|Yellow fever mosquito|
|Global Aedes aegypti predicted distribution in 2015. |
Aedes aegypti, the yellow fever mosquito, is a mosquito that can spread dengue fever, chikungunya, Zika fever, Mayaro and yellow fever viruses, and other disease agents. The mosquito can be recognized by white markings on its legs and a marking in the form of a lyre on the upper surface of its thorax. This mosquito originated in Africa, but is now found in tropical, subtropical and temperate regions  throughout the world.
Spread of disease and prevention methods
Aedes aegypti is a vector for transmitting several tropical fevers. Only the female bites for blood, which she needs to mature her eggs. To find a host, these mosquitoes are attracted to chemical compounds emitted by mammals, including ammonia, carbon dioxide, lactic acid, and octenol. Scientists at The United States Department of Agriculture (USDA) Agricultural Research Service have studied the specific chemical structure of octenol to better understand why this chemical attracts the mosquito to its host. They found the mosquito has a preference for "right-handed" (dextrorotatory) octenol molecules.
The mosquito carries a disease that is widespread in tropical South America and Africa, and often come out in moderate regions during the summer time. Today, the Aedes aegypti is found around the southeast region of the U.S., but is slowly decreasing due to competition with other mosquitoes, such as Aedes albopictus.
The Centers for Disease Control and Prevention traveler's page on preventing dengue fever suggests using mosquito repellents that contain DEET (N, N-diethylmetatoluamide, 20% to 30%). It also suggests:
- Although Aedes aegypti mosquitoes most commonly feed at dusk and dawn, indoors, in shady areas, or when the weather is cloudy, "they can bite and spread infection all year long and at any time of day."
- Once a week, scrub off eggs sticking to wet containers, seal and/or discard them. The mosquitoes prefer to breed in areas of stagnant water, such as flower vases, uncovered barrels, buckets, and discarded tires, but the most dangerous areas are wet shower floors and toilet tanks, as they allow the mosquitos to breed in the residence. Research has shown that certain chemicals emanating from bacteria in water containers stimulate the female mosquitoes to lay their eggs. They are particularly motivated to lay eggs in water containers that have the correct amounts of specific fatty acids associated with bacteria involved in the degradation of leaves and other organic matter in water. The chemicals associated with the microbial stew are far more stimulating to discerning female mosquitoes than plain or filtered water in which the bacteria once lived.
- Wear long-sleeved clothing and long trousers when outdoors during the day and evening.
- Use mosquito netting over the bed if the bedroom is not air conditioned or screened, and for additional protection, treat the mosquito netting with the insecticide permethrin.
Insect repellants containing DEET (particularly concentrated products) or p-menthane-3,8-diol (from lemon eucalyptus) were effective in repelling Ae. aegypti mosquitoes, while others were less effective or ineffective in a scientific study. The Centers for Disease Control and Prevention article on "Protection against Mosquitoes, Ticks, & Other Arthropods" notes that "Studies suggest that concentrations of DEET above approximately 50% do not offer a marked increase in protection time against mosquitoes; DEET efficacy tends to plateau at a concentration of approximately 50%".
Mosquito control is currently the best method for disease prevention. This primarily includes source reduction, pesticide spraying for larval control and "fogging" for adult control, or the use of mosquito traps like the lethal ovitrap.
Although the lifespan of an adult Ae. aegypti is two to four weeks depending on conditions, the eggs can be viable for over a year in a dry state, which allows the mosquito to re-emerge after a cold winter or dry spell.
New research is looking into the use of a bacterium called Wolbachia as a method of biocontrol. Studies show that invasion of Ae. aegypti by the endosymbiotic bacteria allows mosquitos to be resistant to the certain arboviruses such as dengue fever and Zika virus strains currently circulating.
Distribution and population control efforts
The yellow fever mosquito's distribution has increased in the past two to three decades worldwide, and it is considered to be among the most widespread mosquito species. Signs of Zika virus-capable mosquito populations have been found adapting for persistence in warm temperate climates. Such a population has been identified to exist in parts of Washington, DC, and genetic evidence suggests they survived at least the last four winters in the region. One of the study researchers noted, " ...some mosquito species are finding ways to survive in normally restrictive environments by taking advantage of underground refugia".
New research has attempted to estimate the basic reproduction number, or R0 value, for Zika virus in several locations. Research looking at the Yap Island epidemic estimated an R0 of 4.3–5.8. R0 value estimates for the Colombia epidemic ranged from 3.0–6.6. Values for both locations were seen to be similar to those found for dengue and Chikungunya virus. Determining these values could help determine transmissibility, as well as how large an area would need to be vaccinated if/when a vaccine is developed, to acquire herd immunity.
Ae. aegypti has been genetically modified to suppress its own species in an approach similar to the sterile insect technique, thereby reducing the risk of disease. The mosquitoes, known as OX513A, were developed by Oxitec, a spinout of Oxford University. Field trials in the Cayman Islands, Brazil, and Panama have shown that the OX513A mosquitoes reduced the target mosquito populations by more than 90%. This mosquito suppression effect is achieved by a self-limiting gene that prevents the offspring from surviving. Male modified mosquitoes, which do not bite or spread disease, are released to mate with the pest females. Their offspring inherit the self-limiting gene and die before reaching adulthood—before they can reproduce or spread disease. The OX513A mosquitoes and their offspring also carry a fluorescent marker for simple monitoring. To produce more OX513A mosquitoes for control projects, the self-limiting gene is switched off (using the Tet-Off system) in the mosquito production facility using an antidote (the antibiotic tetracycline), allowing the mosquitoes to reproduce naturally. In the environment, the antidote is unavailable to rescue mosquito reproduction, so the pest population is suppressed.
