Dengue fever is a debilitating tropical disease caused by one of five types of the dengue virus.(1) It is transmitted by mosquitos throughout the tropics and subtropics of not only Southeast Asia, but has now spread to Central and South America, and countries in the Pacific Ocean and America as well. Usually, most people who are infected with the virus are asymptomatic, with mild symptoms, whereas others develop life threatening dengue hemorrhagic fever. The usual diagnosis of this condition is based on reported symptoms and a physical exam. Although there are still no approved vaccine or specific antiviral drug for dengue fever, many clinical developments have been implemented and a vaccine may be available in the near future.
Dengue fever is a mosquito-borne disease caused by a virus known as dengue virus. This virus continues to infect the human race and is a growing health problem in the tropic and subtropic areas, even with our current state of advanced technology and medical care. Dengue virus is from the family Flaviviridae and the genus Flavivirus. (3) It is a vector borne disease that occurs through the bite of an infected Aedes mosquito. The virus has 5 different types (DENV) 1, 2 3, 4, and 5. Once infected with the virus, symptoms include a sudden high fever, measle-like rash all over the body, headache, and muscle and joint pain. In small cases, the disease can develop into life- threatening dengue hemorrhagic fever or dengue shock syndrome. Although there are methods of prevention of this disease, the cause infecting the human body still results in many cases of this debilitating disease, probably due to urbanization increasing the habitat of aedes aegypti. (4) Currently, there is no active vaccine for this virus. However, researchers have found a candidate for a dengue vaccine that reduces the overall risk of dengue infection by 60% and may be available by late 2015. (2)
The vast history of dengue fever and aedes aegypti can date back many thousands of years ago. The earliest known records of dengue fever-like condition was found in the Chinese Medical Encyclopedia in 265-420 AD. (5) The virus aedes aegypti, spread out of Africa in the 15th to 19th centuries. There had been conveyed outbreaks of dengue fever- like symptoms since1635 in the West Indies, but it was not until 1779, when it was confirmed for the first time that dengue fever epidemic occurred in Asia, North America, and Africa almost all at once. (6) Since then, dengue epidemics have been sporadic. By 1907, it was confirmed that the Aedes mosquitos were infectious, and dengue fever was caused by a virus. (6) Outbreaks of dengue fever became more common in 1953, when an epidemic of Dengue Hemorrhagic Fever first occurred in Philippines.
Dengue fever epidemic first started out in Southeast Asia and spread into surrounding subtropical and tropical countries and continues to spread, even further out. Outbreaks in the Americas were rare due to the vector-control efforts in destroying the aedes aegypti mosquitos’ habitat. However, when they put a stop to destroying the dengue virus mosquitos in the 1970s, the mosquitoes repopulated most of the countries and by the 1990s, had expanded its habitation. Furthermore, a virus that was once thought to be confined to Southeast Asia, has had sporadic outbreaks with local transmission in the United States in the southern states such as Florida, Hawaii, and Texas. (7) Additionally, the dengue virus which had 4 types initially, now has a fifth serotype, which was discovered in 2013.
Dengue virus is a tiny virus that carries a single positive-strand of RNA as its genome within an envelope. It has about 11,000 nucleotide bases that translates ten proteins; three of these are structural proteins that form the coat of the virus and transport the RNA to target cells; and seven of them are nonstructural proteins that coordinate the production of new viruses once the virus gets inside the cell. These proteins form a protective outer layer that controls the entry of the virus into human cells.(9) Dengue fever virus belongs to the Flaviviridae family and the genus Flavivirus. There are five types of this virus, called serotypes. The first four are known as DENV -1, -2, -3, and -4. And the fifth type was discovered in 2013. Although the serotypes may differ from one another, they have similar clinical manifestations. (10)
Dengue fever virus can be transmitted in the body by a single bite from an aedes aegypti mosquito. Humans are the primary host in the virus, but it can also circulate in nonhuman primates. When an aedes aegypti mosquito bites a person, the virus penetrates into the skin along with the mosquito’s saliva. The virus binds and enters white blood cells, and replicates inside the cells. When the dengue virus is injected into the skin, the dengue virus binds onto the epidermis and dermis, which results in an infection of dendritic cells. The infected cells then move to the closest lymph node, while the dengue virus genome is translated in the endoplasmic reticulum, and replicates the viral RNA.
The mature viruses of the infected cells are released by exocytosis. They are then able to enter other white blood cells, such as monocytes and macrophages.(12) The white blood cells send out a signal, and respond by producing cytokines and interferons, which are responsible for the fever, the flu-like symptoms. Sometimes our bodies can accumulate too much of the virus, and can cause severe infection and can cause organ damage. Fluid from the bloodstream leaks into body cavities. And as a result, there isn’t enough blood to supply to vital organs. Furthermore, infection of the stromal cells leads to risk of bleeding.
Usually, most people with infected dengue virus are asymptomatic with mild fever symptoms. Some have severe illnesses, and in a small percentage, it can be fatal. The incubation period is usually 4 to 7 days, but can range from 3 to14 days. Common characteristics of dengue fever include a sudden fever, retoorbital pain, joint and muscle pain “breakbone fever” and a measle-like rash all over the body. The symptoms of dengue fever occur in 3 phases: febrile, critical, and recovery. The febrile phase includes a high fever over 104 degrees Fahrenheit, a headache, nausea, and generalized weakness that lasts 2-7 days. Also, a rash and mild bleeding in the mucous membranes.
After the fever resolves, the disease continues onto the critical phase. This phase includes leakage of plasma from the blood vessels and usually lasts for 2 days. This can lead to fluid collection of the chest and abdominal cavities as well as a high loss of fluids and reduced blood supply to vital organs. Extreme blood depletion puts one at a high risk of of developing dengue hemorrhagic fever and dengue shock. Although the critical phase is rare, it is more common in kids than adults. The recovery phase is the last phase of the dengue symptoms. Resorption of leaked fluids are returned into the blood stream. Also with symptoms of severe itching and a decreased heart rate. Fluidoverload can occur in this stage, affecting the brain, which can cause seizures and/ or a altered level of consciousness.
As dengue fever cases grow in numbers, we cannot help but wonder if and when an outbreak will occur due to the new found studies of a fifth type of aedes aegyoti virus. The mosquito-borne tropical virus, has evolved out of its origin and is continuing to spread to more countries. Dengue fever is being seen more in those who travel around the world. Although this disease is deadly, it is rare and people should fully recover from these debilitating symptoms. There is no particular treatment for this disease. Treatment depends on dengue symptoms. Currently, researchers are working on a dengue fever vaccine that can reduce the risk up to 60 percent, which is supposed to be introduced and ready in 2015.
Courtney from Study Moose
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