Dengue does not have a very high mortality rate, with approximately 40 deaths per 100,000 cases recorded (0.04%). Mortality occurs almost exclusively in cases of severe dengue, also called dengue hemorrhagic fever, which is a form of dengue that leads to complications such as circulatory shock, gastrointestinal bleeding and damage to the vital organs such as liver, heart and central nervous system. Unlike simple dengue which has low mortality rate of DHF in the number of deaths is greater than 10% of cases.
Early identification of potentially serious cases it is essential that treatment be started as soon as possible, which can reduce severe dengue mortality rate to less than 1%.
In this article we will focus only on the symptoms of dengue and its laboratory findings with emphasis on the differences between simple cases and severe cases of dengue (classic dengue and hemorrhagic dengue).
The clinical status of dengue can vary from virtually asymptomatic cases to catastrophic situations, with bleeding and multiple organ failure. DHF can occur with any of the existing four serotypes of dengue virus (DEN-1, DEN-2, DEN-3 and DEN-4). In fact, it usually arises when a previously infected patient for some serotype contract the disease again, this time with a new serotype. It is believed that the severe forms of dengue occur by a heightened response of our immune system to the second infection. Therefore, patients who have had dengue at some point in their lives and have their second infection are those that should be observed more closely.
Dengue without symptoms
About 15% of people infected with dengue virus do not develop symptoms, or are so mildly that not even suspect they have the disease. The asymptomatic form of dengue fever is more common in adolescents and schoolchildren. A study in over 2,000 schools in Thailand in 2002 showed that about 53% of children who become infected with the dengue virus do not develop febrile illness in a relevant way.
It is not clear that this group develops the first infection of asymptomatic dengue presents less risk of progressing to severe forms should it become contaminated in the future with a new serotype of the virus. The fact is that the DHF board is also more common in younger patients, which shows that this group is more likely to develop milder forms and more severe dengue.
In patients who develop clinical symptoms, the disease usually have two forms of presentation: dengue fever and severe dengue (DHF).
Dengue fever
The so-called classic dengue or dengue without gravity is the most common form of presentation of this virus.
The incubation period of dengue, ie the time interval between the bite of the mosquito Aedes aegypti infected by the virus and the appearance of the first symptoms of the disease, may range from 3 to 15 days. In most cases, however, the first signs of the disease appear between 4 to 7 days.
The first manifestation of dengue is usually a high fever, around 39-40°C, which arises from sudden way. A headache, retro-orbital pain (pain behind the eyes), muscle pain, joint pain, loss of appetite, weakness, tiredness, red spots on the skin, nausea and vomiting are symptoms that usually come after them. Pain in the body usually so strong that dengue is also known as the "break-bone fever."
The patient with dengue will not necessarily have all the symptoms listed above, but most of them usually present. High fever associated with malaise, headache and body aches is most common form of presentation, occurring in about 80% of cases.
Dengue fever can also cause symptoms common to other respiratory viruses, including sore throat, cough or stuffy nose. One third of patients may have a clinical picture very similar to a stronger flu, which can make diagnosis difficult. Diarrhea is not very common, but can also occur. Soft stools, on the other hand, are frequent, affecting almost half of the patients.
The high fever lasts 3-7 days and when she begins to fall, the other symptoms also usually disappear. A weary frame, however, may still persist for some weeks after the resolution of symptoms. Some patients have a bimodal pattern of fever, or after the fever disappears, it returns suddenly for 2 days, and then disappear only once.
Dengue rash
The dengue rash is a sign that occurs in more than half of patients, usually after the 3rd day of fever. The skin patches are typically reddish, flat and spread over the trunk and limbs. The spots may coalesce, forming similar images with geographical maps, as can be seen in the next photo.
One of rash characteristics is that it evanesce momentarily when you press the skin with your fingers. The dengue spots do not usually cause itching, but some patients report some degree of itching.
The rash lasts for around 3 days and disappears without flake or stain the skin.
Hemorrhagic manifestations of classic dengue
Some authors have preferred the distinction between severe dengue x not severe dengue, rather than classical x DHF dengue. This preference makes sense because not all dengue presenting bleeding events is necessarily hemorrhagic dengue. Nosebleeds, gums, skin and feces may occur even in the so-called classical dengue. As we shall see, what characterizes dengue hemorrhagic fever (severe dengue) is not necessarily the presence of bleeding. Not all patients with bleeding are the most severe form of dengue.
