Dengue

Definition

Dengue fever is a disease caused by one of a number of viruses that are carried by mosquitoes. These mosquitoes then transmit the virus to humans.

Description

The virus that causes dengue fever is called an arbovirus, which stands for arthropod-borne virus. Mosquitoes are a type of arthropod. In a number of regions, mosquitoes carry this virus and are responsible for passing it along to humans. These regions include the Middle East, the far East, Africa, and the Caribbean Islands. In these locations, the dengue fever arbovirus is endemic, meaning that the virus naturally and consistently lives in that location. The disease only shows up in the United States sporadically.

In order to understand how dengue fever is transmitted, several terms need to be defined. The word "host" means an animal (including a human) that can be infected with a particular disease. The word "vector" means an organism that can carry a particular disease-causing agent (like a virus or bacteria) without actually developing the disease. The vector can then pass the virus or bacteria on to a new host.

Dengue fever cannot be passed directly from one infected person to another. Instead, the virus responsible for dengue fever requires an intermediate vector, a mosquito, that carries the virus from one host to another. The mosquito that carries the arbovirus responsible for dengue fever is the same type of mosquito that can transmit other diseases, including yellow fever. This mosquito is called Aedes egypti. The most common victims are children younger than 10 years of age.

Signs and symptoms

The disease manifests as a sudden onset of severe headache, muscle and joint pains (myalgias and arthralgias—severe pain that gives it the nickname break-bone fever or bonecrusher disease), fever, and rash. The dengue rash is characteristically bright red petechiae and usually appears first on the lower limbs and the chest; in some patients, it spreads to cover most of the body. There may also be gastritis with some combination of associated abdominal pain, nausea, vomiting, or diarrhea.

Some cases develop much milder symptoms which can be misdiagnosed as influenza or other viral infection when no rash is present. Thus travelers from tropical areas may pass on dengue inadvertently, having not been properly diagnosed at the height of their illness. Patients with dengue can pass on the infection only through mosquitoes or blood products and only while they are still febrile. The classic dengue fever lasts about two to seven days, with a smaller peak of fever at the trailing end of the disease (the so-called "biphasic pattern"). Clinically, the platelet count will drop until the patient's temperature is normal. Cases of DHF also show higher fever, variable hemorrhagic phenomena, thrombocytopenia, and hemoconcentration. A small proportion of cases lead to dengue shock syndrome (DSS) which has a high mortality rate. DHF combined with a cirrhotic liver has been suspected in rapid development of hepatocellular carcinoma (HCC). Given that the dengue virus (DEN) is related to the Hepatitis C virus, this is an avenue for further research as HCC is among the top five cancerous causes of death outside Europe and North America. Normally HCC does not occur in a cirrhotic liver for ten or more years after the cessation of the poisoning agent. DHF patients can develop HCC within one year of cessation of poisoning agent.

Diagnosis

The diagnosis of dengue is usually made clinically. The classic picture is high fever with no localising source of infection, a petechial rash with thrombocytopenia and relative leukopenia - low platelet and white blood cell count. Care has to be taken as diagnosis of DHF can mask end stage liver disease and vice versa.

Fever, bladder problem, constant headaches, eye pain, severe dizziness and loss of appetite.
Hemorrhagic tendency (positive tourniquet test, spontaneous bruising, bleeding from mucosa, gingiva, injection sites, etc.; vomiting blood, or bloody diarrhea)
Thrombocytopenia(<100,000>
Evidence of plasma leakage (hematocrit more than 20% higher than expected, or drop in hematocrit of 20% or more from baseline following IV fluid, pleural effusion, ascites hypoproteinemia)
Encephalitic occurrence

Dengue shock syndrome is defined as dengue hemorrhagic fever plus:

Weak rapid pulse,
Narrow pulse pressure (less than 20 mm Hg)
Cold, clammy skin and restlessness.

Dependable, immediate diagnosis of dengue can be performed in rural areas by the use of Rapid Diagnostic Test kits, which also differentiate between primary and secondary dengue infections.Serology and polymerase chain reaction (PCR) studies are available to confirm the diagnosis of dengue if clinically indicated. Dengue can be a life threatening fever.