd.lib.uiowa.edu/pictures ; World Health Organization (WHO)statistics and data who.int/research ; World Health Organization (WHO) disease outbreak alert who.int/csr/disease ; Third World Traveler thirdworldtraveler.com/Disease/diseases ; Health Map healthmap.org ; Medline Plus medlineplus/healthtopics ; Merch Manuals (detailed info many diseases) merckmanuals.com/professional/index ; Health Images Directory healthline.com/directory/images
Book: Mosquito: A Natural History of Our Most Persistent and Deadly Floe by Andrew Spielman and Michael D'Antonio (Hyperion, 2001)
Mosquito Mating and Young Mosquitos
Females may go through several cycles of mating, feeding, and egg laying. A stomach full of blood signals the female to start producing eggs. Females mate just once, storing the sperm in special pouch to fertilize several batches of eggs. Each batch requires a new meal of blood. The male dies soon after mating. After ejaculating sperm some mosquitos produces a kind of plug which seals the female's orifice and prevents other males from impregnating the female.
Some species of mosquito lay their eggs directly in water. Others lay them in a dry area expected to flood. In places with human populations, mosquitos often lat their eggs in bird baths, pet dishes, puddles, small pots, potted plants, and old tires. Mosquitos take advantage of every bit of standing water to lay their eggs. That is why there are so many mosquitos in tundra regions, which floods after the spring thaw. Scientists in the Canadian Arctic have recorded attack rates of 9000 bites a minute, enough to cause a person to lose half his blood supply in two hours and cause death.
Generally, within a few days after the eggs are laid they hatch, releasing larvae that swim around, breath through snorkels and survive off organic material. After molting for the fourth time, which occurred about a week after hatching, the larvae becomes pupa which do not eat and float around the water. A few days later the pupa skins break open and a mosquito emerges and flies away and is ready to mate and start the cycle over again.
Mosquitos, Blood and Disease
Only female mosquitos bite. They are capable of carrying three times their body weight in blood. They need the protein and nutrient-rich hemoglobin in the blood to nourish their eggs. One good feeding provides enough nutrients for 75 to 500 eggs. Males have no interest in blood.
To extract blood a female places its proboscis (a long tube that extends from the mouth) in the skin and penetrates the skin with a mandibles that flip out of her mouthpart like switchblade. When the skin is pierced a pair of tubes called fascicles enters the body to search for blood. A mosquito’s proboscis looks like a solid spike but is actually a composite of cutting blades and feeding tubes, powered by two tiny pumps. After taking position on a female drills through layers of epidermis and fat until she reaches blood-filled micro-capillaries and the starts to drink.
Once the a capillary is pierced by the fascicles, two powerful pumps inside the female’s head draw out the blood. Mosquito's saliva contains hundreds of chemicals, including anticoagulants that prevent the blood form clotting and compounds that dilate the capillaries to increase flow. A mosquito often draws its own body weight in blood in one feeding.
Mosquitos have an efficient anticoagulant in their saliva. When mosquitos bite they deposit a protein that keeps the blood from coagulating as they drink it. The body responds by producing histamines to fight off the invaders. It the histamines that cause the skin to swell, turn red and itch.
Speed is critical. The mosquito usually lands, finds the blood and sucks it less than two seconds. Those that linger to long are often swatted and killed. Weighted down by the blood it usually flies some place to rest. There are still things about the process that scientists don’t understand. For example friction should make sucking blood through a feeding tube with an infinitesimally small diameter impossible.
Japanese medical researchers have been able to reduce the pain of an injection by using hypodermic needles edged with tiny serrations, like those on a mosquito’s proboscis, minimizing nerve stimulation.
anopheles pupa For protection from insects use an insect repellant with at 30 percent DEET (some people recommend 95 to 100 percent), wear long pants and long sleeve shirts, treated with "Coulston's Duranon Tick, spray, and sleep under an insecticide-impregnated insect netting. Periodically check your body for ticks. If a tick penetrates your skin, remove the entire tick with tweezers or a tick removal kit by grasping the head and slowly backing it out.
