Dengue Fever Causes Symptoms and Treatment

Dengue fever is a debilitating infectious disease caused by the dengue virus and transmitted by mosquitoes. It is characterized by the dengue triad, high fever, rashes, and intense headache, body ache, and joint aches. It is also called the "break-bone fever" because it causes severe body and joint aches and pains. The disease is found throughout the world and more prevalent in the tropics and the subtropics where the climate is especially hot and rainy. It is common in South and Southeast Asia, Northern Australia, SubSaharan Africa, Central and South America, parts of Caribbean etc. The disease occurs at the start of the rainy season and immediately after it. ​​The dengue virus has 4 different types, types 1, 2, 3, and 4. Infection with any one type gives lifelong immunity to that type of virus but only short term immunity to the other types. The mortality rate is 3 to 30 in every 100 cases.

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​Signs and symptoms

The characteristic symptoms of dengue include sudden-onset fever, headaches typically located behind the eyes, muscle and joint pains, swollen glands, and a characteristic rash that is similar to measles. The incubation period of dengue fever ranges from 3-14 days. Most people, 80%, who are infected with the dengue virus are asymptomatic. The other 5% have more severe symptoms, and for the rest it is life threatening.

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​Transmission and Clinical Course

The dengue virus is transmitted by the Aedes mosquitoes and more specifically by the genus Aedes eagypti. The other Aedes mosquito species that spread dengue include A. albopictus, A. polynesiensis, and A. scutellaris. These mosquitoes bite during the day and the infection can be acquired with a single bite. Female mosquitoes are those which causes the disease. Humans are the primary host of the disease. Dengue virus is present in the blood of an infected person suffering from the dengue fever. The female mosquito sucks the blood from the person suffering from dengue fever, and the mosquito themselves get infected with the virus in the cells lining the gut. The virus spreads to other tissues of the mosquito which involves the salivary glands and it is therefore is released into the saliva. In fact, the mosquito does not get any adverse effects of the disease while it is being infected and the virus stays in the mosquito for life. These mosquitoes prefer to lay their eggs in stagnant water near human dwelling and feed on the blood of human rather than on other vertebrates.

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When a mosquito that carries the dengue virus bites a person, the virus enters the skin along with the saliva of the mosquito. It enters the blood and binds with the white blood cells and reproduces inside it while they move throughout the body. The white blood cells responds by producing several proteins such as interferon and these proteins produces many symptoms such as fever, flu-like symptoms, severe pains and aches. In severe infection, the reproduction of the virus is greater and many organs and organ systems are affected such as the liver, bone marrow etc. The fluid and plasma from the blood leaks through the walls of the blood vessel into the body cavities. Due to this, there will be less blood that will circulate through the blood vessels and the blood pressure drops to low. Because there is less blood that is present in the blood vessels it cannot supply sufficient oxygen or nutrients to the the vital organs, thus producing serious effects. When the bone marrow is affected, it causes dysfunction that leads to reduced number of platelets resulting in decreased clotting of blood. Decreased clotting of blood leads to increased risk of bleeding mostly through soft mucous membranes, which is a serious complication.

Dengue can also be transmitted through blood transfusion, blood products and organ transplants. Vertical transmission from mother to the child does occur. Some rare person to person mode of transmission also occur.

​Predisposition

The severe effects of the dengue fever are seen mostly in children and babies. It is more common in children who are well nourished. It also affects women more than men. Dengue fever is a life threatening disease in people who have chronic diseases such as diabetes, asthma, clotting disorders etc.

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​Phases of Infection

There are 3 phases of infection, and they are febrile phase, critical phase, and recovery phase.

The febrile phase involves high fever often above 40 degree centigrade associated with generalized aches and pains and headache, which lasts for 2 to 7 days. A rash occurs in 50%-80% of those with symptoms. It occurs as a flushed-skin type to a measles-type rash. Some petechiae or red raised spots with bleeding are noted on the skin and there may be mild bleeding from the mucous membranes of the mouth and nose. The fever often fluctuates by breaking and then returning in 1 or 2 days.

The disease sometimes proceed to a critical phase in some people that follows the resolution of the fever and it lasts for 1 to 2 days. There is significant amount of fluid accumulation in the chest and abdominal cavity due to increased permeability and leakage. It leads to depletion of fluid from the blood vessels and decreased blood flow to the vital organs. Multiple organ dysfunction, abdominal pain and severe bleeding from the gastrointestinal tract may occur. Shock often known as dengue shock and the hemorrhage known as dengue hemorrhagic fever occur in less than 5% of the cases. Dengue hemorrhagic fever is a life threatening condition where there is low levels of blood platelets and bleeding and blood plasma leakage. It leads to the dengue shock syndrome characterized by extremely low blood pressure.Those previously infected with other types of dengue virus are at an increased risk.

The recovery phase is characterized by resorption of the leaked fluid into the blood stream and it can last about 2 to 3 days. There may be severe itching and slow heart rate. A severe fluid overload state may occur that affects various organs. When it affects the brain there will be reduced level of consciousness and seizures. Other dengue complications include neurological disorders like  transverse myelitis and Guillain-Barre syndrome and infections occur such as infection of the heart and acute liver failure.

Diagnosis

The diagnosis dengue is made clinically based on the reported symptoms and physical examination that includes fever, nausea and vomiting, rash, generalized pains, low white blood cell count, positive tourniquet test, or any warning signs such as abdominal pain, ongoing vomiting, liver enlargement, mucosal bleeding, high hematocrit count with low platelets, lethargy in someone who lives in an endemic area.

Laboratory Tests

Dengue fever can be diagnosed with laboratory testing methods done by virus isolation in cell cultures, nucleic acid detection by PCR, viral antigen detection, or specific antibodies.

Management

There are no specific treatments or vaccines for dengue fever. Treatment of dengue fever depends on the symptoms and their management, which includes oral rehydration therapy, close follow up, hospital admission with administration of intravenous fluids, blood transfusion etc. ​Invasive medical procedures such as nasogastric intubation or intramuscular injections are avoided to prevent any bleeding complications. Drugs such as paracetamol is used for fever and discomfort. NSAIDs such as ibuprofen and aspirin are avoided to prevent any risk of bleeding. Blood transfusion is given for patients presenting with unstable vital signs or decreasing hematocrit. Packed red blood cells or whole blood is given for severely hypovolemic patients. Platelets or fresh frozen plasma are usually not given.

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Prevention

There are no vaccines for dengue virus. Prevention of dengue virus is through the control of mosquitoes and avoiding mosquito bites.

The primary method of controlling Aedes eagypti is by eliminating its habitats. This is through various means such as:

Emptying water where it is collected such as containers or collectors either natural or artificial.

Adding insecticides or biological pest control agents in those water bodies.

Environmental modification or reduction of open collections of water.

Closing any air holes of septic tanks and other drainage pipes.

Draining of any stagnant water.

Wearing clothing to prevent mosquito bites such as clothing that fully covers the skin.

Using mosquito net closure on all doors, windows, ventilators, and other air channels at home.

Using mosquito net over the bed while sleeping.

Application of insect repellant on the skin.

Use of mosquito repellant smoking coil to deter mosquitoes.

Using mosquito electric bats and wire meshes to trap and kill mosquitoes.​

These are some of the methods that helps to control mosquitoes and mosquito bites and thus effectively preventing the spread of dengue fever.

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