How The Dengue Fever Is Transmitted Biology Essay



Dengue fever is a disease caused by one of a number of viruses which are carried by mosquitoes. Then, these mosquitoes transmit the virus to humans. The virus that causes dengue fever has called an arbovirus, which is the short form for viruses transmitted by arthropods. Mosquitoes are a type of arthropod. In a number of areas, mosquitoes carry this virus and are responsible for passing it along to humans. These regions include the Middle East, Far East, Africa, the Islands Caribbean and countries of Asia such as the India, Sri Lanka and the Thailand. In these areas, Arboviruses of dengue fever is widespread, which means that the virus naturally and repeatedly and repeatedly lives at those countries.

To understand how the dengue fever is transmitted, several conditions must be defined. The word "host" means an animal or human that can be infected with a particular disease. The word "vector" means a body that can carry a particular disease causing agent such as a virus or bacteria without actually develop the disease. The vector can then pass the virus or bacteria to a new host (1).

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Most common diseases include the cold, many viral causes of diarrhea and flu or the influenza spread because the viruses that cause these diseases can be transmitted directly from one person to another. However, dengue fever cannot be transmitted directly from one person infected with another. The dengue virus must need an intermediate vector, a mosquito which carries the virus from one host to another. The mosquito that carries the Arboviruses, responsible for dengue fever is the same type of mosquitoes that can transmit other diseases such as yellow fever. This mosquito is called Aedes egypti. The most frequent victims are children less than 10 years (2).

Dengue, Viral Infection

When a person feeds by an infected mosquito, it injected dengue virus in the bloodstream. The virus infects close to skin cells called keratinocytes, the most common type in skin cells. The dengue virus has also infected and reproduced within a specialized immune cell in the skin, a dendritic cell type called a Langerhans cell.

Langerhans cells detect the pathogenic invaders and display molecules from the pathogens known as Antigen, on their surface. Langerhans cells then travel to the lymph nodes and alert the immune system to trigger immune response as a pathogen in the body. Lymph nodes are small organs located all the way through body, linked by vessels that form a network called the lymphatic system (3). Lymph nodes are stations in the body for this fight to help against infection of immune cells.

The immune response

When a pathogen as dengue virus invades the human body, the body to defend itself by defense of the body against pathogenic invaders is the immune system, which consists of two parts. The first part, called the innate immune system, provides the body with immediate and general protection of any pathogen that invading. The innate immune response quickly recognizes and responds to pathogens, but it does not provide a person with immunity in the long term against an invasion of pathogens. The second part of the immune system, the adaptive immune system produces cells that target more precisely and effectively towards pathogens and infected cells. The cells produced by the Adaptive immune system include some B cells secreting antibodies and cytotoxic t cells. Antibodies (called immunoglobulin or Ig) secreted by the cells B specially recognize and attach to foreign molecules. Cytotoxic T cells kill cells infected with pathogens. The Adaptive immune system takes longer to respond to a pathogen that invades the innate immune response (4), but it is a person with immunity against a pathogen in long-term.

How the Dengue Virus Tricks the immune system

A person is infected with the dengue virus when an infected mosquito bites the skin of the person. The dengue virus infects Langerhans cells, a type of dendritic cells in the skin. Infected cells of Langerhans produce interferons can help to limit the continued spread of the infection. Other infected cells to travel to the lymph nodes carrying viruses that infect more cells of Langerhans. Viremia is resulted by the spread of dengue virus when the high level of bloodstream affected. To fight the infection, the immune system produces antibodies to neutralize the virus particles of dengue and the complement system is enabled for antibodies and white blood cells to get rid of the virus. The immune response also includes cytotoxic T cells (lymphocytes), which identify and destroy infected cells.