Disease-carrying mosquitos, like most mosquitos, generally bite at night between dusk and dawn, and are particularly fierce around sunset. An exception to this rule are mosquito that carries dengue fever. They generally bite in the day. Mosquitos generally go for the lower extremities of the body. People with a high skin temperature and high moisture-transpiration rates sometimes attract more mosquitos.
anopheles egg The best way to avoid disease-carrying mosquitos and insects is avoid the places where the diseases are known to exist. The Center of Disease Control can provide information on countries and regions where diseases are found. Rural areas are generally more risky than urban areas. Local people can often provide information on specific risky places in their area.
The best way to avoid mosquitos is to: 1) stay inside when they are most active (in the late afternoon, early evening, and early morning); 2) sleep under a mosquito net (tucked under the mattress and treated with an insecticide); 3) cover as much of your body with clothing as possible, wearing long sleeve, light-colored, loose-fitting clothing; 4) use a repellant and your skin and a toxicant on your clothing; and 5) stay in hotels that are well-screened or air-conditioned, if screens are insufficient ask for mosquito netting. Fans and mosquito coils are also effective in keeping mosquitos away. Sandals should be avoid and pants should be tucked into socks in places with lots of ticks. White or light clothing makes ticks easier to spot.
Many Africans who live malaria-endemic areas use nets but still get the disease. Many people in hot countries don't like them because the keep out the breeze.
DEET and Permethrin
Use a DEET insect repellents on your skin. DEET is a strong chemical that interferes with the tiny sensory hairs and pits in the antenna and body it uses to detect carbon dioxide.. DEET is toxic if ingested; stings eyes severely; and can blister the skin in high concentrations. Repellents with 30 to 35 percent DEET are good. They the usually only last for around five hours. Higher concentrations, such a 95 percent to 100 percent, don’t add any more protection but they last longer. Aerosol insecticides and mosquito coils help to clear rooms but they sometimes contain DDT. Non-DEET repellants generally work 1½ hours or less.
The Centers for Disease Control and Prevention recommend products containing DEET, picaridin, IR3535 and the oil of lemon eucalyptus. They say put some on you clothes for greater protection. If you wear sun screen, apply the insect repellant on top of it.
Use a spray or repellent with Permethrin or Permanone (such as Coulston's Duranon Tick Repellent) on your clothes, shoes, tents, camping gear and bed netting. Permethrin often maintains its potency through ten or more washing. It bonds tightly with cotton fabric and It is effective enough to knock out a mosquito by the time sticks its probe through the cloth and it aims it towards the victims skin.
Some people are turned off by the odor of DEET and the chemical os not suited for all ages. Alternatives include the chemical Picaridin and the plant-based oil of lemon eucalyptus.
Scientists want a multi-pronged approach to be used to combat malaria, which includes malaria mosquito eradication, prevention measures like mosquito nets and drug treatments for those with the disease. The main eradication strategy is to throw every known malaria-fighting method at the disease. Health officials say if all tools—such as nets, medicines and DDT—are utilized the number of malaria cases could be reduced by 90 percent.
Important factors in controlling malaria include: 1) the availability of health services: 2) effectively using prevention strategies; 3) effectively using treatment strategies; 4) availability of effective medicines: 5) an effective health surveillance system; 6) limiting climate change; and 7) availability of good housing.
Methods of combating malaria in areas where the disease is common include: 1) systematically eliminating standing water, where mosquitos breed; 2) spraying houses with insecticide; 3) providing people with mosquito netting; and 4) providing people with drugs that prevent and treat the disease. While many remedies seem simple and cheap by the standards of the developed world they are still expensive and beyond the reach of many in the developing world.
