Mosquitoes family Culicidae. They have a pair of scaled wings, a pair of halteres, a slender body, and long legs. The females of most mosquito species suck blood (hematophagy) from other animals, which has made them the most deadly disease vectors known, killing millions of people over thousands of years and continuing to kill millions per year by the spread of diseases.^[1][2]

Length varies but is rarely greater than 16 mm (0.6 inch)^[3], and weight up to 2.5 mg (0.04 grain). A mosquito can fly for 1 to 4 hours continuously at up to 1?2 km/h^[4] travelling up to 10 km in a night. Most species are nocturnal or crepuscular (dawn or dusk) feeders. During the heat of the day most mosquitoes rest in a cool place and wait for the evenings. They may still bite if disturbed.^[5]

Contents Feeding habits Mosquito Saliva Mosquitoes and health Mosquito control and integrated mosquito management Mosquito repellents and personal mosquito control Natural Predators Treatment of mosquito bites Cultural views Systematics Identification See also References External links

Feeding habits

Both male and female mosquitoes are nectar feeders, but the female of many species is also capable of haematophagy (drinking blood). Females do not require blood for survival, but they do need supplemental substances (like protein and iron) to develop eggs. Prior to and during blood feeding, they inject saliva. The Toxorhynchites species of mosquito never drink blood.^[6] This genus includes the largest of the extant mosquitoes, the larvae of which are predatory on the larvae of other mosquitoes. These mosquito eaters have been used in the past as mosquito control agents with varying success.^[7]

Female mosquitoes hunt their blood host by detecting carbon dioxide (CO₂) and 1-octen-3-ol from a distance.

Mosquito Saliva

In order for a mosquito to obtain a blood meal it must surmount the vertebrate physiological responses. The mosquito, as with all blood-feeding arthropods, has evolved mechanisms to effectively block the hemostasis system with their saliva which contains a complex mixture of secreted proteins. Mosquito saliva affects vascular constriction, blood clotting, platelet aggregation, inflammation, immunity, and angiogenesis.^[8] Universally, hematophagous arthropod saliva contains at least one anticlotting, one anti-platelet, and one vasodilatory substance. Mosquito saliva also contains enzymes that aid in sugar feeding^[9] and antimicrobial agents to control bacterial growth in the sugar meal.^[10] The composition of mosquito saliva is relatively simple as it usually contains fewer than 20 dominant proteins.^[11] Despite the great strides in knowledge of these molecules and their role in bloodfeeding achieved recently, scientists still cannot ascribe functions to more than half of the molecules found in arthropod saliva.^[11]

It is now well recognized that the feeding ticks, sandflies, and, more recently, mosquitoes have an ability to modulate the immune response of the animals (hosts) they feed on.^[8] The presence of this activity in vector saliva is a reflection of the inherent overlapping and interconnected nature of the host hemostatic and inflammatory/immunological responses and the intrinsic need to prevent these host defenses from disrupting successful feeding. The mechanism for mosquito saliva-induced alteration of the host immune response is unclear, but the data has become increasingly convincing that such an effect occurs. Early work described a factor in saliva that directly suppresses TNF-? release, but not antigen-induced histamine secretion, from activated mast cells.^[12] Experiments by Cross et al. (1994) demonstrated that the inclusion of Ae. aegypti mosquito saliva into naïve cultures led to a suppression of interleukin (IL)-2 and IFN-? production, while the cytokines IL-4 and IL-5 are unaffected by mosquito saliva.^[13] Cellular proliferation in response to IL-2 is clearly reduced by prior treatment of cells with SGE.^[13] Correspondingly, activated splenocytes isolated from mice fed upon by either Ae. aegypti or Cx. pipiens mosquitoes produce markedly higher levels of IL-4 and IL-10 concurrent with suppressed IFN-? production.^[14] Unexpectedly, this shift in cytokine expression is observed in splenocytes up to 10 days after mosquito exposure, suggesting that natural feeding of mosquitoes can have a profound, enduring, and systemic effect on the immune response.^[14]