The mosquito control effect is nontoxic and species-specific, as the OX513A mosquitoes are Ae. aegypti and only breed with Ae. aegypti. The result of the self-limiting approach is that the released insects and their offspring die and do not persist in the environment.
In Brazil, the modified mosquitoes were approved by the National Biosecurity Technical Commission for releases throughout the country. Insects were released into the wild populations of Brazil, Malaysia, and the Cayman Islands in 2012. In July 2015, the city of Piracicaba, São Paulo, started releasing the OX513A mosquitoes. In 2015, the UK House of Lords called on the government to support more work on genetically modified insects in the interest of global health. In 2016, the United States Food and Drug Administration granted preliminary approval for the use of modified mosquitoes to prevent the spread of the Zika virus.
Another proposed method consists in using radiation to sterilize male larvae so that when they mate, they produce no progeny. Male mosquitoes do not bite or spread disease.
The recent invention of CRISPR/Cas9 based genome editing tool have significantly expanded the scope of genome editing research in Aedes aegypti mosquito. Several scientists across the globe have already attempted this technique to engineer the genome of vector mosquitoes. The genes like ECFP (enhanced cyan fluorescent protein), Nix (male-determining factor gene), Aaeg-wtrw (Ae. aegypti water witch locus), Kmo (kynurenine 3-monoxygenase), loqs (loquacious), r2d2 (r2d2 protein), ku70 (ku heterodimer protein gene) and lig4 (ligase4) were targeted to modify the genome of Aedes aegypti using CRISPR/Cas9 tool to obtain a new mutant, which will become incapable of pathogen transmission or result in population control.
The genome of this species of mosquito was sequenced and analyzed by a consortium including scientists at The Institute for Genomic Research (now part of the J. Craig Venter Institute), the European Bioinformatics Institute, the Broad Institute, and the University of Notre Dame, and published in 2007. The effort in sequencing its DNA was intended to provide new avenues for research into insecticides and possible genetic modification to prevent the spread of virus. This was the second mosquito species to have its genome sequenced in full (the first was Anopheles gambiae). The published data included the 1.38 billion base pairs containing the insect's estimated 15,419 protein-encoding genes. The sequence indicates the species diverged from Drosophila melanogaster (the common fruit fly) about , and Anopheles gambiae and this species diverged about .
The species was first named (as Culex aegypti) in 1757 by Fredric Hasselquist in his treatise Iter Palaestinum. Hasselquist was provided with the names and descriptions by his mentor, Carl Linnaeus. This work was later translated into German and published in 1762 as Reise nach Palästina. Since the latter is an uncritical reproduction of the former, they are both considered to antedate the starting point for zoological nomenclature in 1758. Nonetheless, the name Aedes aegypti was frequently used, starting with H. G. Dyar in 1920.
To stabilise the nomenclature, a petition to the International Commission on Zoological Nomenclature was made by P. F. Mattingly, Alan Stone, and Kenneth L. Knight in 1962. It also transpired that, although the name Aedes aegypti was universally used for the yellow fever mosquito, Linnaeus had actually described a species now known as Aedes (Ochlerotatus) caspius. In 1964, the commission ruled in favour of the proposal, validating Linnaeus' name, and transferring it to the species for which it was in general use.
The yellow fever mosquito belongs to the tribe Aedini of the dipteran family Culicidae and to the genus Aedes and subgenus Stegomyia. According to one recent analysis, the subgenus Stegomyia of the genus Aedes should be raised to the level of genus. The proposed name change has been ignored by most scientists; at least one scientific journal, the Journal of Medical Entomology, has officially encouraged authors dealing with aedile mosquitoes to continue to use the traditional names, unless they have particular reasons for not doing so. The generic name comes from the Ancient Greek ἀηδής, aēdēs, meaning "unpleasant"  or "odious".
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|Wikimedia Commons has media related to Aedes aegypti.|
|Scholia has a topic profile for Aedes aegypti.|
- VectorBase's genomic resource for Aedes aegypti
- Aedes aegypti page from University of Sydney, Australia
- Aedes aegypti and dengue fever
- United States CDC page on dengue fever containing information on prevalence of Aedes aegypti worldwide and past efforts to eradicate it
- Aedes aegypti on the UF / IFAS Featured Creatures Web site
- Walter Reed Hospital Distribution, taxonomy, references etc. Excellent image.
- Aedes aegypti at MetaPathogen: taxonomy, life cycle, facts
- THE ECOLOGY AND BIOLOGY OF Aedes aegypti (L.) AND Aedes albopictus (Skuse) (DIPTERA: CULICIDAE) AND THE RESISTANCE STATUS OF Aedes albopictus (FIELD STRAIN) AGAINST ORGANOPHOSPHATES IN PENANG, MALAYSIA