Mosquitoage > Background

Dengue fever.
Dengue fever is a mosquito-borne viral disease that occurs in over 100 countries worldwide (map) with the most significant epidemics occurring in Southeast Asia, the Americas and the Western Pacific. There are four dengue virus serotypes all of which can cause dengue fever (DF) and dengue haemorrhagic fever (DHF), a more severe and potentially fatal form of the disease. Dengue imposes a significant global disease burden with some 2.5 billion people - 40% of the world’s population - at risk of infection. The World Health Organization (WHO) reports 50 to 100 million cases of dengue annually.

Dengue became a widely established disease throughout the tropics with the development of commercial shipping during the 18th century. In 1905 during a large dengue outbreak in Brisbane (Queensland, Australia), local medical practitioner Thomas Bancroft was the first to demonstrate that the mosquito, Aedes aegypti, was a vector of dengue. The epidemiology of dengue was transformed in Southeast Asia during World War II. Troop deployments facilitated the movement of different dengue viruses across the region. This resulted in hyperendemicity (co-circulation of multiple dengue serotypes), a major factor related to the emergence of epidemic DHF in the Philippines and Thailand during the 1950s. By the 1970s regular DF/DHF epidemics were common throughout Southeast Asia.

In recent decades there has been a global resurgence of epidemic DF and DHF. Many factors are responsible for this widespread increase in dengue activity, however, it is clear that rapid population growth, urbanization and increased international air travel have all been driving forces associated with the explosive increase in dengue incidence. Rapid population growth and poorly planned urbanisation has lead to substandard housing, inadequate water supply and waste management systems. Consequently, storage of drinking water and other urban water sources (e.g. old tyres, litter) provides habitat for mosquito larvae. Aedes aegypti, the principal dengue vector, is adapted to these domestic environments and its distribution in urban areas has expanded. Increased air travel has facilitated the spread of dengue strains and serotypes between regions, increasing the prevalence of hyperendemicity and the risk of DHF.

Currently, there are no specific treatments or effective vaccines to fight dengue fever, therefore, disease monitoring and vector control programs are the only methods available for dengue prevention. However, these measures largely involve insecticide-based programs that are expensive to maintain and large-scale application often carry considerable environmental concerns.

Dengue transmission.
Dengue virus is transmitted by Aedes mosquitoes, primarily Aedes aegypti and Aedes albopictus. Aedes aegypti is referred to as a domestic mosquito as it lives in close association with humans and it is responsible for the majority of dengue transmission. The transmission cycle for dengue is human - mosquito – human. Only female mosquitoes bite, requiring the blood for egg production, and therefore only female mosquitoes transmit pathogens. A female mosquito may acquire dengue virus after ingesting blood from a person sick with dengue. It takes about 12 days for the mosquito to be capable to transmit the virus to a new person. During this time the virus replicates inside the mosquito body, spreading until it reaches the mosquito’s salivary glands. The virus is then injected with the saliva into a human whenever the mosquito takes a blood meal. Given that most mosquitoes live less than 30 days, only relatively old mosquitoes (those at least 12 days old) can transmit dengue virus to humans. If we can selectively remove the older individuals from a mosquito population it should effectively block disease transmission.

For information on current dengue activity and epidemics please refer to the following links:

Dengue and DHF outbreak information from WHO
www.who.int/csr/don/archive/disease/dengue_fever/en/
www.who.int/csr/don/archive/disease/dengue_haemorrhagic_fever/en/

Queensland, Australia
www.health.qld.gov.au/dengue/outbreak_update/default.asp

For additional information of dengue refer to the following links:
www.cdc.gov/ncidod/dvbid/dengue/
www.who.int/topics/dengue/en/
www.who.int/mediacentre/factsheets/fs117/en/
www.who.int/tdr/diseases/dengue/
www.health.qld.gov.au/dengue/