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Langerhans cells once infected by dengue virus, they travel on the site of the infection of the skin to lymph nodes. The immune system responds to Infected Langerhans cells are viral antigens of dengue fever on their surface, which enables the innate immune response in alerting the two types of white blood cells called macrophages and monocytes that fight against the virus. In general, monocytes and macrophages ingest and destroy pathogens, but instead of destroying the dengue virus, the two types of white blood cells are targeted and infected by the virus. Dengue virus tricks the immune system to circumvent the defenses and infect more cells (5). As the infected monocytes and macrophages to travel through the lymphatic system, the dengue virus spreads throughout the body. Throughout his trip, the dengue virus infects more cells, including those in the lymph nodes and bone marrow macrophages of the spleen and liver and monocytes in the blood. The spread and the increase in the results of virus Viremia is a condition in which there is a high level e of dengue virus in the bloodstream.

There are four different strains of dengue virus. These strains are very similar; so similar in the fact that the immune system recognizes all after seeing one. But the recognition is not protection. T - Human cells each are programmed to recognize a specific model (or Antigen). In the first viral infection will be captured and processed by the so-called antigen presenting cells. These viruses will be presented to t cells forcing them to become activated. And even the B cells will meet their floating free Antigen and become activated. B-cells produce antibodies. Antibodies are used to tag the virus to encourage their uptake by macrophages (called opsonisation) and inactivate them.

The first infection is identified as dengue fever and lasted 6 or 7 days (6). Its symptoms closely look like severe flu. Most people get over it without incident. If one become infected again things could go wrong. There are four Dengue strains that all are very similar. If you are infected with a different strain that you met the first time, you contract dengue hemorrhagic fever.

The reason for happening this is, it turns out that the first infection antibodies attach to virus particles but not inactivate them. The strains are different enough to remain active in the presence of antibodies against another strain. These are called non neutralizing antibodies. These antibodies will always result in the opsonization. If the Macrophages are readily transmittable virus. These speeds up the course on a point infection such as hemorrhagic symptoms are observed. It is one of those interesting times where our immune system not succeeds us. If people were vaccinated dengue and if someone missed one of the four vaccines or one has been inactivated by the improper storage, they would be very susceptible to dengue hemorrhagic fever.

How the immune system Defeats the Dengue Virus

Although the dengue virus has trapped the immune system to infect cells and spread throughout the body, the immune system has additional defenses against the virus. Infected cells produce and release the small proteins called interferons that are part of a large collection of proteins called cytokines. Interferons have the ability to interfere with viral replication and they activate both innate and adaptive immune defenses. They help the immune system recognizes cells infected by dengue and help protect cells not infected infection. The immune system, fight against dengue infection so the person will experience a fever (7).

As the Adaptive immune response begins to fight against dengue infection, b cells produce antibodies IgM and IgG which are released into the blood and lymphatic fluid, where they specifically identify and deactivate dengue virus particles. In another immune response adaptation, killer T cells or cytotoxic T cells, recognize and kill cells infected with the dengue virus. Active innate immune response of the complement system, response that helps antibodies and white blood cells get rid of the virus. Together, the innate and adaptive immune responses neutralize infection of dengue, and the patient recovers dengue.

When there is a high level of virus in the bloodstream an infected person is experiencing acute dengue symptoms. As the immune response against infection by the dengue, person’s B cells begin to create antibodies called IgM and IgG which are released into the blood and lymph fluid, where they recognize and neutralize the dengue virus and the viral such as dengue NS1 protein molecules. The immune response get rid of the virus and leading to recovery.

Secondary infections of Dengue

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After a first dengue infection, a person is protected against infection with the three serotypes of dengue rest for two to three months. Unfortunately, it is not a long-term protection, and after this short time period, a person can be infected with any of the three serotypes of dengue that are remaining.

In the 1960s, Dr. Scott Halstead and his colleagues are studying in Thailand dengue virus (8). They noticed that the people who had been exposed to dengue a second time had an increased risk of severe dengue compared with those who had not been exposed previously. They were asking what makes a second infection of dengue, worse than the first.

