Dengue Fever is on the Rise, Spreading Beyond the Tropics

The world is experiencing levels of Dengue Fever never before experienced in recent history. Without a vaccine, a disease once contained in the tropics may spread far across the globe.

Dengue Fever is a vector-borne viral infection transmitted between humans primarily by Aedes mosquitos. The World Health Organization considers it the most rapidly spreading vector-borne disease and is only second in severity to malaria. Once confined to the tropics, now about half of the world’s population live in areas where there is a risk of transmission.

The WHO estimates that between 50 and 100 million people are infected annually worldwide but a new study from Oxford University more than triples that number. The recent dramatic increase and global spread of the disease is attributed to climate change and a combination of other factors including urbanization, increased international travel, and population growth.

Dengue is characterized by rapid onset high fever, severe joint pain, a measles-like rash, vomiting and mild bleeding from the mucous membranes of the mouth and nose with symptoms lasting 5-7 days. Severe dengue is a rare but potentially lethal complication due to plasma leaking and fluid accumulation leading to severe bleeding and organ dysfunction. There is no vaccine for dengue and most people quickly recover but without proper access to medical care, the mortality rate can climb to over 20%. Prevention of the disease is accomplished through limiting contact with mosquitos and effective vector control, often costly and unaffordable to the most endemic areas.

The worst epidemic of dengue happened in 2010, with over 1.6 million cases in Latin America. So far this year, 1.4 million cases have been reported in the region and that number is set to rise with the increase of rainfall in the coming months. Honduras recently declared a state of emergency and has been particularly hard-hit with some 20,000 cases and 21 deaths. Costa Rica has detected over 33,000 cases and in Mexico, mass public awareness campaigns have been launched in response.

Asia has also seen a rapid emergence of dengue with India, Singapore, Philippines, and Laos reporting an increased number of cases and new occurrences in China and Pakistan. The threat of dengue in Europe also exists after an outbreak in Portugal last year and transmission being detected for the first time in France and Croatia. In the U.S., cases are emerging in Florida and Texas, sending areas into high-alert and even suspending blood collection efforts in several counties.

Dengue is particularly worrisome for low-income regions that lack funding for public awareness campaigns, vector control interventions or have little access to medical care. The WHO global strategy for the control of the disease proposes a 50% reduction in mortality by 2020 but without a vaccine, dengue will continue to emerge. Although developing a vaccine has been challenging, there has been significant recent progress in clinical studies by France’s Sanofi Pasteur. For now, it is a race against time between dengue vaccine development and the rapid spread of the burdensome disease.