T cell populations are decidedly susceptible to the suppressive effect of mosquito saliva, showing enhanced mortality and decreased division rates.^[15] Parallel work by Wasserman et al. (2004) demonstrated that T- and B-cell proliferation was inhibited in a dose dependent manner with concentrations as low as 1/7th of the saliva in a single mosquito.^[16] Depinay et al. (2005) observed a suppression of antibody-specific T cell responses mediated by mosquito saliva and dependent on mast cells and IL-10 expression.^[17] A recent study suggests that mosquito saliva can also decrease expression of interferon??/? during early mosquito-borne virus infection.^[18] The contribution of type I interferons (IFN) in recovery from infection with viruses has been demonstrated in vivo by the therapeutic and prophylactic effects of administration of IFN-inducers or IFN,^[19] and recent research suggests that mosquito saliva exacerbates West Nile virus infection,^[20] as well as other mosquito-transmitted viruses.^[21]

Mosquitoes and health

Endemic range of yellow fever in Africa (2005)

Endemic range of yellow fever in South America (2005)

Mosquitoes are estimated to transmit disease to more than 700 million people annually in Africa, South America, Central America, Mexico and much of Asia with millions of resulting deaths. In Europe, Russia, Greenland, Canada, the United States, Australia, New Zealand, Japan and other temperate and developed countries, mosquito bites are now mostly an irritating nuisance; but still cause some deaths each year.^[23] Historically, before mosquito transmitted diseases were brought under control, they caused tens of thousands of deaths in these countries and hundreds of thousands of infections.^[24] Mosquitoes were shown to be the method by which yellow fever and malaria were transmitted from person to person by Walter Reed, William C. Gorgas and associates in the U.S. Army Medical Corps first in Cuba and then around the Panama Canal in the early 1900s.^[25][26] Since then other diseases have been shown to be transmitted the same way.

The mosquito genus Anopheles carries the malaria parasite (see Plasmodium). Worldwide, malaria is a leading cause of premature mortality, particularly in children under the age of five, with around 5.3 million deaths annually, according to the Centers for Disease Control. Some species of mosquito can carry the filariasis worm, a parasite that causes a disfiguring condition (often referred to as elephantiasis) characterized by a great swelling of several parts of the body; worldwide, around 40 million people are living with a filariasis disability. The viral diseases yellow fever and dengue fever are transmitted mostly by Aedes aegypti mosquitoes. Other viral diseases like epidemic polyarthritis, Rift Valley fever, Ross River Fever, St. Louis encephalitis, West Nile virus (WNV), Japanese encephalitis, La Crosse encephalitis and several other encephalitis type diseases are carried by several different mosquitoes. Eastern equine encephalitis (EEE) and Western equine encephalitis (WEE) occurs in the United States where it causes disease in humans, horses, and some bird species. Because of the high mortality rate, EEE and WEE are regarded as two of the most serious mosquito-borne diseases in the United States. Symptoms range from mild flu-like illness to encephalitis, coma and death.^[27] Viruses carried by arthropods such as mosquitoes or ticks are known collectively as arboviruses. West Nile virus was accidentally introduced into the United States in 1999 and by 2003 had spread to almost every state with over 3,000 cases in 2006.

A mosquito's period of feeding is often undetected; the bite only becomes apparent because of the immune reaction it provokes. When a mosquito bites a human, she injects saliva and anti-coagulants. For any given individual, with the initial bite there is no reaction but with subsequent bites the body's immune system develops antibodies and a bite becomes inflamed and itchy within 24 hours. This is the usual reaction in young children. With more bites, the sensitivity of the human immune system increases, and an itchy red hive appears in minutes where the immune response has broken capillary blood vessels and fluid has collected under the skin. This type of reaction is common in older children and adults. Some adults can become desensitized to mosquitoes and have little or no reaction to their bites, while others can become hyper-sensitive with bites causing blistering, bruising, and large inflammatory reactions, a response known as Skeeter Syndrome.

Mosquito control and integrated mosquito management

There are two kinds of mosquito control: large, organized programs to reduce mosquito populations over a wide area, and actions individuals can take to control or exclude mosquitoes with respect to themselves and their own property.

