DENGUE FEVER


Description of virus

- The Dengue virus is a mosquito-born Flavivirus
- The virus has a genome of about 11 000 bases that codes for three structural proteins, seven nonstructural proteins and short non-coding regions on both the 5' and 3' ends.
- The Dengue virus is a single stranded RNA positive-strand virus
- The Dengue virus is 50-nm
- An enveloped virus with a lipid membrane
- The structural proteins are the capsid (C) protein, the envelope (E) glycoprotein and the membrane (M) protein.
- Has a "crystal" structure

Dengue Virus
Dengue Virus

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The Dengue Virus; Magnified.


Viral Specificity:

- The life cycle of dengue involves endocytosis (the process by which cells absorb molecules from outside the cell by engulfing them with their plasma membrane.) This happens when the macrophage eats the Dengue virus.
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Endocytosis


-When the virus is in its infectious form the surface is smooth, but as it is exposed to the acidic environment of the cell causes the proteins to snap into a trimeric spike so as to penetrate and then fuze with the lysozome membrane.
- After the lysozome membrane has been penetrated the RNA is injected and the infection begins
- After a person is infected with dengue, they develop an immune response that produces specific antibodies that prevent the virus from binding to macrophage cells and gaining entry.
-However, if another subtype of dengue virus infects the individual, the virus will activate the immune system to attack it as if it was the first subtype, producing the same antibodies as before, unfortunately these do not work on the subtype.
- The immune system is tricked because the four subtypes have very similar surface antigens. The antibodies bind to the surface proteins but do not inactivate the virus.
- The human body is dependant on the right antibody response, and because it is not the right response the virus is not inactivated.
- The immune response attracts numerous macrophages and the virus proceeds to infect them.
- This makes the viral infection much more acute, and the body begins to release cytokines (small cell-signaling protein molecules that are secreted by the glial cells of the nervous system) which causes the endothelial tissues (the layer of cells lining the interior surface of all blood vessels, from the heart to the smallest capillary) to become permeable, it then turns into Dengue Haemorrhagic Fever, which is deadly.

Dengue Video (How the Virus infects the cell)
SYMPTOMS AND PROGRESSION:
-After being bitten by a mosquito carrying the virus, the incubation period ranges from three to 15 (usually five to eight) days before the s signs and symptoms of dengue appear.
-Dengue starts with chills, headache, pain upon moving the eyes, and low backache.
-Painful aching in the legs and joints occurs during the first hours of illness.
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Initial Symptoms

-A fever then appears with a temperature as high as 104 F (40 C), with relative low heart rate and low blood pressure.
-The eyes become reddened.
-A flushing or pale pink rash comes over the face and then disappears.
-The glands (lymph nodes) in the neck and groin often swell.
-Fever and other signs of dengue last for two to four days, followed by a rapid drop in body temperature with profuse sweating.
-This precedes a period with normal temperature and a sense of well-being that lasts about a day.
-A second rapid rise in temperature follows. A characteristic rash appears along with the fever and spreads from the extremities to cover the entire body except the face.
-The palms and soles may be bright red and swollen.

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The classis Dengue rash

COMPLICATIONS

-Dengue hemorrhagic fever (DHF) is a specific syndrome that tends to affect children under 10 years of age. It causes abdominal pain, hemorrhage (bleeding), and circulatory collapse.
-DHF starts abruptly with high continuous fever and headache.
-There are respiratory and intestinal symptoms with sore throat, cough, nausea, vomiting, and abdominal pain.
-Shock occurs two to six days after the start of symptoms with sudden collapse, cool, clammy extremities, weak pulse, and blueness around the mouth .
-In DHF, there is bleeding with easy bruising, blood spots in the skin, spitting up blood, blood in the stoo, bleeding gums, and nosebleeds.
-Pneumonia is common, and inflammation of the heart may be present.
-Causes fatlaities in 6% - 30% of victims, most of them children.
-Needs to be monitored closely
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A child with Dengue Hemorrhagic Fever


Common Methods of Transmission:


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The Striped Aedas Mosquito

- Virus is aquired by mosquitos when they feed on infected person
- Virus is then transmitted to other people through mosquito bites
- Only female Aedas mosquitos may aquire the virus

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Treatment and Prevention :
- Because dengue fever is caused by a virus, there is no specific medicine or antibiotic to treat it.
- For typical dengue, the treatment is purely concerned with relief of the symptoms (symptomatic).
- Rest and fluid intake are important.
- Aspirin and nonsteroidal anti-inflammatory drugs should only be taken under a doctor's supervision because of the possibility of worsening hemorrhagic complications.
- Acetaminophen (Tylenol) and codeine may be given for severe headache and for the joint and muscle pain
- Health care from physicians and nurses can decrease mortality rates using fluid replacement therapy
- No vaccine but progress is underway
-The emphasis for dengue prevention is on sustainable, community-based, integrated mosquito control
- Only way to to prevent transmission is to combat the disease-carrying mosquitoes.
  • Preventing water accumulating for mosquito larvae to be laid in.
  • Using insecticides to larval habititats
  • Using Mosquito repellant with DEET

Miscellaneous:
- About two fifths of the world's population is at risk
- Esimated 50 million dengue infections world wide each year
- Estimated 500 000 with DHF require hospitalization, 2.5% die
- Now endemic in more then 100 countries
- Before 1970 only 9 countries experienced DHF epedemics
- Extremly rare cases, dengue virus has been transmitted in organ transplants and blood transfusions from infected persons
- Orginated from monkeys and independatly jumped to humans 100-800 years ago
- Areas at high risk are tropics and subtropics. Such as the Caribbean, including Puerto Rico, the U.S. Virgin Islands, Cuba, and Central America. Cases have also been imported via tourists returning from areas with widespread dengue, including Tahiti, Singapore, the South Pacific, Southeast Asia, the West Indies, India, and the Middle East (similar in distribution to the areas of the world that harbor malaria and yellow fever).
-Dengue is now the leading cause of acute febrile illness in U.S. travelers returning from the Caribbean, South America, and Asia.
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Resources accessed:

Author of Article: Unknown
Title of Article: Dengue Fever
URL: http://denguevirus.net/dengue-virus.html
Date: October 24/2010
Author of Article: John P. Cunha. DO/ Melissa Conrad Stopples MD
Title of Article: Dengue Fever
URL: http://www.medicinenet.com/dengue_fever/article.htm
Date: July 7/2010

Author of Article: Unknown
Title of Article: Dengue Fever
URL: http://en.wikipedia.org/wiki/Dengue_fever
Date: October 24/2010

Author of Article: Unknown
Title of Article: Dengue and Dengue Haemorrhagic fever
URL: http://www.who.int/mediacentre/factsheets/fs117/en/index.html
Date: March 2009

Author of Article: Unknown
Title of Article: Epidemiology: Dengue Virus
URL: http://www.cdc.gov/Dengue/epidemiology/index.html
Date: July 28/2010

BY: MELODY KOTZE AND NICOLE KOREK