BANGKOK—Scientists have discovered a new type of the virus that causes a centuries-old pestilence, dengue. The surprising find, announced at a major dengue conference here today, is bound to complicate efforts to develop a vaccine against a tropical disease that is becoming a more pervasive global menace. But it could shed light on where the pathogen came from and whether it is evolving into a greater threat. The finding “may change the way we think about dengue virus evolution and emergence," says Duane Gubler, a dengue expert at the Duke-NUS Graduate Medical School in Singapore.
There is no vaccine or drug against dengue, which is spread by mosquitoes and causes fever and sometimes excruciating joint pain and muscle aches. Patients typically recover on their own, though severe cases need medical support. Occasionally, the illness progresses to dengue hemorrhagic fever, a potentially fatal complication in which blood leaks through vessel walls. A dengue infection confers lifetime immunity to that particular type. But subsequent infection with a second type increases the likelihood of serious illness. With that in mind, vaccine developers have strived to protect against all four types simultaneously.
That may have gotten more challenging. By chance, researchers screening dengue viral samples found a virus collected during an outbreak in Malaysia's Sarawak state in 2007 that they suspected was different from the four original serotypes. They sequenced the virus and found that it is phylogenetically distinct from the other four types. Experiments found that monkey antibodies produced against the new type differ significantly from those resulting from the previously known dengue viruses. "We discovered and characterized a new dengue serotype," announced Nikos Vasilakis, a virologist at University of Texas Medical Branch in Galveston, here today at the Third International Conference on Dengue and Dengue Haemorrhagic Fever.
"They've done a very good job in characterizing the virus, and it's convincing that it is distinct from the other four," says Thomas Scott, a dengue expert at the University of California, Davis.
What it may mean for controlling dengue is unclear. So far, dengue 5 has been linked to only one outbreak in humans. Vasilakis suspects that it is circulating, possibly among macaques, in the forests of Sarawak. If it spreads, it could make human vaccine development more challenging. "We don't need another complication in controlling dengue," Scott says.
Current efforts to rein in the disease are falling short. In talks here today, researchers from Malaysia, the Philippines, and Thailand said that despite control programs launched in the 2000s, dengue cases are increasing, though the death toll is down thanks to better management of severe cases. "Dengue is spreading from urban to rural areas and to countries, such as Nepal, where it has not been seen before," said Samlee Plianbangchang, the World Health Organization Southeast Asia regional director. The annual global incidence, close to 390 million cases, is about three times the burden previously estimated, researchers reported in April in Nature.
Despite a recent setback in vaccine development, Plianbangchang said that projects in the pipeline have researchers "looking forward to a vaccine in the near future." But he adds that a vaccine will complement, not replace, efforts to contain dengue through mosquito control and public awareness. "Dengue will be with us for many years and could get worse," he said.