DENGUE: Public Health Issues & Key Facts

Adeno-Associated virus
Courtesy of VIRUSWORLD

Dengue remains a public health problem in most if tropical countries especially in Asia, Africa and South America despite the efforts to stop and mitigate the impact of epidemics. It is a dynamic systemic infectious disease. The infection can be asymptomatic or show with a broad clinical spectrum that includes serious and non-serious ways of expression. After incubation, the disease begins abruptly and goes through three phases: The febrile, critical, and recovery stage. Dengue needs to be addressed as a single disease with different clinical presentations ranging from benign conditions to severe clinical courses and outcomes that may lead to death.

 

Key facts1

  • Dengue is a mosquito-borne viral infection.
  • The infection causes flu-like illness, and occasionally develops into a potentially lethal complication called severe dengue.
  • The global incidence of dengue has grown dramatically in recent decades.
  • About half of the world’s population is now at risk.
  • Dengue is found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas.
  • Severe dengue is a leading cause of serious illness and death among children in some Asian and Latin American countries.
  • There is no specific treatment for dengue/ severe dengue, but early detection and access to proper medical care lowers fatality rates below 1%.
  • Dengue prevention and control solely depends on effective vector control measures.

 

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, A. albopictus. The disease is widespread throughout the tropics, with local variations in risk influenced by rainfall, temperature and unplanned rapid urbanization.

Severe dengue (also known as Dengue Hemorrhagic 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 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.

 

Global burden of dengue1

The incidence of dengue has grown dramatically around the world in recent decades. The actual numbers of dengue cases are underreported and many cases are misclassified. One recent estimate indicates 390 million dengue infections per year (95% credible interval 284–528 million), of which 96 million (67–136 million) manifest clinically (with any severity of disease).1 Another study, of the prevalence of dengue, estimates that 3900 million people, in 128 countries, are at risk of infection with dengue viruses.2

Member States in 3 WHO regions regularly report the annual number of cases. In 2010, nearly 2.4 million cases were reported. Although the full global burden of the disease is uncertain, the initiation of activities to record all dengue cases partly explains the sharp increase in the number of cases reported in recent years.

Other features of the disease include its epidemiological patterns, including hyper-endemicity of multiple dengue virus serotypes in many countries and the alarming impact on both human health and the global and national economies.

Before 1970, only 9 countries had experienced severe dengue epidemics. The disease is now endemic in more than 100 countries in the WHO regions of Africa, the Americas, the Eastern Mediterranean, South-East Asia and the Western Pacific. The America, South-East Asia and Western Pacific regions are the most seriously affected.

Cases across the Americas, South-East Asia and Western Pacific exceeded 1.2 million in 2008 and over 3 million in 2013 (based on official data submitted by Member States). Recently the number of reported cases has continued to increase. In 2013, 2.35 million cases of dengue were reported in the Americas alone, of which 37 687 cases were of severe dengue.

Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are occurring. The threat of a possible outbreak of dengue fever now exists in Europe and local transmission of dengue was reported for the first time in France and Croatia in 2010 and imported cases were detected in 3 other European countries. In 2012, an outbreak of dengue on the Madeira Islands of Portugal resulted in over 2000 cases and imported cases were detected in mainland Portugal and 10 other countries in Europe.

In 2013, cases have occurred in Florida (United States of America) and Yunnan province of China. Dengue also continues to affect several South American countries, notably Costa Rica, Honduras and Mexico. In Asia, Singapore has reported an increase in cases after a lapse of several years and outbreaks have also been reported in Laos. In 2014, trends indicate increases in the number of cases in the People’s Republic of China, the Cook Islands, Fiji, Malaysia and Vanuatu, with Dengue Type 3 (DEN 3) affecting the Pacific Island countries after a lapse of over 10 years. Dengue was also reported in Japan after a lapse of over 70 years. In 2015 an increase in the number of cases was reported in Brazil and several neighboring countries. The Pacific island countries of Fiji, Tonga and French Polynesia have continued to record cases.

An estimated 500 000 people with severe dengue require hospitalization each year, a large proportion of whom are children. About 2.5% of those affected die.

 

Transmission1

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 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. Aegypti bites multiple people during each feeding period.

Aedes albopictus, a secondary dengue vector in Asia, has spread to North America and Europe largely due to the international trade in used tires (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.

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References;
  1. Dengue and severe dengue Available from: http://www.who.int/mediacentre/factsheets/fs117/en/. Accessed at January 14, 2016.
  2. Brady OJ, Gething PW, Bhatt S, Messina JP, Brownstein JS, Hoen AG et al. Refining the global spatial limits of dengue virus transmission by evidence-based consensus. PLoS Negl Trop Dis. 2012;6:e1760. doi:10.1371/journal.pntd.0001760.
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