Methods that have been employed in places where malaria has nearly been eradicated have included: 1) applying insecticides to the inside walls of homes every six months; 2) collecting family medical histories and GPS data on handheld devises; 3) simplifying treatment by packaging drugs for individual use; 4) setting up mosquito traps and testing the mosquitos for malaria; 5) using the new finger-stick tests to quickly detect who is sick; and 6) getting the sick on artemisinin-based combination therapy quickly.
The easiest way to avoid malaria is to avoid places with the disease and take measures to prevent from being bitten by malaria-carrying mosquitos, which strike primarily in the evening or at night. People who live in areas where malaria is endemic use mosquito netting (preferable treated with insecticide); have screens on their windows; use insect repellent and light mosquito coils in the evenings.
Spaying the insides of houses, particularly with DDT, has proven to be a very effective malaria-fighting measure. Again since malaria mosquitos bite mainly at night spraying the inside of houses where people sleep reduces he chance of getting bitten, Studies have shown that if 80 percent of the houses in a village or neighborhood almost no one gets malaria. Spraying works because people who are bitten are bitten by mosquitos that have not bitten an infected person and thus don’t carry malaria.
Money and Support for Combating Malaria
In July 2008 the Bush administration pledged to spend $48 billion over the next five years to help treat and prevent AIDS, tuberculosis and malaria, with $39 billion to be spent on AIDS, $5 billion on tuberculosis and $4 billion on malaria. Around the same time $3 billion drive to eradicate malaria deaths to near zero was launched in 2008. Among those that supported it are Colgate, Bono, the creator of “American Idol” and the heads of state of several countries.
Some have argued that one thing that has helped malaria thrive in the developing world is the fact that it has been wiped out in the developed world.
Poverty expert Jeffrey Sachs of the Earth Institute of Columbia University has estimated it cost about $4.50 to provide mosquito nets and artemisinin-based drugs for all Africans at risk of malaria, with a total cost of $3 billion necessary to meet the needs of the entire African continent. This is a lot of money for Africa but not that much for the developed world , where $24 billion is paid out in Wall Street Christmas bonuses and millions forked out each day for a $4 Starbucks coffee.
Global Fund to Fight AIDS, TB and Malaria theglobalfund.org
Malaria and Mosquito Nets
SMS_for Life Insecticide-treated mosquito nets are amazingly effective in preventing malaria. They can cut malaria infections by half and child deaths by a third. Studies by the U.S. Center for Disease Control and Prevention indicate that widespread use can reduce transmission by 90 percent.
Insecticide-treated mosquito nets are cheap and easy to use. They cost $5 or less. The cost to manufacture, ship and distribute them is about $10 a piece. They are now cleverly engineered so they can last for five years.
To work mosquito nets need to be installed properly, used regularly and treated every six months to a year with insecticide. The insecticide is more important protecting people from bites than the netting itself. It works by killing mosquitos attracted to the net by the carbon dioxide exhaled from the sleeping people. Not only do treated nets prevent people from getting infected, they reduce the severity of the disease among those who get infected (they have fewer parasites in their blood and less severe fevers).
Nets have been used for some time. Herodotus described Egyptians who wrapped themselves in fishing nets. Nineteenth century British colonists used them in India even before they knew malaria was caused by mosquitos.
About 25 percent of childhood malaria cases could be prevented immediately if children in infected areas used insecticide-treated mosquitos nets. In some parts of Africa mortality rates for children have been reduced by 60 percent by using nets.
Research has shown that people don’t even have to sleep under nets to receive their benefits. A study in Kenya, found that children who didn’t sleep under nets themselves but lived within 300 meters of houses with nets had fewer parasites in their blood and low mortality rates than those who lived in areas with no nets. A study in Ghana showed that mortality rates among children decreased 7 percent every hundred meters closer they lived to houses with nets.
