Cases of dengue fever, a potentially fatal viral illness transmitted by mosquitoes, are increasing worldwide. The rise in cases is happening in areas that have historically struggled with the disease as well as in regions where dengue was previously unheard of until recently, including France, Italy, and Chad. Just last week, health officials in Pasadena, California reported the first locally transmitted case of dengue fever. So, what is dengue fever and why is it spreading so rapidly?
Dengue fever is a viral illness transmitted by Aedes species mosquitoes. It can cause severe joint pain and is often referred to as “breakbone fever” due to its excruciating symptoms. The Aedes aegypti mosquito, which is responsible for many current outbreaks, originally lived in African forests and fed on animals. However, it spread to the rest of the world through trade routes and adapted to survive in urban areas, feeding on humans and breeding in small bodies of water found in discarded items like tires and bottle caps. As more people move to urban areas, especially in developing countries with lower-quality housing, they become more susceptible to the virus. Additionally, climate change is allowing the mosquito to thrive in new areas. Dr. Gabriela Paz-Bailey, chief of the dengue branch at the U.S. National Center for Emerging and Zoonotic Infectious Diseases, explains that rising temperatures and extreme weather events extend the habitat range of Aedes mosquitoes, aiding in their proliferation.
Dengue fever can range in severity from mild flu-like symptoms to more severe manifestations, including headache, vomiting, high fever, and intense joint pain. Full recovery can take several weeks. Approximately 5% of individuals who become ill with dengue progress to severe dengue, which can lead to plasma leakage from blood vessels and even organ failure. The mortality rate for severe dengue in treated individuals ranges from 2 to 5%, but without proper treatment, the mortality rate can be as high as 15%. Lack of access to medical care, especially in resource-strapped countries, can contribute to untreated severe dengue. Additionally, in areas where dengue is new, a delay in diagnosis may occur, further complicating treatment. This is a challenge both in countries like Chad and even in places like Pasadena, where healthcare providers may be unfamiliar with the disease.
Forty percent of the global population lives in areas where they are at risk of dengue infection, with tropical countries like Brazil being the most common hotspots for the disease. Those most susceptible to dengue are individuals living in housing that fails to protect them from mosquitoes. Research conducted in areas along the U.S. southern border, where the Aedes aegypti mosquito is prevalent, demonstrated that there were fewer cases of dengue on the American side compared to the Mexican side. This discrepancy was attributed to measures taken by people on the American side, such as using screens on windows and air-conditioners and practicing greater social distancing. By limiting exposure to mosquitoes and reducing the chances of bringing the virus into new areas, transmission rates are kept low.
While it is unlikely that dengue will become a serious problem in the United States if people continue their current practices, the expectation of increased dengue cases in the country is reasonable. Urbanization and climate change are contributing factors to the spread of dengue globally. Southern China serves as a cautionary example, with the incidence of dengue skyrocketing within just a year. The disease is not improving in endemic areas, leading to imported cases in the United States and other countries. Therefore, dengue remains a growing concern worldwide.
Currently, there is no specific treatment for dengue infection, and patients are only provided symptom management, such as pain medication. Antiviral drugs are currently being tested by pharmaceutical companies. As for vaccines, the development of a dengue vaccine has been complicated. Dengvaxia, a vaccine developed by Sanofi, caused more severe cases in vaccinated individuals who subsequently contracted the virus, leading to its withdrawal in some regions. The World Health Organization has recommended a new vaccine called QDENGA for children aged 6 to 16 living in high transmission areas, but it is not available in the U.S. at this time due to a dispute regarding the data used in its approval process.
In tackling dengue, some countries have had success with proactive measures. Singapore, known for its effective approach, inspects homes and construction sites for breeding areas, imposing high fines for non-compliance. However, not every country has the necessary resources to support such activities. Brazil and Colombia have successfully used a bacteria called Wolbachia. When Aedes aegypti mosquitoes are infected with this bacteria, they can no longer transmit the dengue virus. These countries have been mass-producing and releasing Wolbachia-infected mosquitoes to diminish the dengue-carrying mosquito population.