GENETICALLY MODIFIED MOSQUITO “Aedes aegypti” – INFO

3 years ago by in Biotechnology, Biotechnology, Featured, Genetic, Genetic, Systematics and Taxonomy

The yellow fever mosquitoAedes aegypti is a mosquito that can spread the dengue fever, chikungunya and yellow fever viruses, and other diseases. The mosquito can be recognized by white markings on legs and a marking in the form of a lyre on the thorax. The mosquito originated in Africa but is now found in tropical and subtropical regions throughout the world.

SPREAD OF DISEASE AND PREVENTION

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, Aedes aegypti are attracted to chemical compounds that are emitted by mammals. These compounds include ammonia, carbon dioxide, lactic acid, and octenol. Scientists at the Agricultural Research Service have studied the specific chemical structure of octenol in order to better understand why this chemical attracts the mosquito to its host. They found that the mosquito has a preference for “right-handed” (dextrorotatory) octenol molecules.

Aedes aegypti can also contribute to spread reticulum cell sarcoma among Syrian hamsters.

Male (left) and female (centre and right) Aedes aegypti

Male (left) and female (centre and right) Aedes aegypti

The CDC traveler’s page on preventing dengue fever suggests using mosquito repellents that contain DEET (N, N-diethylmetatoluamide, 20% to 30% concentration, but not more). It also suggests the following:

  1. Although aedes aegypti mosquitoes most commonly bite 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.”
  2. The mosquito’s preferred breeding areas are 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.
  3. Wear long-sleeved clothing and long trousers when outdoors during the day and evening.
  4. Spray permethrin or DEET repellents on clothing, as mosquitos may bite through thin clothing.
  5. Use mosquito netting over the bed if the bedroom is not air conditioned or screened. For additional protection, treat the mosquito netting with the insecticide permethrin.
  6. Spray permethrin or a similar insecticide in the bedroom before retiring.

Although the lifespan of an adult Aedes 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.

Genetic modification

A. aegypti is the subject of investigations that genetically modify the mosquitoes. The modified strain, known as OX513A, requires the antibiotic tetracycline to develop beyond the larval stage and passes this trait onto offspring. Modified males raised in a laboratory will develop normally as they are supplied with this chemical and can be released into the wild. However, their subsequent offspring will find no tetracycline in their environment and will never develop into adults. An Oxford firm, Oxitec, is performing a pilot program in Juazeiro, Brazil to test the effectiveness of these modifications in reducing disease spread. A 2010 study carried one in the Cayman Islands saw the release of over three million OX513A mosquitoes. The wild population of mosquitoes subsequently dropped by 80%.

GENOMICS

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 itsDNA 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 that the species diverged from Drosophila melanogaster (the common fruit fly) about250 million years ago, and that Anopheles gambiae and this species diverged about 150 million years ago.

SCIENTIFIC NAME

The species was first named (as Culex aegypti) in a 1757 publication by Fredric Hasselquist titled Iter Palaestinum (“A Journey to Palestine”). Hasselquist was provided with the names and descriptions by his mentor, Carl Linnaeus. Iter Palaestinum 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 pre-date the starting point for zoological nomenclature in 1758. Nonetheless, the nameAedes aegypti was frequently used, starting with H. G. Dyar in 1920.

In order 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 asAedes (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 aedine mosquitoes to continue to use the traditional names, unless they have particular reasons for not doing so.

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