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The mosquito terrifying Brazil

Aedes aegypti or Yellow Fever mosquito

The Aedes aegypti or Yellow Fever mosquito is the sole vector for the transmission of chikungunya in the Americas at this time.

It isn’t the largest mosquito, but today it caused the World Health Organization to declare an international public health emergency. Aedes aegypti, the Yellow Fever mosquito, carries and transmits the Zika virus and Zika viral illnesses are being blamed for large numbers of microcephaly cases in Brazil. The illness is also being blamed for increased numbers of cases of Guillain-Barré syndrome in countries such as Columbia and El Salvador.

The Yellow Fever mosquito arrived in the Americas with European colonists and the slave trade. It is now native to the tropics and the warmest, wettest parts of the subtropics.

estimated habitat of the yellow fever mosquito

One map used by the CDC to display the estimated range and habitat of Aedes aegypti, the yellow fever mosquito

The European Centre for Disease Prevention and Control (ECDC) states

The domestic form is often not found further than 100m from human habitations although some studies have shown that breeding habitats can also be found away from human dwellings. Aedes aegypti prefer human habitations as they provide resting and host-seeking possibilities and as a result will readily enter buildings. Their activity is both diurnal and crepuscular.

Graphic showing the cycle of infection between mosquitoes, humans and the dengue virus

The cycle of infection

In a Jan. 18 interview, Dr. Scott Weaver, of the University of Texas Medical Branch, described the process by which mosquitoes including the Yellow Fever mosquito contract and transmit illness. Only female Aedes aegypti bite as part of the reproductive process. If a female bites a human with an illness that has adapted to be transmitted by mosquitoes, she becomes infected. Because of an “innate immunity”, the mosquito contracts the illness but is not killed by it. The pathogen collects in the salivary glands and is passed on to the next human that the female bites.

Dr. Cameron Webb is very familiar with the habits of the Yellow Fever mosquito. In a series of Twitter exchanges, he detailed the behaviors which set it apart from many other mosquito species.

Q. How many times do female mosquitoes lay eggs & need blood meals? If uninterrupted, just 1 feed per clutch or multiple feeds?
A. Changes with species; Aedes aegypti multiple small meals and egg batches, “skip oviposition” w/ one batch laid in multiple places

Q. Presumably multiple hosts then?
A. yes, “strike rate” of transmission likely higher for Aedes aegypti than any other mosquito!

and from an earlier exchange:

A. Ae.aegypti and Ae.albopictus almost exclusively day-time feeders. Experienced it myself, stark difference to other species

Aedes aegypti is known to carry and transmit yellow fever, all four dengue viruses, chikungunya, Zika and other, less common viral illnesses. The exact relationship between Zika viral illnesses and unusual numbers of cases of microcephaly and Guillain-Barré syndrome remains unclear. What is clear is that the illness is rapidly spreading throughout Central and South America, carried and transmitted by Aedes aegypti.

Scott C. Weaver, M.S., Ph.D. is a Professor in the Departments of Pathology and Microbiology & Immunology at the University of Texas Medical Branch, Director of the Institute for Human Infections and Immunity and Scientific Director of the Galveston National Laboratory.

Cameron Webb, Ph.D. is a Hospital Scientist at Westmead Hospital, a Clinical Lecturer in the Department of Medical Entomology at the University of Sydney, and a Medical Entomologist with the government of New South Wales.

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