The Assignment: Dengue Fever

Dengue is the most prevalent mosquito-borne viral illness. The viral etiology of dengue fever was established in the 1940’s and dengue-like illnesses date back over 200 years. Each year over 100 million dengue infections occur worldwide. It is said that every year 2.5 billion people are at risk for the infection.

EPIDEMIOLOGY

Dengue viruses are members of the family Flaviviridae, genus flavivirus. Four antigenically related but distinct dengue viruses exist. All dengue viruses are mosquito-borne human pathogens that cause an exclusively acute infection. The dengue viruses are maintained through the human-mosquito-human cycle and involve mosquitos of the genus Aedes. Transmission of the virus can occur between mosquitoes and nonhuman primates but no evidence exists that this is an important reservoir for transmission to humans.

Aedes aegypti mosquitoes have many characteristics that make them ideal for dissemination of the virus. A. aegypti usually breed in proximity to houses, laying eggs in water containers. A. aegypti are daytime feeders that prefer to bite humans are frequently unnoticed. They frequently take multiple blood meals in a single breeding cycle. For this reason, A. aegypti mosquitoes are able to transmit dengue virus to several individuals in a small area.

aegypti are widely distributed in tropical and subtropical areas.

TRANSMISSION PATTERNS

Epidemic dengue- this type of transmission occurs when dengue virus is introduced into a region as an isolated event involving a single virus strain. When large populations of susceptible hosts and mosquitoes are present transmission of dengue becomes explosive. In this kind of transmission the incidence of infection among susceptible individuals often reaches 25 to 50 percent.

This pattern predominated the transmission of dengue in the pre-WWII era. Initial introduction of the dengue virus frequently occurred at seaports and port cities acted as distribution points for inland areas. Epidemic transmission currently predominates virus transmission in certain parts of South America and Africa and smaller island nations. The incidence of the virus varies considerably from year to year and the risk for acquisition of the virus for travelers is high during an epidemic but low at other times.

Hyperendemic dengue- this type of transmission refers to the continuous circulation of multiple dengue virus serotypes in the same area. This type of transmission requires the year-round presence of competent vector mosquitoes and a large population base. Arease with hyperendemic dengue virus transmission contribute to the majority of cases of dengue worldwide. The overall risk for acquisition for travelers is higher in these areas.

CLINICAL PRESENTATION

The clinical manisfestation of dengue fever ranges from self-limited dengue fever to dengue hemorrhagic fever with shock. Research has indicated that all dengue virus infections are symptomatic. Age appears to be an important factor in the prevalence of symptomatic disease with children more likely to have asymptomatic disease. Symptoms typically occur between four and seven days after the bite of a mosquito although the incubation can range anywhere from 3 to 14 days. Dengue can be excluded as the cause of symptoms in a traveler developing illness more than 14 days after returning from a dengue-endemic region.

Classic Dengue: Classically dengue fever presents as an acute febrile illness with headache, retroorbital pain, and marked muscle and joint pain. The severe muscle and joint pain has cause dengue fever to be called “break bone fever”. The fever component of the illness typically lasts for 5 to 7 days. The febrile period can be followed by a period of marked fatigue that can last for days to weeks. Physical exam is usually non-specific but may include macular or maculopapular rash.

Hemorrhagic Dengue: Hemorrhagic manifestations are common in patients with dengue fever and are rarely life-threatening. Hemorrhagic manifestations include petechiae, ecchymoses, purpura, hematemesis, metrorrhagia, melena, and spontaneous bleeding. The risk of severe disease is higher in sequential dengue infection. The four cardinal features of Dengue hemorrhagic fever include increased vascular permeability, fever, hemorrhage, and marked thrombocytopenia

DIAGNOSIS

The diagnosis of acute dengue virus infection is primarily clinical. Often patients with dengue fever have a positive tourniquet test, leucopenia, thrombocytopenia, and increased AST level in comparison to patient’s with other febrile illnesses. In developing countries, dengue hemorrhagic fever is frequently diagnoses based upon classification established by the World Health Organization. When dengue virus infection is clinically suspected the patient is treated empirically.

Confirmation of acute dengue virus infection is most frequently accomplished with serology. The most frequently used serologic tests for the diagnosis of acute dengue virus infection are the hemagglutination inhibition (HI) assay and IgG or IgM enzyme immunoassays.

TREATMENT

There is no specific treatment available for Dengue fever therefore it is important to exclude other treatable causes. Other disease that present like dengue include malaria, thyphoid fever, and leptospirosis. Supportive treatments are available for the manifestations of dengue fever. Patients should be maintain their intake of fluids to prevent dehydration. Fever and myalgias can be managed with acetaminophen and aspirin and NSAIDs should be avoided because of the risk of bleeding complications. Most importantly patients should be carefully monitored for signs of complications. The period of maximum risk for shock is between the third and seventh day of illness near defervescence. Plasma leakage usually occurs during this period. Red Flags include severe abdominal pain, persistent vomiting, altered mental status. Other signs include elevation of hematocrit, severe thrombocytopenia, increased AST, and hypotension.

PREVENTION

The greatest risk for dengue virus infection is in individuals living in endemic areas not in travelers. Mosquito control is the most effective approach to prevention of transmission. A vaccine against all 4 serotypes does not yet exist, but it is currently in development.

http://www.cdc.gov/NCIDOD/DVBID/dengue/