Normally after an infection by a pathogen, the body remembers the infection for long because the cells, called memory b cells and memory t cells - remain in the body. Because they remember the first infection, memory cells can respond quickly to provide an adaptive response, when infection occurs a second time. Memory cells can remain in the body for many years, or even a lifetime. These memory cells help fight a second dengue infection. More often worse than the first infection second dengue infection.

Halstead proposes a phenomenon called "dependent improvement of antibodies to the infection" to explain these observations. There are four types of dengue (serotypes), but the cells of memory do the immunity against reinfection by serotype of dengue fever that caused the first infection. When a person is infected with a second dengue serotype, Halstead suggested that antibodies to the first infection actually help spread of dengue virus infection and increase the amount of virus in the blood, Viremia. This phenomenon can also occur in children who received antibodies against dengue of their mother while in the uterus. Curiously, rather than destroy the virus, existing antibody and the antibody newly produced by the memory can of b cells actually help the virus infected host cells more effectively. Ironically, the consequence of dependent development of antibodies is the response of the immune system in fact makes the clinical symptoms of the dengue fever situation and raises the risk of serious diseases of dengue.

In a second dengue infection cytotoxic T produced by the immune system cells provide only partial immunity against the new serotype of dengue (9). Cytotoxic T cells do not effectively clear the virus from the body, and they release the excess amounts of molecules called cytokines. In normal quantities, cytokines help the immune response. However, in large quantities, cytokines may produce severe inflammation and tissue such as capillary leak; eventually contribute to the development of serious diseases of dengue.

Factors That Contribute to Severe Dengue Infections

Prevention of dengue fever means decreasing the mosquito population. Any sources of standing water (buckets, vases, etc.) where the mosquitoes can breed must be eliminated. Mosquito repellant is recommended for those areas where dengue fever is endemic. To help break the cycle of transmission, sick patients should be placed in bed net so that mosquitoes cannot bite them and become arboviral vectors (10).

Became the prevention and the fight against dengue, dengue hemorrhagic fever and urgent distribution of geographic expansion and increase the spread of the disease over the last 20 years. Unfortunately, the tools available to prevent dengue are very limited. There is no vaccine currently available, and the limited options available to fight against mosquitoes. Clearly, the emphasis should be on prevention of the disease, and if the trend emerging diseases must be reversed.

If the effective prevention of the disease and several integrated components, including active laboratory surveillance and emergency response, and education of the medical community to ensure effective management of the situation, mosquitoes community integrated pest and use of effective vaccines when available Disease Control active is an important part of prevention program against dengue. In addition to monitoring secular trends, the purpose of monitoring should be to give warning or predictive capability for the transfer of the epidemic, and the reason is that if you cannot predict epidemics can be avoided by starting by fighting against mosquitoes emergency. For the prediction of epidemics, health authorities and should be able to precisely control the transfer of dengue virus in the community and be able to say at any time that the virus is transmitted virus serotypes rotation and related this kind of disease with dengue infection. To do this, the system must be on site and laborat

Causes and symptoms

Dengue fever can occur when a mosquito carrying the Arboviruses bites a human, passing the virus on to the new host. Once in the body, the virus travels to various Acorn where it impacted. The virus can then enter the bloodstream. The presence of the virus within the blood vessels, especially those feeding the skin, causes changes to these blood vessels. The vessels swell and leak. The spleen and lymph nodes become enlarged, and patches of liver tissue die. A process called disseminated intravascular coagulation (DIC) occurs, where chemicals responsible for clotting are used up and lead to a risk of severe bleeding (hemorrhage).

After the virus has been transmitted to the human host, occurs a period of incubation. During this time it last approximately five to eight days, the virus multiplies. The symptoms of the disease appear suddenly and include high fever, chills, headacheeye pain, red eyes, lymph nodes swollen, red hunting in the face, back pain, extreme weakness and severe pain in the legs and joints.

