The risk of contracting dengue disease is increasing across many parts of Asia and the Pacific Islands. Countries like the Philippines, Malaysia, Sri Lanka, and Bangladesh that already suffer from high rates of dengue infection are reporting a surge in disease activity over the last 12 to 15 months.
According to the World Health Organization, dengue fever is one of the top 10 global health threats. Dengue is an infection found in tropical and subtropical climates worldwide. It is spread by mosquito bites and can cause a severe flu-like illness. Dengue is the fastest-spreading mosquito-borne illness in the world and is closely associated with rainy periods when the mosquito vectors can multiply at high rates. There has been an unusual amount of rainfall since June 2022 in the APAC region, accompanied by high temperatures and high humidity, which have resulted in an increased mosquito population.
Globally, the virus currently infects between 100-400 million people a year, with around 100 million reporting clinical symptoms and up to 40,000 fatalities. In the 1950s and 1960s, the disease was restricted to a few southeast Asian countries, but regional and worldwide dengue epidemics began in the 1970s and spread in the next two decades. In the 1980s, there were fewer than 15 million estimated infections. Dengue disease has steadily increased in the past 50 years because of various factors, including global trade and travel, urbanization, population growth, and climate variability and change, all of which provide conducive conditions for dengue vectors (like Aedes mosquitoes) and viruses to multiply. Dengue virus has the potential to cause epidemics resulting in high morbidity and mortality.
Dengue virus has four ‘serotypes’ or strains labeled 1 to 4, and it is possible to be infected by each one separately. Infection with one strain provides long-term immunity but only to that specific numbered strain; further infections put people at greater risk for severe dengue. Usually dengue causes a mild flu-like illness, while over 80 percent of cases are asymptomatic. However, some people with dengue develop complications that can result in internal bleeding, shock, and even death.
The mosquitoes which transmit dengue predominately bite during the day, between dawn and dusk, and they are particularly persistent and aggressive. The highest rates of infections tend to be in urban and semi-urban settings and are concentrated in major cities such as Manila or Dhaka. The proximity of mosquito breeding sites, such as stagnant water collections, to human habitation, is a significant risk factor for dengue virus infection. Although dengue does not directly spread from human to human, Aedes species mosquitoes can become infected after biting dengue-infected individuals, thus creating a cycle of transmission capable of spreading dengue and leading to clusters of cases.
The reason there are clusters is indeed due to transmission between closely grouped people but not through direct transmission. Where there is a densely populated group, there is more likelihood that s mosquito will take a blood meal from one infected person and then feed on another person in close proximity and thus transmit the virus between the two- and then on to the next person. The mosquitoes do not stray very far but can easily infect several members of a household and neighboring families.
The prevention and control of dengue is largely dependent on effective control of the mosquito vectors. These preventative measures include removing potential breeding sites, reducing vector populations, and minimizing individual exposure. Vector control activities should focus on all areas where there is a risk of human-vector contact (residences, workplaces, schools, and hospitals). Vector control activities include covering, draining, and cleaning household water storage containers on a weekly basis; space-spraying enclosed areas with insecticide; and chlorination for water storage in outdoor containers.
Personal protective measures during outdoor activities include the topical application of DEET-based repellents to exposed skin or on clothing and the use of long-sleeved shirts and long pants. Indoor protection can include the use of household insecticide aerosol products or mosquito coils. Window, door screens, and air-conditioning can reduce the probability of mosquitoes entering the house. Insecticide-treated nets offer good protection to people against mosquito bites while sleeping, remembering that Aedes mosquitoes are particularly active at dawn and dusk.
Travelers should be aware of symptoms in order that they can seek medical attention at an early stage. There is no specific treatment for dengue, but supportive treatment can be given in a hospital environment if severe symptoms develop. The advice is to protect yourself by preventing mosquito bites. There is no commercially available vaccine for “travelers,” but a limited-use vaccine is available for local populations at risk.
Dengue Vaccine
Recently, a vaccine against dengue has been developed and licensed to protect specific populations. It took three years of clinical trials to iron out the problems with the current vaccine, Dengvaxia, produced by the pharmaceutical company Sanofi. The vaccine had already been given to over a million children in the Philippines in 2016 before the vaccination program ended amid scandal a year later. Dengvaxia was eventually found to increase the risk of dengue in people who had not already been infected, and it is now only given to a limited age group with documented evidence of previous infection with dengue. The vaccine requires three shots given over a period of one year.
Dengvaxia can still potentially benefit a carefully chosen population. The US Food and Drug Administration (FDA) approved the vaccine in May 2019, but with tight restrictions limiting its use to children between the ages of 9 and 16 who have laboratory evidence of a prior dengue infection and live in areas where the virus is endemic. Puerto Rico and a handful of other US territories have endemic dengue. The FDA has not approved the dengue vaccine for use in travelers and non-residents of areas where dengue is common.
Dengue Key Points:
- Dengue is transmitted mainly by the Aedes Aegypti mosquito, which thrives in densely populated tropical climates and breeds in stagnant pools of water.
- It is prevalent in countries with hotter climates, such as Southeast Asia, Africa, Australia, the Caribbean, and South and Central America
- It is the fastest-spreading mosquito-borne illness in the world
- Symptoms are unpleasant and include high fever, severe headaches, vomiting and joint pains- it is known as ‘break-bone fever’- it usually resolves within a week
- There is no specific drug to treat the disease
- Dengue can become severe within a few hours. Severe dengue is a medical emergency, usually requiring hospitalization
- It kills around 40,000 people a year and infects between 100-400 million
- There is a vaccine, but it is limited to people who have already had the disease and has a limited age range from 9 to 45 years of age- a new vaccine is in development
- Prevention is, therefore by avoiding being bitten by mosquitoes with the use of DEET insecticides, suitable clothing that covers the skin, and bed nets
- Dengue exacts a heavy economic burden on countries as sufferers are unable to work and health services are overwhelmed during outbreaks
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