Female Aedes Aegypti

• A smallish, dark mosquito with conspicuous white markings and banded legs; the proboscis is all black although the palps are white tipped.
• The mosquito originated from Africa but is now found in the tropics worldwide.
• Adults are also found within or close-by human environments, often biting indoors or in sheltered areas near the house; biting is predominantly by day in shaded areas but may also occur early in the night.
• Can be an important domestic pest but is of principal concern as major vector of Dengue fever and Yellow fever; potential vector of dog heartworm, and Murray Valley encephalitis and Ross River viruses.

A TEM micrograph showing Dengue virus virions (the cluster of dark dots near the center).

There are 2 types of dengue which most people wouldn’t know – dengue (DF) and dengue hemorrhagic fever (DHF). Both are caused by one of four closely related, but antigenically distinct, virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4), of the genus Flavivirus. Dengue fever is a flu-like illness spread by the bite of an infected mosquito while dengue hemorrhagic fever is a severe, often fatal, complication of dengue fever.

Dengue fever symptoms

Symptoms are most commonly seen in adults and older children. Young children may show no symptoms. Typical symptoms may include:

• sudden onset of fever (lasting three to seven days)
• intense headache (especially behind the eyes)
• muscle and joint pain (ankles, knees and elbows)
• unpleasant metallic taste in mouth, loss of appetite, vomiting, diarrhoea, abdominal pain
• flushed skin on face and neck, fine skin rash as fever subsides
• rash on arms and legs, severe itching, peeling of skin and hair loss
• minor bleeding (nose or gums) and heavy menstrual periods
• extreme fatigue

Dengue haemorrhagic fever symptoms

This is a rare complication of dengue in Australia. More commonly seen in children aged under 15 years, but can occur in adults. Symptoms include:

• same signs as dengue fever
• 2-5 days after onset of fever, rapid deterioration and cardiovascular disease
• perhaps shock and sometimes death.

Map: World distribution of dengue viruses and their mosquito vector, Aedes aegypti, in 2008

Dengue viruses occur in most tropical areas of the world. Dengue is common in Africa, Asia, the Pacific, Australia, and the Americas. It is widespread in the Caribbean basin. Dengue is most common in cities but can be found in rural areas. It is rarely found in mountainous areas above 4,000 feet.

The mosquitoes that transmit dengue live among humans and breed in discarded tires, flower pots, old oil drums, and water storage containers close to human dwellings. Unlike the mosquitoes that cause malaria, dengue mosquitoes bite during the day.

Antigens are large molecules (usually proteins) on the surface of cells, viruses, fungi, bacteria, and some non-living substances such as toxins, chemicals, drugs, and foreign particles. The immune system recognizes antigens and produces antibodies that destroy substances containing antigens.

Treatment
There is no specific treatment for dengue. Persons with dengue fever should rest and drink plenty of fluids. They should be kept away from mosquitoes for the protection of others. Dengue hemorrhagic fever is treated by replacing lost fluids. Some patients need transfusions to control bleeding.

Aspirin and non-steroidal anti-inflammatory drugs should be avoided. Acetaminophen (Tylenol) and codeine may be given for severe headache and for the joint and muscle pain (myalgia).

Prevention

• Improve water storage practices. Cover all containers to prevent egg laying female mosquitoes access to it.
• Eliminate any sources that may collect water such as tins, bottles, plastic food containers and old tires. Mosquitoes breed easily in any source of standing water.
• Appropriate insecticides, such as larvicide’s can be added to water containers and man-made ponds. The insecticides can prevent mosquitoes breeding for several weeks. However, they must be re-applied as per directions.
• Always clean and check drains to ensure they are not blocked especially during the rainy season.
• Breed small mosquito-eating fishes in an artificial pond to eradicate the mosquito larvae.
• Avoid wearing dark and tight clothing because mosquitoes are attracted to dark colours. Wear loose, white and long clothes, which cover the whole body. Mosquitoes find it difficult to bite through loose clothes than tight fitting clothes.
• Environmental conditions. It is suggested to sleep under mosquito netting or in a room which has mosquito screens on the windows. Mosquitoes are unlikely to bite in an air-conditioned room and under strong fans. Mosquito coils are also useful to help prevent mosquitoes from entering the room.
• Apply mosquito repellants.
• Avoid reduce outdoor activities during morning and late afternoon because Aedes mosquitoes are daytime feeders.

For more details:
Contact Dengue Operations Centre at
603-5123 7251 or 603-51237252

Reference:
MedicineNet.com – Dengue Fever
MedicinePlus – Dengue
WHO – Dengue
WHO – Dengue haemorrhagic fever: diagnosis, treatment, prevention and control. 2nd edition. Geneva : World Health Organization.