Wolbachia and The Biological Control of Dengue Virus
By: Elisa Xiao
Introduction
Dengue virus is a mosquito-borne disease that causes an enormous health burden to people living in tropical and subtropical regions. No effective vaccine is yet available. Traditional methods for controlling the spread of mosquito-born disease, such as using bed nets and draining wetlands, failed to control the spread of dengue virus by the Aedes aegytpi mosquitoes because they bit during the days and only occupy urban areas. [1] [2] The transinfection of mosquitos with certain strains of the maternally inherited, endosymbiotic bacteria Wolbachia seems to be a new approach in controlling the spread of dengue virus. Certain strains of this bacterium can invade and sustain themselves in wild mosquito populations, affect mosquito reproduction, reduce lifespan of its host, and interfere with pathogen replication.
Dengue virus
Dengue is the most rapidly spreading mosquito-borne viral disease in the world. According to the latest report by the World Health Organization (WHO), an estimated 50-100 million dengue infections occur annually and approximately 2.5 billion people live in dengue endemic countries. [3] [4]
Structure
Dengue virus (DENV) is a small single-stranded positive sense RNA virus comprising four distinct serotypes (DENV-1 to -4). The virion of the dengue virus is enveloped, spherical with a diameter of 50nm. The surface proteins are arranged in an icosahedral-like symmetry. The immature virions contain a membrane protein precursor which is cleaved into two virus-encoded membrane proteins (M and E) once it matures. [3] [5]
The vectors
The various serotypes of the dengue virus are transmitted to humans through the bites of dengue-infected Aedes mosquitoes, mainly Aedes aegypti. This mosquito is commonly found in the tropical and subtropical regions and it is widely distributed around the world, mostly between latitudes 35°N and 35°S below an elevation of 1000 metres. These mosquitoes live in water-filled habitats and prefer to live in and around human habitations. [3]
The host
Humans are the primary host of the virus. Although most infections are asymptomatic or subclinical, in severe cases patients can develop plasma leakage, bleeding, or organ impairment in liver, heart and the central nervous system. Primary infection can induce lifelong protective immunity to the infecting serotype, but only short-term immunity to the other serotypes. [3]
Transmission
Female mosquitoes take up dengue virus during feeding on blood of viraemic human. The viruses then infect the female mosquitoes’ mid-gut and replicate in various tissues before infecting the salivary glands, where the virus can then pass on to other humans during feeding. This extrinsic incubation period (EIP) usually takes about 8-12 days.[3]
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