Dengue fever is having a big summer, with outbreaks being reported in tropical countries around the world.
While there are already about 390 million dengue infections every year, the World Health Organization expects the number of cases of the mosquito-borne illness to continue to grow, as climate change and other environmental factors create more habitats for disease-carrying mosquitoes to breed.
Here’s what you need to know about dengue.
What is dengue?
Dengue is a viral infection transmitted primarily by the Aedes aegypti mosquito, which is found mostly in tropical regions. To a lesser extent, the Aedes albopictus mosquito also carries the disease.
There are around 390 million dengue infections per year, according to the World Health Organization’s estimates, of which only about 96 million result in symptoms of dengue fever.
If you’re bitten and contract the infection, symptoms usually appear within five or six days and no later than 14 days, said Dr. Isaac Bogoch, an infectious disease specialist at Toronto General Hospital.
“Typically people who have an infection with this will have a fever,” he said. “They often have a headache; they often get muscle and joint pains.”
Headaches are typical too, he said. “There’s a classic description of pain behind the eyes.”
Many people, he noted, don’t develop symptoms at all, and the vast majority of people who do get sick see the infection clear up in a few days.
But occasionally, the disease can be more severe — and potentially, even deadly.
“There are severe cases and unfortunately they have to be dealt with in hospitals,” he said.
Although it’s quite rare to get a severe infection, the WHO says, symptoms can include plasma leaking, severe abdominal pain, bleeding gums and blood in vomit. Some people do die from dengue, but early detection can help to reduce that number.
While there isn’t a specific treatment for dengue, treating severe cases usually involves reducing fever, making sure a person stays hydrated and other supportive care, Bogoch said.
Which countries are reporting outbreaks?
In recent weeks, outbreaks have been reported in the Philippines, which has seen 146,000 cases and 622 deaths.
Bangladesh has seen 17,000 cases — the worst outbreak since 2000, according to official figures.
Sri Lanka has seen 234,000 cases and 47 deaths so far this year, according to the government. Fifty-eight deaths were recorded in all of 2018.
Honduras has also seen an outbreak, according to local media.
“It is probably too early to know what the actual burden of disease is this year compared to past years, but certainly it appears that it might be worse this year,” Bogoch said.
Before 1970, only nine countries had experienced severe dengue epidemics, the WHO said. Now, dengue is endemic to more than 100 countries.
In 2010, there were 2.2 million reported cases of dengue fever worldwide. In 2016, there were 3.34 million, according to the WHO. Bogoch said that these numbers likely underestimate the disease, as many infections, particularly mild ones, wouldn’t be formally reported.
“A vast majority of cases are asymptomatic and hence the actual numbers of dengue cases are underreported and many cases are misclassified,” the WHO said.
Why are dengue cases increasing?
It could be many things, Bogoch said. First, it’s possible that countries have gotten better at reporting cases.
Second, he said, we might be breeding more mosquitoes.
“They need freestanding fresh water or freestanding water to transmit infection,” he said.
“So urban areas are perfect because there’s lots of different places where water can be trapped and make little puddles.”
The World Health Organization tweeted this week that climate change is increasing the risk of dengue. Rainfall, warmer temperatures and rapid urbanization all mean that more people are getting dengue, they wrote.
Bogoch also noted that it’s easier for a traveller infected with dengue to get on a plane, get bitten by a mosquito back home, and so, transmit the infection to his homeland nowadays, compared to when travel was less accessible.
How can you keep yourself safe from dengue?
If you’re planning to travel internationally, Bogoch recommends that you visit a travel health clinic to find out about the risks of various illnesses, including dengue.
However, there’s currently no commercially-available vaccination for dengue, he said, although researchers are working hard on it.
Instead, most precautions involve protecting yourself from mosquitoes. Staying in accommodations with air conditioning and sealed windows can help keep mosquitoes from getting in, he said.
“When people are out and about, they should be wearing mosquito repellent, insect repellant with DEET or icaridin,” he said.