The severe dengue or dengue hemorrhagic fever is an unfavorable evolution of a dengue frame. Initially, the clinical picture is exactly the same, it is not possible to distinguish those who will develop favorably or unfavorably. Complications of dengue hemorrhagic fever usually appear between 3 and 7 days of illness, usually at the same time that the fever usually improve. In the classic dengue fever, the fever subsides indicates that the disease is low. In the hemorrhagic dengue fever in the final usually marks the beginning of complications.
It is for this reason that development of dengue can be divided into febrile phase (common to severe forms and not severe dengue), critical phase (time that dengue complications arise) and recovery phase, which is when the heals disease.
As mentioned above, despite the DHF name, which defines the existence of severe dengue is not the presence of bleeding events, but rather the occurrence of what is called the plasma leakage syndrome.
Syndrome plasma extravasation
It is believed that dengue hemorrhagic fever (severe dengue) occurs not by direct action of the dengue virus, but by a heightened response of our immune system, which ultimately creates an inflammatory response throughout the most intense form of body than needed to fight the invading virus.
One of the more serious consequences is endothelial dysfunction, which is a modification of cells lining blood vessels, causing them become more permeable to water. The increase in permeability that occurs primarily in the capillaries (very small caliber vessels), there causes plasma extravasation from the blood into the tissues around it. Plasma is the portion of the blood that does not contain cells. It is primarily water, proteins and minerals.
When the plasma extravasation is relevant, a large amount of water flows out of blood vessels and is deposited in the organs and tissues. This fact raises two serious consequences: the first is a large reduction in effective circulating blood volume, which may cause the patient to what we call circulatory shock. The second consequence is the mobilization of large volumes of water to the lung, occupying the space that should be reserved for the absorption of oxygen. The end result is a respiratory failure, as if the patient were drowning.
Another place where water tends to accumulate is the abdominal cavity, causing a frame called ascites.
The degree of plasma leakage is who defines the severity of dengue. If the frame is mild, the patient often goes well for this phase. On the other hand, endothelial dysfunction is severe, the patient can progress to death in just 24 hours.
The plasma extravasation is the defining event of severe dengue. However, bleeding events are much more common in severe dengue than in dengue fever, which is why this most severe form of dengue hemorrhagic fever is also called.
As mentioned above, by the end of the febrile phase, patients with severe dengue and dengue fever have roughly the same spectrum of signs and symptoms. It is only in the critical stage we can identify who will develop well and who is at risk for complications.
While the patient with dengue fever improved with the end of fever, the patient with the most severe forms begins to show the first signs that something is not going well. Severe abdominal pain, persistent vomiting, drop in blood pressure, drowsiness, disorientation, difficulty breathing, pale and cold skin, decreased urine volume and spontaneous bleeding, especially the gastrointestinal tract, are warning signs.
In the most severe stage, many organs can be affected directly, such as heart, liver and central nervous system.
Once the plasma extravasation has begun to occur intensively, the picture evolve very quickly. Severe dengue have to be recognized immediately as the replacement of intravenous fluids must be initiated as soon as possible to prevent the patient from developing into the circulatory shock.
The critical phase lasts only 24 to 48 hours. After this period, the extravasated plasma begins to slowly be resorbed into the bloodstream, causing the patient improves progressively over the next 72 hours.
The clinical picture consisting of the signs and symptoms, laboratory findings are also very important in the investigation of dengue, whether classic or hemorrhagic.
The CBC is the most useful laboratory test. In the febrile phase, the most common finding is leukopenia, which is a drop in the number of leukocytes, a major cell defense of our blood. Another typical laboratory abnormality is thrombocytopenia, which is a drop in the number of platelets, the cells responsible for initiating the blood clotting process.
In general, dengue fever in the number of platelets is reduced, but does not fall below 100,000 cells per m3. In the hemorrhagic fever, thrombocytopenia is usually more severe, often below 50,000 cells per m3. Importantly, only the value of platelets is not sufficient to distinguish a classic dengue hemorrhagic form.
As in severe dengue there is great leakage of liquids out of the blood, the final result is an increased concentration of the cells remain there. As the red blood cells are the most abundant cells in the blood, a sudden increase in blood levels is a very strong signal that the blood is losing water quickly. Therefore, an increase of at least 20% hematocrit value tends to occur hours before the patient begins to show signs of circulatory shock.
