Dengue tidbits

Up to 100 million cases of dengue fever—up to 500,000 of which progress to dengue hemorrhagic fever (DHF)—occur worldwide each year. Travelers should take note that dengue fever epidemics have recently been reported in Mexico and Brazil. I noticed in the news this morning that the Mexican state of Quintana Roo (map) is experiencing a growing epidemic of dengue fever and dengue hemorrhagic fever (DHF). The situation has been described as “critical” and growing. 125 patients have been recently diagnosed with dengue, 21 of them hemorrhagic.

Dengue is a concern in the southern U.S., as well. The virus is transmitted by mosquitoes of the genus Aedes; while Aedes albopictus mosquitoes are established in large areas of the U.S., dengue is still primarily found in Aedes aegypti, which is not (yet) prevalent in the U.S. In 1987, however, the CDC noted:

…confirmed dengue cases were reported in areas where Ae. aegypti and Ae. albopictus, two efficient vectors of dengue, occur. The recent introduction of Ae. albopictus into the United States is of special concern because this species is an exceptionally efficient host for dengue viruses and is capable of transmitting both horizontally (human to human) and vertically (from infected female to her offspring). Moreover, Ae. albopictus has become established in northern as well as southern states. The presence of this species increases the potential for more widely distributed secondary transmission and for the maintenance of dengue viruses in the United States.

We may see dengue expanding into the U.S. in the future, but cases among U.S. citizens today are still usually contracted during travel; however, in 2005 an outbreak of dengue occurred in Brownsville, Texas that included the first case of DHF contracted within the U.S.

While temperature, seasonal rains, and relative humidity are environmental factors affecting mosquito populations, mosquito eradication efforts around cities, towns, and individual dwellings are the key to keeping dengue in check. Along with government spraying and treatment efforts in wetlands, streams, and other natural waters, it is critical for individual citizens to deny mosquitos their habitat, i.e, securing bulk water storage containers, and removing standing water from old tires or other objects. Otherwise dengue spreads as the mosquitoes spread. More information about dengue along the southern border: MSWord or Powerpoint.

South and Southeast Asia had a large number of dengue cases during seasonal outbreaks in 2006. Malaysia reported around 12,000 cases. About 10,000 more occurred in India, with hundreds more in Pakistan where Den-3 was found to be the main cause. Den-1 and Den-4 were also found. A large number of patients in Pakistan, however, were found to have chikungunya virus, which can present similar symptoms to DHF and is also transmitted by mosquitoes of the genus Aedes. A few in Karachi were infected with both.

There is currently no licensed vaccine for dengue fever, but several programs are in progress. A short backgrounder on dengue vaccine issues can be seen here.

Background

Dengue fever results from infection of any of four serotypes of the dengue virus. Second infection with a different serotype, after once having survived dengue, can result in DHF. Den-2 and Den-3 may have a particularly bad effect on those who have previously survived dengue fever caused by Den-1. Immunity to one serotype (due to previous infection) does not confer immunity to the other 3.

On DHF, from the CDC:

Dengue hemorrhagic fever is a potentially deadly complication that is characterized by high fever, hemorrhagic phenomena—often with enlargement of the liver—and in severe cases, circulatory failure. The illness commonly begins with a sudden rise in temperature accompanied by facial flush and other non-specific constitutional symptoms of dengue fever. The fever usually continues for 2 to 7 days and can be as high as 40-41 C (104-105.8 F), possibly with febrile convulsions and hemorrhagic phenomena. In moderate DHF cases, all signs and symptoms abate after the fever subsides. In severe cases, the patient’s condition may suddenly deteriorate after a few days of fever; the temperature drops, followed by signs of circulatory failure, and the patient may rapidly go into a critical state of shock and die within 12-24 hours or quickly recover following appropriate volume replacement therapy. There is no specific treatment for dengue fever. However, careful clinical management by experienced physicians and nurses frequently saves the lives of DHF patients. With appropriate intensive supportive therapy, mortality may be reduced to less than one percent. Maintenance of the circulating fluid volume is the central feature of DHF case management.