Organized mosquito control programs today draw on the principles of integrated pest management. An integrated mosquito control program typically includes the following measures, all guided by surveillance of mosquito populations and knowledge of the mosquito life cycle:^[28]

• source reduction - the removal of mosquito breeding habitats
• habitat modification - manipulating habitats to reduce breeding or access
• biocontrol - introducing natural predators of mosquitoes
• larvicide - using pesticides to reduce larval populations
• adulticide - using pesticides to reduce adult populations

Some solutions for malaria control efforts in the third world are: mosquito nets (klamboe), mosquito nets treated with insecticide (often permethrin), and DDT.^[29] Nets are treated with insecticide because mosquitoes can sometimes get past an imperfect net. Insecticide-treated nets (ITN) are estimated to be twice as effective as untreated nets in preventing mosquito bites.^[30] Untreated mosquito nets are less expensive, and they are effective in protecting humans when the nets do not have any holes and are tightly sealed around the edges. Insecticide free nets do not adversely affect the health of natural predators such as dragonflies.

The role of DDT in combating mosquitoes has been the subject of considerable controversy. While some argue that DDT deeply damages biodiversity, others argue that DDT is the most effective weapon in combating mosquitoes and hence malaria. While some of this disagreement is based on differences in the extent to which disease control is valued as opposed to the value of biodiversity, there is also genuine disagreement amongst experts about the costs and benefits of using DDT. Moreover, DDT-resistant mosquitoes have started to increase in numbers, especially in tropics due to mutations, reducing the effectiveness of this chemical.

Mosquito repellents and personal mosquito control

A mosquito net

One of the main, non-chemical ways to prevent mosquito bites is the mosquito net. Mosquito netting if properly used and maintained (no holes), provides the maximum possible personal protection against biting insects. In many areas of the world, mosquitoes are not only a nuisance, but also pose a serious health threat. Sleeping under a bednet is highly recommended by the World Health Organization (WHO)^[31] and the U.S. Center for Disease Control (CDC)^[32] if staying in these areas.

One of the most popular chemical skin treatments is N,N-diethyl-meta-toluamide, commonly known as DEET. It has been used widely since its invention by the U.S. Department of Agriculture in 1945. DEET products have been widely used for many years but these products have occasionally been associated with some minor to moderate adverse reactions. DEET concentrations in repellents range from 5% up to 100%.

Other less commonly used mosquito repellents include: catnip oil extract, nepetalactone (no known credible tests), citronella 10% solution (84% effective for about 1 hour), or eucalyptus oil extract.^[33] A soybean oil-based product worked for about 1.5 hours and a lemon eucalyptus-based solution worked for about 3 hours.

Picaridin, first used in Europe in 2001, has been reported to be effective by Consumer Reports (7% solution)^[34] and the Australian Army (20% solution).^[35] Consumer Report retests in 2006 show that a 7% solution of picaridin now has a protection time of about 0 minutes and a 15% solution was only good for about one hour.^[36] So far DEET is the champion effective repellent against mosquitoes, especially when worn in conjunction with light coloured clothing, long sleeved pants and shirts and a hat.

Mosquitoes use carbon dioxide (CO₂) and 1-octen-3-ol from human and animal breath and sweat as odor cues and DEET inhibits the detection of the latter in insects.^[37] Other potent body and breath odor cues include lactic acid, dimethyldisulfide,and acetone^[38].

Other commercial products offered for household mosquito "control" include small electrical mats, mosquito repellent vapor, DEET-impregnated wrist bands, and mosquito coils containing a form of the chemical allethrin. Mosquito-repellent candles containing citronella oil are sold widely in the U.S. All of these have been used with mixed reports of success and failure. Some claim that plants like wormwood or sagewort, lemon balm, lemon grass, lemon thyme and the mosquito plant (Pelargonium) will act against mosquitoes. However, scientists have determined that these plants are ?effective? for a limited time only when the leaves are crushed and applied directly to the skin.^[39]

There are several, widespread, unproven theories about mosquito control such as the assertion that Vitamin B, in particular B1 Thiamine, garlic, ultrasonic devices, incense, can be used to repel or control mosquitoes.^{[40] [41]} Moreover, some manufacturers of "mosquito repelling" ultrasonic devices have been found to be fraudulent,^[42] and their devices were deemed "useless" in tests by the UK Consumer magazine Which?^[43]

Bug zappers kill a wide range of flying insects including many beneficial insects that eat mosquitoes as well as some mosquitoes. Bug zappers have not been proven effective at controlling overall mosquito population.

