Dengue Fever: Understanding Dengue Transmission

March 12, 2024

Dengue Fever: Examining the Multi-faceted Dynamics of Dengue Transmission: From Mosquito Vectors to Maternal Transmission and Beyond

Dengue, or break-bone fever, is a viral illness transmitted to humans by mosquitoes, primarily prevalent in tropical and subtropical regions. While many individuals infected with dengue may not exhibit symptoms, those who do may experience high fever, headache, body aches, nausea, and rash. Most people recover within 1–2 weeks, but some may develop severe dengue, requiring hospitalization. In severe cases, dengue can be life-threatening.

Symptoms

The symptoms of dengue typically manifest 4–10 days after infection and can last for 2–7 days. These symptoms include high fever, severe headache, pain behind the eyes, muscle and joint pains, nausea, vomiting, swollen glands, and rash. Individuals who have had dengue before are at a higher risk of developing severe dengue, characterized by symptoms such as severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums or nose, fatigue, restlessness, blood in vomit or stool, extreme thirst, pale and cold skin, and weakness.

Diagnosis and Treatment

Most cases of dengue fever can be managed at home with pain medication. The primary focus of treatment is to alleviate the associated symptoms. Acetaminophen (paracetamol) is commonly used to control pain, while non-steroidal anti-inflammatory drugs like ibuprofen and aspirin are avoided due to their potential to increase the risk of bleeding. Dengvaxia, a vaccine, is available for individuals who have previously had dengue and reside in areas where the disease is prevalent. Severe cases of dengue often require hospitalization.

Global Impact

The incidence of dengue has escalated globally, with reported cases to the World Health Organization (WHO) increasing significantly from 505,430 in 2000 to 5.2 million in 2019. However, many cases go unreported due to being asymptomatic or mild and often mistaken for other febrile illnesses. It is estimated that there are 390 million dengue virus infections annually, with 96 million showing clinical symptoms. Dengue is now endemic in over 100 countries across various WHO regions, with the Americas, South-East Asia, and the Western Pacific being the most seriously affected. Furthermore, the disease is spreading to new regions, including Europe, with notable outbreaks reported in various countries.

Current Situation

As of 2021, dengue continues to impact several countries, including Brazil, Colombia, Fiji, India, Kenya, Paraguay, Peru, the Philippines, the Reunion Islands, and Vietnam. Notably, 2019 saw the highest number of reported dengue cases globally, with all regions affected, including the first recorded local transmission in Afghanistan. The American Region reported 3.1 million cases, with over 25,000 classified as severe, while high numbers of cases were also reported in Bangladesh, Malaysia, the Philippines, and Vietnam in Asia.

Transmission of Dengue Virus

Transmission through the mosquito bite

The dengue virus is primarily transmitted to humans through the bites of infected female Aedes aegypti mosquitoes, with other Aedes species also capable of transmitting the virus.
After feeding on a person infected with the virus, the virus replicates in the mosquito before moving to other tissues, including the salivary glands. The time it takes for the virus to be transmitted to a new host is called the extrinsic incubation period (EIP), which typically ranges from 8 to 12 days at temperatures between 25–28°C.
Factors such as temperature variations, virus genotype, and initial viral concentration can influence the EIP.
Once infectious, a mosquito can transmit the virus for the rest of its life.

Human-to-mosquito transmission

Mosquitoes can become infected by biting people with dengue virus in their blood, even before the person shows symptoms or after their fever has resolved.
The risk of mosquito infection is higher with high viremia and fever, while DENV-specific antibodies can decrease the risk of mosquito infection.
Viremia in infected individuals typically lasts for about 4–5 days but can persist for up to 12 days.

Maternal transmission

While mosquito vectors are the primary mode of DENV transmission between humans, there is evidence of the possibility of maternal transmission from a pregnant mother to her baby, which can lead to adverse outcomes for the baby.

Other transmission modes

Rare cases of transmission via blood products, organ donation, transfusions, and transovarial transmission within mosquitoes have been recorded.

Risk Factors and Prevention

Risk factors

Previous dengue infection increases the risk of developing severe dengue.
Urbanization, especially unplanned, is associated with dengue transmission through factors such as population density, human mobility, and water storage practices.
The community’s risk of dengue depends on its knowledge, attitudes, and practices towards the disease, as well as the implementation of sustainable vector control activities.

Prevention and control

Dengue-carrying mosquitoes are active during the day, and preventive measures include wearing protective clothing, using mosquito nets and repellents, and maintaining window screens.
Management of dengue involves rest, adequate hydration, use of acetaminophen for pain, and avoiding certain drugs. Currently, the Dengvaxia vaccine is approved in some countries, but it only protects individuals with evidence of past dengue infection.

WHO Response to Dengue

The World Health Organization (WHO) responds to dengue outbreaks by supporting countries in outbreak confirmation, providing technical guidance, improving reporting systems, offering training, formulating strategies and policies, and supporting the development of prevention and control strategies.
Additionally, WHO gathers official records of dengue and severe dengue from over 100 Member States and publishes guidelines and handbooks for surveillance, case management, diagnosis, and prevention and control of dengue for Member States.

References:

1. World Health Organization. (2023). Dengue and severe dengue. https://www.who.int/news-room/fact-sheets/detail/dengue-and-severe-dengue. Accessed March 12, 2024

2. Bhatt, S., et al., The global distribution and burden of dengue. Nature, 2013. 496(7446): p. 504–507.

3. Brady, O.J., et al., Refining the global spatial limits of dengue virus transmission by evidence-based consensus. PLOS Neglected Tropical Diseases, 2012. 6(8): p. e1760.