Dengue, a mosquito-borne infection, has become a serious worldwide health concern in recent years. Pronounced “DENG-ghee,” it’s found primarily in tropical and sub-tropical regions; but unlike malaria, it clusters in urban and semi-urban areas. A potentially fatal complication of dengue called dengue hemorrhagic fever, or DHF, was first reported in Thailand and the Philippines in the 1950s. Since then DHF has migrated to affect most Asian countries. DHF is a leading cause of hospitalization and death among children in several of those nations. Scientists believe dengue hemorrhagic fever occurs when a victim who has previously suffered from dengue infection acquires yet another viral strain of the disease. The most common victims of DHF are Caucasian girls younger than twelve years.
DHF, sometimes called dengue shock syndrome or Philippines/Singapore/Thai hemorrhagic fever, is endemic in over a hundred countries. It has been reported in the Eastern Mediterranean, Southeast Asia, the western Pacific, the Americas, and Africa. Of these, Southeast Asia and the western Pacific are the most severely affected. Until 1970, only nine countries had suffered epidemics of dengue fever. By 1995, that number had climbed to almost forty. Some forty percent of the world’s population, or 2.5 billion people, are at risk of dengue infection. The World Health Organization (WHO) believes as many as fifty million people suffer from the disease each year. Even in the Americas, over six hundred thousand people reported dengue infection in 2001. Only half that many cases were recorded only six years earlier.
Dengue mortality estimates vary from two to five percent. Those values climb by twenty percent in the absence of adequate medical structures.
The disease is caused by one of four closely related arboviruses. If a patient recovers from infection by one of the viruses, he or she is only partially protected against infection by any of the other three. WHO scientists believe infections tend to increase in severity after first acquisition. The viruses are transmitted to humans from the bite of infected mosquitoes in the order Aedes. These mosquitoes acquire the disease by biting an infected person. Eight to ten days later, the virus enters the mosquito’s saliva, where it can be injected into another person during a blood meal. The virus circulates in human beings for two to seven days and may then be passed into yet another mosquito. Urban areas have experienced a rapid increase in Aedes aegypti mosquito populations, a species which can and does transmit all four dengue viruses.
Recent studies indicate monkeys can also act as a host for the virus, and they may be the source of some dengue infections in mosquitoes. Scientists believe infected mosquito females can transmit the virus to their eggs (i.e., transovarially), thus giving birth to whole clutches of infected mosquitoes.