Dengue (den-gee) also (DENG-gay) is a disease that is endemic in most of the world including at least 100 countries in Asia, the Pacific, the Americas, Africa, and the Caribbean. The World Health Organization (WHO) estimates that 50 to 100 million infections occur yearly, including 500,000 of the more severe dengue hemorraghic fever (DHF) cases and 22,000 deaths, mostly among children.
Origin: The four dengue viruses (DENV 1, DENV 2, DENV 3, or DENV 4) originated in monkeys and independently jumped to humans in Africa or Southeast Asia between 100 and 800 years ago. Dengue remained a relatively minor, geographically restricted disease until the middle of the 20th century. The disruption of the second world war – in particular the coincidental transport of Aedes mosquitoes around the world in cargo – are thought to have played a crucial role in the dissemination of the viruses. DHF was first documented only in the 1950s during epidemics in the Philippines and Thailand. It was not until 1981 that large numbers of DHF cases began to appear in the Carribean and Latin America.
Most dengue cases in U.S. citizens occur in those inhabitants of Puerto Rico, the U.S. Virgin Islands, Samoa and Guam, which are endemic for the virus. Dengue and DHF have been a particular challenge in Puerto Rico where outbreaks have been reported since 1915 and large island-wide epidemics have been documented since the late 1960s. The most recent island-wide epidemic occurred in 2007, when more than 10,000 cases were diagnosed. In Puerto Rico, and most of the Caribbean Basin, the principle dengue vectors are abundant year-round. Dengue transmission in the Puerto Rico follows a seasonal pattern. Low transmission season begins in March and lasts until June, and high transmission begins in August until November. (See CDC maps below.)
Symptoms: The principal symptoms of dengue fever (DF) are high fever, severe headache, severe pain behind the eyes, joint pain, muscle and bone pain, rash, and mild bleeding (e.g., nose or gums bleed, easy bruising). Generally, younger children and those with their first dengue infection have a milder illness than older children and adults.
Dengue hemorrhagic fever (DHF) is characterized by a fever that lasts from 2 to 7 days, with general signs and symptoms consistent with dengue fever. When the fever declines, symptoms including persistent vomiting, severe abdominal pain, and difficulty breathing, may develop. This marks the beginning of a 24- to 48-hour period when the smallest blood vessels (capillaries) become excessively permeable (“leaky”), allowing the fluid component to escape from the blood vessels into the peritoneum (causing ascites) and pleural cavity (leading to pleural effusions). This may lead to failure of the circulatory system and shock, followed by death, if circulatory failure is not corrected. In addition, the patient with DHF has a low platelet count and hemorrhagic manifestations, tendency to bruise easily or other types of skin hemorrhages, bleeding nose or gums, and possibly internal bleeding.
Transmission: Dengue is transmitted between people by the mosquitoes Aedes aegypti and Aedes albopictus, which are found throughout the world.
Incubation: Symptoms of infection usually begin 4 – 7 days after the mosquito bite and typically last 3 – 10 days. In order for transmission to occur the mosquito must feed on a person during a 5- day period when large amounts of virus are in the blood; this period usually begins a little before the person become symptomatic. Some people never have significant symptoms but can still infect mosquitoes. After entering the mosquito in the blood meal, the virus will require an additional 8-12 days incubation before it can then be transmitted to another human. The mosquito remains infected for the remainder of its life, which might be days or a few weeks.
In rare cases dengue can be transmitted in organ transplants or blood transfusions from infected donors, and there is evidence of transmission from an infected pregnant mother to her fetus. But in the vast majority of infections, a mosquito bite is responsible.
Treatment: There is no specific medication for treatment of a dengue infection. Persons who think they have dengue should use analgesics (pain relievers) with acetaminophen and avoid those containing aspirin. They should also rest, drink plenty of fluids, and consult a physician. If they feel worse (e.g., develop vomiting and severe abdominal pain) in the first 24 hours after the fever declines, they should go immediately to the hospital for evaluation.
Prevention: There is no vaccine for preventing dengue. The best preventive measure is to eliminate the places where the mosquito lays her eggs, primarily artificial containers that hold water. And proper application of mosquito repellents containing 20% to 30% DEET as the active ingredient on exposed skin and clothing decreases the risk of being bitten by mosquitoes.