This initial period of the disease is about two or three days. After this time, the fever decreases rapidly, and the patient sweats strongly. After about a day to feel relatively well, the patient temperature increases again, but not as much as the first time. Begins a rash of small red bumps on arms and legs, spread to the chest, abdomen and back. It rarely affects the face. The palms of the hands and the soles of the feet swollen and turn bright red. The combination of characteristic of fever, rash and headaches are called the "dengue triad." Most people recover fully from dengue fever, although the weakness and fatigue may last several weeks. Once a person has been infected by dengue fever, his immune system guards produce cells that prevent reinfection for about a year.

More serious diseases can occur in some people. These persons may meet with dengue fever for the first time. However, in some cases, that a person may have already had dengue recovered at a time and then is re-infected with the virus. In these cases, the infection first teaches the immune system to recognize the presence of the Arboviruses. When the immune cells the virus infections later, the immune system reacts. These types of disease called dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) (11), involve more severe symptoms. Fever and headache are the first symptoms, but symptoms of dengue fever are absent. The patient develops a cough, followed by the appearance of small purple spots (petechiae) on the skin. The petechiae are areas where the blood is leaking from the ships. Large areas bruises appear as the is getting worse bleeding and abdominal pain can be severe. The patient may begin to vomit a substance that resembles coffee. It is actually a sign of bleeding in the stomach (12). As the blood vessels become more damaged, they leak more and continue to increase in diameter (dilation), causing a decrease in blood flow to the tissues of the body. This state of low blood flow is called shock. Shock can cause damage to the organs of the body especially the heart and kidneys, because the low blood flow deprived oxygen.


Diagnosis should be suspected in endemic areas each time that a high fever continues for two to seven days, especially if accompanied by a tendency to bleeding. The symptoms of shock should suggest the progression of the disease to the MAS.

Arboviruses causing dengue fever is one of the few types of Arboviruses that can be isolated from the blood serum (13). The serum is the fluid in which blood cells are suspended. Serum can be verified because the phase in which the virus moves into the bloodstream is longer in DF than in other arbovirues infections. A number of tests are used to find reactions between the serum of the patient and antibodies produced in the laboratory. Antibodies are special cells that recognize the markers or antigens present on the invasion of the agencies. During these tests, the antibodies are added to a sample of the patient serum. Health care workers and then looks for reactions that would occur only if the virus antigens are present in the serum.

New diagnostic technology

In recent years, he has developed several new methods of diagnosis and has proved very useful in the diagnosis of dengue. After reviewing this issue in depth over the past. Here follows a brief description of the various methods below.


Reverse transcriptase PCR (RT-PCR) was developed for a number of RNA viruses in recent years and has the potential to revolutionize laboratory diagnosis of dengue (14). RT-PCR provides a rapid diagnosis specific serum. This method is rapid, sensitive, simple and reproducible if handled properly, can be used to detect viral RNA in human clinical specimens and autopsy tissues, or mosquitoes. There were number of methods developed involving primers genome in different places and different methods to detect RT-PCR products in recent years.


A major problem in the laboratory diagnosis of dengue confirmation of fatal cases. only one sample is obtained serum and serological tests of limited value. In addition, most patients die at the same time or shortly after defervescence, when virus isolation is difficult. With new methods of building, it is now possible to detect antigens of dengue viruses in a variety of tissues.


There is no treatment available to shorten the course of dengue fever DHF or DSS. Drugs to reduce fever and decrease muscle pain and headache pain. Fluids are given through a needle into a vein to prevent dewatering. Blood transfusion may be necessary if serious bleeding occurs. Oxygen should be administered to patients in shock (15).


The immune system is the body's defense against viruses dengue Home. When a person is infected with the dengue response and innate and adaptive immune to join forces to fight the virus. B cells produce antibodies that specifically recognize and neutralize foreign particles and viral cytotoxic T cells to recognize and destroy cells that are infected by the dengue virus. For people who can develop later with another type of dengue virus experience called "antibody based on the promotion." This situation occurs when the immune response leads one clinical symptoms of dengue worse, which increases the risk of severe dengue.