Dengue Fever – An Epidemic?Leave a comment

Dengue is a mosquito-borne viral disease that has rapidly spread in all regions of WHO in recent years. Dengue virus is transmitted by female mosquitoes mainly of the species Aedes aegypti and, to a lesser extent, Ae. albopictus. This mosquito also transmits chikungunya, yellow fever and Zika infection. Dengue is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature and unplanned rapid urbanization.

Severe dengue (also known as Dengue Haemorrhagic Fever) was first recognized in the 1950s during dengue epidemics in the Philippines and Thailand. Today, severe dengue affects most Asian and Latin American countries and has become a leading cause of hospitalization and death among children and adults in these regions.

There are 4 distinct, but closely related, serotypes of the virus that cause dengue (DEN-1, DEN-2, DEN-3 and DEN-4). Recovery from infection by one provides lifelong immunity against that particular serotype. However, cross-immunity to the other serotypes after recovery is only partial and temporary. Subsequent infections by other serotypes increase the risk of developing severe dengue

Transmission

The Aedes aegypti mosquito is the primary vector of dengue. The virus is transmitted to humans through the bites of infected female mosquitoes. After virus incubation for 4–10 days, an infected mosquito is capable of transmitting the virus for the rest of its life.

Infected symptomatic or asymptomatic humans are the main carriers and multipliers of the virus, serving as a source of the virus for uninfected mosquitoes. Patients who are already infected with the dengue virus can transmit the infection (for 4–5 days; maximum 12) via Aedes mosquitoes after their first symptoms appear.

The Aedes aegypti mosquito lives in urban habitats and breeds mostly in man-made containers. Unlike other mosquitoes Ae. aegypti is a day-time feeder; its peak biting periods are early in the morning and in the evening before dusk. Female Ae. aegyptibites multiple people during each feeding period.

Aedes albopictus, a secondary dengue vector in Asia, has spread to North America and more than 25 countries in the European Region, largely due to the international trade in used tyres (a breeding habitat) and other goods (e.g. lucky bamboo). Ae. albopictus is highly adaptive and, therefore, can survive in cooler temperate regions of Europe. Its spread is due to its tolerance to temperatures below freezing, hibernation, and ability to shelter in microhabitats.

Characteristics

Dengue fever is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death.

Dengue should be suspected when a high fever (40°C/104°F) is accompanied by 2 of the following symptoms: severe headache, pain behind the eyes, muscle and joint pains, nausea, vomiting, swollen glands or rash. Symptoms usually last for 2–7 days, after an incubation period of 4–10 days after the bite from an infected mosquito.

Severe dengue is a potentially deadly complication due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment. Warning signs occur 3–7 days after the first symptoms in conjunction with a decrease in temperature (below 38°C/100°F) and include: severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums, fatigue, restlessness and blood in vomit. The next 24–48 hours of the critical stage can be lethal; proper medical care is needed to avoid complications and risk of death.

Prevention and control

At present, the main method to control or prevent the transmission of dengue virus is to combat vector mosquitoes through:

• Preventing mosquitoes from accessing egg-laying habitats by environmental management and modification;
• Disposing of solid waste properly and removing artificial man-made habitats;
• Covering, emptying and cleaning of domestic water storage containers on a weekly basis;
• Applying appropriate insecticides to water storage outdoor containers;
• Using of personal household protection such as window screens, long-sleeved clothes, insecticide treated materials, coils and vaporizers;
• Improving community participation and mobilization for sustained vector control;
• Applying insecticides as space spraying during outbreaks as one of the emergency vector-control measures;
• Active monitoring and surveillance of vectors should be carried out to determine effectiveness of control interventions.

Careful clinical detection and management of dengue patients can significantly reduce mortality rates from severe dengue.

WHO advice

WHO promotes the strategic approach known as Integrated Vector Management (IVM) to control mosquito vectors, including those of dengue.

The proximity of mosquito vector breeding sites to human habitation is a significant risk factor for dengue virus infection.

Prevention and control relies on reducing the breeding of mosquitoes through source reduction (removal and modification of breeding sites) and reducing human–vector contact through adult control measures. Both control measures need to implemented simultaneously for effective control.

This can be achieved by reducing the number of artificial water containers that hold water (cement tanks for water storage, drums, used tyres, empty bottles, coconut shells, etc.) in and around the home and by using barriers such as insect screens, closed doors and windows, long clothing and use of insect repellents, household insecticide aerosol products, mosquito coils etc. and space spraying with insecticide can be deployed as an emergency measure. As protection from the Aedesmosquitoes (the primary vector for transmission), it is recommended to sleep (particularly young children, the sick or elderly) under mosquito bed nets, treated with or without insecticide.