Epidemiology of dengue
Dengue is becoming a major health problem which is both global and local. Dengue fever outbreaks have been documented on every continent except Antarctica. Dengue-like disease was first described clinically in Thailand from 1950 and in Philippines from 1953. For more than 40 years, countries endemic for Dengue have reported cases and deaths to the respective World Health Organization Regional Officers.
Brief epidemiological aspects in relation dengue is given below.
Millions of people living in tropical and subtropical parts of the world are infected by one or more of the four serotypes of dengue viruses (DENV1-4) each year. Several hundred thousand of these infections, especially among children, progress to a life threatening disease known as dengue hemorrhagic fever (DHF). Dengue thrives in urban settings that support large populations of the mosquito vector and the human host. Dengue viruses, transmitted by infected Aedes mosquitoes, is considered to be the most important mosquito-borne viral disease affecting humans today.
World Health Organization estimates that dengue puts at risk the health of more than 2.5 billion people in the world (WHO 2000). Others estimate global burden as 3.5 billion people which is more than half the world population (Beatty 2010). It is also thought that as many as 1 in every 100 people are infected with a dengue virus each singe year (Harris 2008). Based on statistical modeling methods it is estimated that between 50 million (WHO 2000) and 500 million (Beatty 2010) people get infected with a dengue virus each year in over 100 countries. Of these infections between 500,000 cases (WHO 2000) to 2 million (Beatty 2010) DHF cases are estimated annually. It is also estimated that around 21,000 deaths are likely be occurring due to the server form of the disease annually (Beatty 2009).
Dengue is endemic in Africa, the Americas, the Eastern Mediterranean, the Western Pacific and in South-East Asia. The WHO South-East Asia (SEA) Region together with Western Pacific Region is responsible for nearly 75% of the global disease burden (WHO 2010).
According to the WHO countries in the South-East Asia Region are stratified into four categories based on number of criteria; Category I is a) where dengue has become a major public health problem with epidemics caused by multiple serotypes b) where there is high morbidity and mortality in children, c) where cyclical epidemics occur in urban centers, d) where the disease is spreading to rural areas and e) where multiple serotypes are co circulating - at present five countries in this group include Indonesia, Thailand, Myanmar, Sri Lanka and Timor-Leste. Category II is a) where cyclical epidemics are becoming more frequent, b) Multiple serotypes circulating c) Expanding geographically within the countries – at present three countries in this group include – Bangladesh, India and Maldives. Category III is where endemicity is uncertain with Bhutan and Nepal included in this category both reporting outbreaks in 2004 and 2006 respectively. Category IV is DPR Korea where there is no evidence of endemicity established (WHO 2010).