Maryland Department of Agriculture

Dengue is a widespread disease that occurs in much of the world primarily in the home range of its mosquito vectors, the yellow fever mosquito, Aedes aegypti and the Asian Tiger mosquito, Aedes albopictus. Dengue is becoming more common, especially in the Americas where mosquito control programs are reduced. Dengue occurs in multiple epidemics each year sometimes infecting many individuals in the human population. In 1997, thousands of cases were reported in India, Bangladesh and Singapore. Cases occur regularly in Puerto Rico and throughout Central and South America. Recent epidemics in the Americas occurred in Brazil and Cuba. We believe that monkeys are the reservoirs for maintaining this disease in its forest cycle.

Dengue occurs in three forms: classic dengue, dengue hemorrhagic fever, and mild dengue. The disease varies in severity but the death rate is usually less than 5 per cent. The incubation period is five to six days, often composed of two feverish periods. Symptoms of classic dengue include fever, joint ache, severe headaches, weakness, and skin rashes. This form is not fatal and rarely affects children. Mild dengue has the same symptoms but lasts just three days. Recovery is complete but weakness and depression can linger for weeks. Dengue epidemics are usually large and widespread and affect most of the population. They have extensive social implications because they reduce productivity and social organization.

Dengue hemorrhagic fever and the associated dengue shock syndrome (DSS) were originally found in Asia but in the early 1980s they were reported from Cuba. This form, unlike others, affects many children less than 15 years old. Symptoms are similar to those described but also include coughing, vomiting and severe abdominal pain. This disease causes abnormal blood clotting that can result in internal bleeding and organ failure, not to mention circulatory collapse. In addition, DSS affects the nervous system and causes convulsions. Epidemics of DHF/DSS have occurred in the Western and Eastern Hemisphere and thousands of deaths have resulted in many of the epidemics.

Recently, dengue has begun to spread and it is now found in many areas where it was eradicated. We have attributed the spread largely to the colonization of many areas with the vectors, the Asian Tiger mosquito and the yellow fever mosquito. Both mosquitoes live in much of the Eastern United States. In Maryland, tire importers introduced the Asian Tiger mosquito from Asia and it became established in Baltimore City. This species continues to spread in suburban areas and is a resident species in Prince George's and Montgomery Counties. We have also detected this mosquito in Charles, Talbot, Dorchester and Harford Counties. This species breeds in containers and tree holes. In the last ten years many yellow fever mosquitoes have been imported to Maryland, often resulting in large populations locally. These mosquitoes cannot live through the winter because temperatures in Maryland are too low for their survival.

E-Mail Jeannine Dorothy, Maryland Department of Agriculture Mosquito Control