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Saturday, October 24, 2015

MDB Series - Dengue Part 2

This post is second in the series about mosquito borne diseases.

Disclaimer: This post is for information purposes only. This is not written by any medical doctor or government official or anyone related to the worldwide research on mosquito borne diseases. Neither is this a complete information about dengue and should not be relied on for reference. However, we have taken care to refer to reliable sources on the web, the links to which would be provided at the end of the post.



Causes and Transmission

Dengue is caused by group of RNA virus called Flavivirus. They are of the same genus as many viruses that cause other dangerous diseases like, Japanese encephalitis, West Nile fever, yellow fever etc. All these viruses are called arbo viruses since they are spread by arthropods (mosquitoes, ticks etc)

There are five strains of this dengue virus, the fifth one announced as recently as 2013. The first four and most commonly known are DENV-1, DENV-2, DENV-3, DENV-4. Their difference is in their antigens. Though humans are the main host for this virus they circulate in other primates as well.

The dengue virus is typically spread by the aedes mosquito, especially Aedes aegypti. This mosquito species is mostly found in the tropical region. They bite during the day, particularly at dawn and dusk. They are sincere in their job of spreading disease, that they work double shift, night and day.

Dengue is spread by other Aedes mosquitoes like Aedes polunesiensis, Aedes albopictus, Aedes scutellaris etc. Of these, due to increased globalisation and industrialisation Aedes albopictus has now spread to temperate regions. It is able to survive in the colder climate of Europe because of higher tolerance to the sub-zero temperatures, hibernation etc.

It is possible to get infected with the first bite itself. As is always the case with mosquito borne diseases, the mosquito spreads dengue from an infected person. In this cases, the disease does not needed to have matured. If a person is infected with the virus still in the initial 2 to 10 day period and a mosquito bites that person, the virus could still be spread to other people. This is because, once the virus bites the infected person it becomes itself infected for life, thus spreading dengue virus as long as it lives. Though the mosquito is infected it is not seriously affected by the virus.

Aedes aegypti mosquito is the primary vector of this disease. A.aegypti and A.albopictus mainly are found in urban habitat where they can easily find humans nearby to feed and breed in stagnant water in artificial storage areas (like water collected in used tyres, broken vessels, open water tanks etc) which are abundant. The female aegypti mosquito feeds on multiple humans per feeding cycle, thus spreading the virus more.

Dengue virus are transmitted via mosquitoes. Person to person transmission is so rare and unusual that it is almost unheard of. However, there have been cases where dengue was transmitted through blood transfusion, organ transplantation, from mother to child during pregnancy or at birth.

Sources: Dengue Virus NetWHOWebMDWikipediaMedindiaUS National Library of MedicineMinistry of Health and Family Welfare( Govt of India)

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