What is the fastest growing mosquito-borne disease in the world? (HINT: It’s not Zika!)
Zika and Yellow Fever have been vying for the spot of the most talked about insect-borne disease lately, but one mosquito-borne disease has been consistently spreading over the past 50 years. Dengue is ranked by the World Health Organization (WHO) as the most important and fastest growing mosquito-borne viral disease in the world today, causing nearly 500 million infections every year.
In the last 5 decades, dengue has spread from being present in a handful of countries to being endemic in 128 countries, where about 4 billion people live. Dengue cases have also increased 30-fold in this time period. In addition, more people are travelling than ever before and millions of travelers to endemic areas are also at risk of being bitten by the disease-carrying mosquitoes. Dengue has important economic consequences because of the significant burden on communities, hospitals, work absenteeism and risk of death of serious cases.
Dengue is transmitted primarily by the Aedes aegypti mosquito, the same mosquito that transmits West Nile virus, Zika and chikungunya. Vector control has been the primary method of disease control - strategies include covering, emptying and cleaning of domestic water storage receptacles, applying insecticides to outdoor water storage containers, and using personal household protection, such as window screens, long-sleeved clothes, and insecticide treated materials, coils and vaporizers. However, in dengue-endemic countries, it has been shown that, despite extensive vector control efforts, outbreaks of dengue still occur and the number of cases remains high.
Progress and developments in the fight against dengue
Over the last several years, much progress has been made towards the development of safe and effective dengue vaccines and mosquito control strategies can now be supplemented by vaccination. Dengvaxia (produced by Sanofi Pasteur) is the first (and currently only) dengue vaccine approved in 14 countries like Philippines, Mexico, Brazil, Thailand, Singapore, Indonesia, Paraguay, Costa Rica, El Salvador, Peru and Guatemala where dengue is endemic. The vaccine has received endorsements from key medical societies; the Latin American Society for Pediatric Infectious Diseases (SLIPE - Sociedad Latino Americana de Infectología Pediátrica) published its support for dengue vaccination consistent with the WHO’s position paper recommending use as part of an integrated dengue management program in countries with a high burden of disease. At least two other vaccines are expected to be available in the coming years. In clinical trials, none of the vaccines guarantee 100% protection from infection. What it does, however, is reduce the severity of illness when a person gets infected. US National Institute of Health’s (NIH’s) TV-003 (licensed to the Butantan Institute in Brazil and Panacea Biotech/Biological E in India) aims to enroll 17,000 healthy people aged 2 to 59 years for the Phase III trials. Some 20,000 children will be inoculated over the next 3 years in Asia and Latin America with Takeda’s TAK-003 dengue vaccine. An inactivated vaccine is currently being evaluated jointly by GSK and Walter Reed Army Institute of Research (WRAIR) and a recombinant subunit vaccine is being developed by Merck.
Other novel methods used to reduce mosquito population include the placement of copepods or guppy in standing water to eat the mosquito larvae. There are also trials with genetically modified Aedes aegypti that mate with females and render their offspring unable to fly.
A recent advancement in controlling dengue and other mosquito-borne flaviviruses (dengue, West Nile virus, Zika, yellow fever are flaviviruses) is with the use of a bacterium called Wolbachia. Mosquitoes infected with this bacterium are resistant to subsequent flavivirus infection, and the bacteria are able to infect and persist within mosquito populations. Since 2011, field trials have shown that when a high proportion of mosquitoes in an area carry Wolbachia, local transmission of viruses is stopped. The Eliminate Dengue Program (EDP) has launched projects in India, Brazil, Australia, Indonesia, Vietnam and Colombia
A proactive and integrated approach is important to control dengue
Aside from vector control strategies and vaccines, it is also important to improve community awareness and participation and promote active monitoring and surveillance of mosquito vectors and dengue disease in clinics and hospitals. The burden of disease from dengue is expected to rise due to factors such as the modern dynamics of climate change (i.e. warmer conditions brought about by the El Nino weather phenomenon), globalization, travel, trade, and viral evolution and the fast breeding and maturation cycles of the Aedes mosquito population.
No specific antiviral therapy exists, but after decades of research, we now have a vaccine. A vaccine could have a major public health impact if the particular disease has a high incidence. The effect on the overall incidence of dengue will depend largely on the number of people who become vaccinated. The approach to dengue is almost always reactive – only when there is an outbreak. It is important to be pro-active in controlling dengue before it becomes an even greater threat. An integrated approach of vector control, public awareness, monitoring and surveillance, and vaccination will lead to great progress in the control of the disease and will eliminate dengue as a public health problem firstly in endemic areas.
This article is part of HuffPost’s Project Zero campaign, a yearlong series on neglected tropical diseases and efforts to eliminate them. This series is supported, in part, by funding from the Bill & Melinda Gates Foundation. All content is editorially independent, with no influence or input from the foundation. If you’d like to contribute a post to the series, send an email to ProjectZero@huffingtonpost.com. And follow the conversation on social media by using the hashtag #ProjectZero.
Dr Melvin Sanicas, vaccinologist and public health physician, is a regional medical expert at Sanofi Pasteur, a consultant for the World Health Organization, and an agenda contributor for the World Economic Forum.