Malaria Net Activism and Entrepreneurship
distribution of malaria nets in Niger Millions of dollars has been spent by international agencies, NGOs and USAID on getting mosquito nets into the hands of people that need them. As of 2007 a group called Nothing But Nets had raised $13 million mainly from young people through web-based marketing and used the money to purchase pesticide-treated mosquitos nets for people who need in the developing world.
The Danish company Vestergaard Frandsen S.A. is the world’s largest producer of insecticide-imbedded mosquito nets. More than 48 million Permanets produced by the company were sold in 2007. The company also makes malaria-fighting, insecticide-coated sheeting (ZeroFly) and has developed a trap for tsetse flies.
Groups involved in handing out malaria nets in high-risk areas and educating people about their use include Against Malaria ( www.againstmalaria.com/netdelivery ); Center for Disease Control Foundation (www.cdcfoundation.org/bednets ); Population Serves International (www.psi.org/malaria ); Malaria No More ( www.malarianomore.org ) ; Nothing But Nets: ( www.nothingbutnets.org )
In April 2010, in honor of World Malaria Day, viewers of American Idol were urged to donate $10 for an insecticide-treated bed net to save an African child from malaria.
Distribution and Use of Mosquito Nets
distribution of malaria nets in Niger Mosquito nets require little infrastructure to distribute. A single volunteer on a motorcycle can give out hundreds of them a day even in the most remote areas, There is no need for refrigerators to keep medicines and vaccines cold. Doctors are not needed to set proper doses. Red Cross volunteers have been quite effective in setting up distribution networks and training villagers in Togo and Niger, where more than half of all households in both countries received nets in a matter of a few days.
Charging net users appears to be a better strategy than giving them out free, presumably because more value is attached to them. In his book The White Man’s Burden: Why the West’s Efforts to Aid the Rest Have Done So Much Ill and So Little Good (Penguin Press), William Easterly describes how when malaria-fighting mosquito nets are given out free “nets are often diverted to the black market...or wind up being used as fishing nets or wedding veils.” When they were sold for $5 a piece in program in Malawi “the nationwide average of children under 5 sleeping under nets” increased “from 8 percent in 2000 to 55 percent in 2004...A follow up survey found nearly universal use of the nets by those who paid for them” while in a Zambian program that handed out nets free “70 percent of the recipients didn’t use” them.
Problems with Using Mosquito Nets
Despite their obvious benefits mosquito nets are still not widely used. As of 2007, only two percent of children in Africa used them. Many people don’t use them because they don’t like them or find them inconvenient. Even at only $5 a pop for many poor families they are still too expensive. Upkeep is also a problem. Reapplication of pyrethrid insecticide is recommended at intervals of 6 to 12 months with older nets, something many villagers don’t have the time or know-how to do.
Many people don’t like to lie under the nets because they are hot or stop using them when the rainy season ends. A tear in the net or a gap or leg hanging out can allow mosquitoes to reach the body.
The tight mesh that keeps mosquitos out also blocks ventilation and makes the nets hot and uncomfortable. Because they are viewed as hassle and malaria is not necessarily considered a serious ailment people didn’t use them. On top of that people believe that malaria is caused by things such as magic or hard work. Some villagers put the nets above their beds but never unwrap them.
Data indicates that in places where Africans have access to mosquito nets half refuse to sleep under them. Even those that use them don’t necessarily use every night over periods of years. Even the best nets wear out after four or five years. After that time will replacements arrive at the villages? Will villagers have to buy them themselves?
Better technology and more money from donor nations are expected to help rectify the situation. Several companies now produce nets with insecticide imbedded in the fibers of the nets that last for five years and don’t need to be sprayed.
Image Source: Centers for Disease Control and Prevention cdc.gov/DiseasesConditions ; Wikimedia Commons
Text Sources: CDC Health Information for International Travel, U.S. Department of Health and Human Services; National Geographic, New York Times, Washington Post, Los Angeles Times, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
© 2009 Jeffrey Hays
Last updated March 2011