It doesn’t have its celebrity fundraisers, unlike AIDS. It hasn’t made the headlines in the way that bird flu or SARS have. It isn’t feared in the way that polio or TB are, and yet dengue fever can kill and is spreading around the world to an unprecedented degree.
The latest figures from the World Health Organization (WHO) suggest that annual transmissions of the disease may breach 390 million. This year, infections are breaking records all over Asia and Latin America — from sweeping epidemics in Nicaragua to the worse outbreaks in six years in India, 20 years in Thailand and the first homegrown case in Western Australia in seven decades. Even temperate climates are now stalking grounds for dengue-carrying mosquitoes.
Almost 3 billion people, or 40% of the world’s population, live in areas where there is a risk of dengue transmission. Previously known as breakbone fever, owning to the excruciating muscle and joint pain inflicted, dengue first came to the fore in Southeast Asia during World War II, when large numbers of troops were afflicted with it. Up until the 1960s the disease was largely controlled with DDT, which decimated mosquito populations. But the mosquitoes crept back after the chemical was banned for its severe side effects and ever since “we have seen an ever increasing march of the virus into new territories and new recipient populations,” says Paul Young, professor at the University of Queensland in Australia and president of the Australian Society for Microbiology, who has been researching dengue for almost three decades.
Mention dengue and most people will think of aches and chills. But the disease is far more dangerous than that. Dengue causes white-blood-cell counts to plummet, making the body susceptible to secondary infections; even more alarmingly, it has a similar effect to platelets, impairing blood’s ability to clot. If left untreated, and particularly on a second infection, dengue hemorrhagic fever can take hold, and patients can suffer internal bleeding, shock and death.
While malaria rates have fallen 25% worldwide since 2000 — including a 35% drop in Africa, according to the WHO — dengue is seeing a dramatic upsurge. “South America is gearing up for a huge epidemic,” says Young. Asia has been particularly hard-hit, with 51,000 dengue cases in Cambodia and Laos; 96,000 in the Philippines; 135,000 in Thailand; 18,000 in Malaysia; and 15,000 in Singapore by the start of September. The U.S. has not been spared either, with the first case in a major city in Houston and “serious levels” in Florida.
Dengue exacts its greatest toll among young children, those with underlying health issues or those do not seek proper medical treatment. Financially — both from medical treatment and lost workdays — it costs billions of dollars globally each year. “It has been a never-ending cycle of increasing numbers,” says Young.
The reason for the swell is simple: vector control. Mosquitoes have more places to breed now that chemical spraying is less effective, and population clusters give the disease areas to propagate. This now includes the temperate climates of Europe and North America. Scientists say global warming may play a part — since associated higher rainfall creates more stagnant water that in turn allows more mosquito larvae to hatch. Young says that dengue’s move “into more temperate zones” is among his greatest concerns, and adds that many major U.S. and European cities will be susceptible to dengue should the trend continue.
So what about a vaccine? Dengue has five strains (the most recent was discovered in Malaysia, although scientists are playing down the risk to humans of that strain) and while some can be vaccinated against, so far protection from all of them has proved elusive. France-based Sanofi Pasteur, the world’s largest vaccine firm, had a inoculation slated for rollout in 2015, but trials earlier this year confirmed protection from only three out of the four dangerous strains. The company still intends to mass-produce the vaccine, and stage-three trials are now under way in Asia and Latin America involving 31,000 subjects. Nonetheless, the partial protection “was a surprise and we need to think more about how dengue works and research,” Dr. Melanie Saville, Sanofi Pasteur chief medical and clinical officer for dengue, tells TIME.
Faced with such challenges, scientists have searched for alternative ways of combating the disease. The team at Eliminate Dengue has been breeding genetically superior mosquitoes infected with Wolbachia bacteria, which essentially prevent the insects from getting dengue (although scientists are not sure exactly why). When released into the general population, these mosquitoes take over their dengue-prone cousins. Trials are currently ongoing in Vietnam with impressive results. “It’s a great piece of science and community engagement,” says Young.
The one thing that will accelerate research into dengue is the new threat it poses to the world’s wealthier regions and countries — however unfair that may seem. Big Pharma does not traditionally focus on developing world problems — Eliminate Dengue’s pioneering work is largely thanks to largesse from the Bill & Melinda Gates Foundation — but when affluent markets are in the firing line, attitudes change rapidly. “The amount of research work that was going into West Nile virus before it hit New York and spread across the States in 1999 was miniscule,” says Young, “and you can imagine the change. The same thing might happen with dengue.”