A neglected disease

Machteld Julsing

 

 

History

There are four types of the dengue virus: DENV-1, -2, -3 and -4. They all belong to the family of the Flaviviridae. The virus is transmitted by the Aedes aegypti mosquito.

Aedes aegypti probably has its origin in Egypt. It crossed the Atlantic Ocean from Africa in times of slavery. The name dengue is a derived from the Swahili sentence ki denga pepo, which means it is a sudden overtaking by an evil spirit. It refers to the rapid onset of the disease. This appeared in English literature during a Caribbean outbreak in 1827-28. The first definite clinical report of dengue is attributed to Benjamin Rush in 1789, but the viral aetiology and its mode of transmission via mosquitoes were not established until early 20th century.

Epidemiology

Two hundred years ago, dengue only sporadically caused an epidemic. It spread from South-East Asia to America, the Pacific Ocean, Africa and the Carribbean. The reason for the spread is the increasing possibilities for travelling. Nowadays dengue is the most important mosquito-transmitted viral disease worldwide. In comparison to five decades ago, the recent incidence multiplied thirtyfold; a very disturbing evaluation. More countries are infected and also the epidemics are massively explosive. For instance in 2007 there was an outbreak in Venezuela, reporting 80 000 cases of dengue, including over 6 000 cases of DHF.

Pathophysiology

Frequently, dengue viral infections are asymptomatic. Symptomatic dengue predominantly occurs in the immunocompromised or non-indigenous. The symptoms include fever, rash, pain in muscles and joints and start abruptly with minor illness for two to four days followed by rapid worsening, after an incubation period of five to ten days. 

Being infected with one serotype gives a lifelong immunity against that serotype, but merely a small and passing protection against the other ones. A small percentage of patients who have previously been infected by one dengue serotype develop bleeding and endothelial leak upon infection with another dengue serotype. This syndrome is termed dengue haemorrhagic fever (DHF) which can result in dengue shock syndrome (DSS) and may cause death. 

Transmission

Dengue fever is transmitted from human to human or from primate to human by the female Aedes aegypti mosquito. The mosquito lays her eggs in standing water in garbage dumps in inner cities. Clothing provides no protection against Aedes aegypti that bites during daytime, as opposed to the malaria mosquito. The virus circulates in the patient’s blood for two to seven days.

Diagnosis

First dengue infection can be diagnosed by the IgM-capture Enzyme-Linked ImmunoSorbant Assay (ELISA). For second infection other serological diagnostic tests are needed as research shows that 28% of the second infections were missed by ELISA. For DHF the blood pressure tourniquet test is used. The test is DHF positive when more than 20 petechiae per square inch appear.

Treatment

Dengue fever is self-limiting and therefore treatment is only needed to reduce symptoms. DHF and DSS are a different story. Patients should be admitted right away. Administration of oxygen, hydration with intravenous sodium solution and treatment against DIC can be life saving.

Prevention

Until today there is no dengue vaccine but research is in progress. Education can inform people about standing water as the source of mosquito multiplication and about how vinegar might be used to destroy the eggs and larvae of the Aedes aegypti.

Further reading

• WHO. Dengue Haemorrhagic Fever: early recognition, diagnosis and hospital management. 2006 via http://www.who.int/csr/disease/dengue/en/index.html
• Harrison's principles of Internal Medicine

References