Some newer mosquito traps or known mosquito attractants emit a plume of carbon dioxide together with other mosquito attractants such as sugary scents, lactic acid, octenol, warmth, water vapor and sounds. By mimicking a mammal?s scent and outputs, female mosquitoes are drawn toward the trap, where they are typically sucked into a net or holder by an electric fan where they are collected. According to the American Mosquito Control Association,^[44] "these devices will, indeed, trap and kill measurable numbers of mosquitoes," but their effectiveness in any particular case will depend on a number of factors such as the size and species of the mosquito population and the type and location of the breeding habitat. They are useful in specimen collection studies to determine the types of mosquitoes prevalent in an area but are typically far too inefficient to be useful in reducing mosquito populations.

Natural Predators

Dragonflies are natural predators of mosquitoes.

Treatment of mosquito bites

Visible, irritating bites are due to an immune response from the binding of IgG and IgE antibodies to antigens in the mosquito's saliva. Some of the sensitizing antigens are common to all mosquito species, whereas others are specific to certain species. There are both immediate hypersensitivity reactions (Types I & III) and delayed hypersensitivity reactions (Type IV) to mosquito bites (see Clements, 2000). There are several commercially available anti-itch medications. These are usually orally or topically applied antihistamines and, for more severe cases, corticosteroids such as hydrocortisone and triamcinolone. Many home remedy and recipes exist, most of which are effective against itching, including calamine lotion, baking soda, salt, rubbing alcohol, vinegar. Ammonia has been clinically demonstrated to be an effective treatment^[47].

Scratching, cooling, and heat are effective but bring relief only during the application, although scratching a mosquito bite usually serves to irritate and inflame the area further and increase the risk of infection and scarring.

Applying streaming hot water to bitten areas can immediately eliminate itching if carried out for several minutes. However, this method is only a home remedy and not proven to work on every bite.

Cultural views

According to the ?Mosquitoes? chapter in Kwaidan: Stories and Studies of Strange Things, by Lafcadio Hearn (1850?1904), mosquitoes are seen as reincarnations of the dead, condemned by the errors of their former lives to the condition of Jiki-ketsu-gaki, or "blood-drinking pretas".^[48]

The Babylonian Talmud (Gittin 56b) asserts that the Roman Emperor Titus was punished by God for having destroyed the Temple in Jerusalem by having a mosquito fly into Titus' nose, picking at his brain, ceaselessly buzzing, driving him crazy and eventually causing his death. No such account appears in any Roman source. Titus died prematurely from unclear causes after only two years in power.

Systematics

• Subfamily Anophelinae

• Anopheles

• Cellia

• Bironella

• Chagasia

• Subfamily Culicinae

• Subfamily Toxorhynchitinae

• Toxorhynchites

Identification

• Brunhes, J.; Rhaim, A.; Geoffroy, B. Angel G. Hervy P. Les Moustiques de l'Afrique mediterranéenne French/English. Interactive identification guide to mosquitoes of North Africa, with database of information on morphology, ecology, epidemiology, and control. Mac/PC Numerous illustrations. IRD/IPT [12640] 2000 CD-ROM. ISBN 2-7099-1446-8 Mosquito species can also be identified through their DNA, however this is relatively expensive so it is not commonly performed. See the Use of DNA in forensic entomology.

See also

• Insect repellent
• Cymbopogon
• Anti-itch drug

References

External links

• Mosquito Pest Control Information - National Pesticide Information Center
• West Nile Virus Resource Guide - National Pesticide Information Center
• Mosquitoes of Wisconsin
• Biological Database for Anopheline Mosquitoes
• Database for Disease Vectors
• Inland Floodwater mosquito ''Aedes vexans'' diagnostic photographs and taxonomy
• University of Florida Public Health Pesticide Applicator Training Manual - Chapter on Mosquitoes
• Vertical Flight Capabilities of Mosquitoes
• Mosquito Genomics WWW Server
• Mosquitoes - Micscape September 2003
• CDC Division of Vector-Borne Infectious Diseases - Information on West Nile virus as well as other mosquito- and tick- bourne diseases.
• Florida Medical Entomology Laboratory - A mosquito identification key, along with other helpful information.
• Mosquito photographs from NSW (New South Wales, Australia) Arbovirus Surveillance
• Walter Reed Biosystematics Unit. - Links to the online mosquito catalog, keys for mosquito identification, images and information on medically important species and much more.
• Repellents, Traps, Virus Information, Maps, etc Florida and National information

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