Dengue Fever What You Should Know

The Philippines being a tropical country hosts a myriad of diseases. We hear of Dengue fever and Dengue hemorrhagic fever on a yearly basis. Although it is already past the peak season of Dengue illness, it pays to know more about this disease. There are still sporadic cases all year long.

The causative agent of Dengue is a Flavivirus. The virus belongs to the group that shares a common feature, they are arthropod-borne hence the group name arbovirus or arboviridae. For Dengue disease, the vector is a mosquito. In the Philippines it is the Aedes aegypti mosquito. This is a day-biting mosquito that thrives in urban communities. There are two interconnected cycles, the sylvan and urban cycles. The sylvan cycle maintains the existence of the virus in the wild. The flavivirus is transmitted between the Aedes vector and a mammal host. The urban cycle starts when a carrier mosquito happens to wander to an urban community. A human host will be infected through mosquito bites. The infected blood will then be spread to other susceptible hosts by the Aedes vector. The mosquito is infective from the second week after biting a viremic human and remains so for several months. There is no vertical transmission (not passed to the next mosquito generation) of the virus.

Outbreaks are usually confined since the flight range of A. aegypti is limited. Oftentimes the spread is house-to-house. Small and/or artificial water-collecting vessels and plants and trees that collect water in their nooks and crannies are the breeding sites of Aedes aegypti. Breeding booms during rainy season.

An infective mosquito bite will have clinical manifestations in humans after 2-14 days. In mild cases, there are only non-specific signs and symptoms. There may be fever, muscle and joint pains, headache, lymphadenopathies, and rash. This mimics other common viral infections. Working diagnosis depends on high suspicion. The clinical disease coincides with the viremia (virus in the blood). With proper supportive care (i.e. fluids, antipyretic, bed rest) cases may resolve without any problem in less than a week.

Dengue hemorrhagic fever is a more severe syndrome. This is what the attending physician is watching out for. There may be symptoms of headache, chills and body malaise preceding the onset of fever. The temperature pattern has a saddle-back form. There is fever in the first couple of days that subsides on the next 3 or 4 days then the temperature rises again. The rash may appear during the non-febrile stage then fades with desquamation after 3 days. Although the early stage is very similar to normal Dengue fever, the condition of the patient might suddenly worsen.

Dengue shock syndrome, characterized by hemoconcentration and shock, may set in without any warning. The pathogenesis of the syndrome is not yet fully understood. Under the microscope small blood vessels show swelling and edema around them. Certain chemicals (procoagulants and vasoactive mediators) are released causing widespread clotting of blood inside the blood vessels (disseminated intravascular coagulation).

Prevention of the occurrence of Dengue fever and its more severe form Dengue hemorrhagic depends on effective control of the Aedes aegypti population. Regular elimination of breeding sites and simultaneous fumigation can keep the numbers down. Early detection and intervention by your physician may prevent complications.