Trinidad and Tobago continues to be on a dengue alert. In an effort to increase awareness of the disease and how it is transmitted, the following information was compiled from various fact sheets about dengue:

DHF/DSS is characterized by a sudden onset of fever, usually of two to seven days duration, and a variety of non-specific signs and symptoms.

During the acute phase of the illness, it is difficult to distinguish DHF/DSS from dengue fever and other viral illnesses. The critical stage of DHF/DSS occurs most frequently from 24 hours before to 24 hours after the temperature falls to or below normal.

During this time, haemorrhagic manifestations usually occur, and more importantly, signs of circulatory failure may appear.

Clinical laboratory tests at this time will show a platelet count of less than 100,000/mm3 and evidence of a capillary leak syndrome, which is not corrected with fluid replacement therapy, may cause shock and death.

The most common haemorrhagic manifestations are skin haemorrhages, but bleeding gums and gastrointestinal haemorrhage can also occur.

The incubation period for DHF/DSS can be as short as three days and as long as 14 days. The average incubation period is four to six days.

Dengue viruses are transmitted by day-biting Aedes mosquitoes. The most important mosquito vector is the highly domesticated and urban species Aedes Aegypti. Secondary mosquito vectors include Aedes Albopictus, Aedes Polynesiensis and other species.

Mosquitoes may become infected when they take a blood meal from a viremic person. Viremia is present for about 24 hours prior to onset and for an average of five days after onset of illness, usually coinciding with the period of fever.

Mosquitoes that become infected from viremic blood require a period of incubation of about 8 to 12 days, depending on the temperature, before they can transmit dengue viruses to another person.

During this time the virus grows through the midgut and infects a number of tissues in the mosquito, including the salivary glands. Transmission requires the infective mosquito to take another blood meal, or to probe an individual in search of blood.

Multiple feedings or probing by an infective mosquito may result in transmission to multiple persons in the same household or building, all having onset of illness within a few days of each other.

The best way to avoid dengue infection is to avoid Aedes Aegypti Mosquito bites. The highest risk of dengue infection occurs in tropical urban areas.

The mosquito vectors of dengue are day-biters, with peak feeding activity in the morning for several hours after daybreak and in the late afternoon for several hours before dark.

However, these mosquitoes may feed throughout the day in the shade, indoors, or on overcast days.