Zika Isn’t the Mosquito-Borne Virus You Should Fear
It was on her fifth day in the hospital in Bandung, Indonesia that Stevie Bergman finally lost it. She had checked in with a fever and a headache so severe that she wasn’t able to walk or eat; a friend half-carried her through the doors of the emergency room. The diagnosis: dengue, a mosquito-borne virus that is a scourge of tropical areas around the world. Over the next few days, she got weaker and weaker as her platelet count fell and her temperature climbed above 104°F. She didn’t have enough energy to spend any of it worrying, or even thinking about what was happening to her.
Then, on day five, the rash appeared. It covered her legs and back. “The nurses found me lying on the floor, because the floor was cooler, just screaming and crying and trying with all that I could not to scratch it,” remembers Bergman. “I still had a really low platelet count, so they warned me, don’t scratch because you’ll bleed, and bleed a lot. That was pretty harrowing.”
As fear of Zika sweeps the US, it’s easy to forget that so much of the world—including the places where Zika is hitting the hardest—already copes with mosquito-borne viruses whose typical symptoms blow Zika’s out of the water. I’m just going to say it: I’d rather get Zika than dengue fever. For most adults, Zika is like dengue-lite. You might get a rash, headache, and fever for a few days, but nothing on the order of what Bergman experienced.
Now, evidence is also gathering that Zika might also be associated with Guillain-Barré syndrome, in which your immune system goes into overdrive and causes temporary paralysis. But lots of viruses can cause Guillain-Barré. The scariest thing about Zika is its potential link to microcephaly, a birth defect in which babies are born with unusually small heads. If I got pregnant, I would worry about contracting Zika. But until then, dengue scares me a lot more.
And don’t even get me started on chikungunya, another virus transmitted by the Aedes aegypti mosquito. It arrived in the Caribbean in December 2013 and quickly spread across Latin America. I live in Mexico City, which is too high in the mountains for disease-carrying mosquitoes to reach. But I travel pretty frequently to lower-lying, more tropical parts of Latin America, and the possibility of coming home with one of these viruses is always on my mind.
The Tropical Threat
That’s what happened to Patsy Torres, who lives in Mérida, the capital of Yucatán state in Mexico. After a trip to Cancún, she came down with what she thought was a common cold—until she woke up the next day and couldn’t stand up. “The joint pain, especially in my feet, was really strong,” she says. That’s a telltale symptom of chikungunya. All the doctors could do for Torres was prescribe paracetamol—basic Tylenol. In addition to the excruciating joint pain, she had a fever of over 101°F for three days.
But however unpleasant the immediate symptoms of dengue and chikungunya are—and they are really unpleasant—what you really have to worry about is what could happen next. “They each have their own little shop of horrors,” says Peter Hotez, the dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston, Texas.
“The differentiator with chikungunya,” Hotez says, “is that 5 to 10 percent [of patients] will experience chronic joint symptoms, including pain and stiffness and swelling, that can persist for years.” Torres came down with the acute symptoms of chikungunya in August 2015, and she still has joint pain seven months later. “There are days when I wake up with the pain again, and I know exactly what it is,” she says. “It’s not as bad now, but I still feel it.” Her doctor told her the joint pain could linger for up to three years. There’s no treatment, much less a vaccine, which isn’t a valuable target for big pharmaceutical companies.
As for Bergman, she spent eight days in the Bandung hospital with dengue fever, and it took her another month to recover her strength. “Dengue was the biggest check-in with my own mortality that I’ve had,” she says. People in Indonesia seemed fairly nonchalant about the risk—houses without window screens were common, and pools of standing water lingered all over Bandung. But once someone heard that she had had dengue, the stories came pouring out. “Everybody knew somebody, and it might have been themselves, and probably more than one person,” she says. During one of her darkest moments at the hospital, a nurse commiserated by telling her, “I had dengue fever once. I wanted to die.”
Now, the disease is never far from Bergman’s mind, especially because she knows that if she ever catches dengue again, she could be in for something far worse. Dengue comes in four varieties—called “serotypes”—and catching one does not make you immune to the others. The antibodies you develop during that first case can actually give future dengue infections a boost. “The antibody can help facilitate virus entry into cells and make the disease worse,” says Hotez.
That nightmare scenario is called “immune enhancement,” and it’s how dengue can kill you. It’s also what makes developing a vaccine particularly difficult. “You have to develop immunity against all four serotypes,” Hotez says. “Because if you don’t develop antibodies against one of the serotypes, then there’s at least a theoretical concern that you might make things worse.”
Before moving to Indonesia with a Fulbright scholarship in 2013, Bergman had been a Peace Corps volunteer in Uganda and felt like she could handle any illness she encountered abroad. But that was before she knew about immune enhancement. “That’s when I got really sad, because I didn’t want to have to think about the places that I go in that way,” she says. “Of whether or not it would be wise for me to go to them because of the likelihood that I could die, basically, from getting dengue again.”
She’s back in the US now, and she thought long and hard about whether she should go on a beach trip last summer to Oaxaca, Mexico, a region that hosts both dengue and chikungunya. She decided to take the risk—but when it came up during an open-air yoga class that the town had recently suffered a chikungunya outbreak, Bergman didn’t think twice about running inside and slathering herself with mosquito repellant.
The Forensics of Fear
When Zika panic hit the US, I got huffy that its less novel cousins—and the suffering they cause every day—were being overshadowed. But Bergman doesn’t see it that way. When she got dengue, “most of my family thought it was nothing.” She doesn’t blame them; after all, she didn’t know anything about dengue either until it put her in the hospital. “With the Zika virus, people [in the US] are maybe getting a little bit more aware of dengue and chikungunya, which is really good,” she says. “We’re so isolated here.”
But maybe not for long. Hotez predicts that dengue, chikungunya, and Zika are likely to show up along the US Gulf Coast soon. “On the Gulf Coast, you’ve got the perfect storm of the Aedes aegypti mosquito, the warm subtropical climate, and poverty,” he says. That makes it more likely people will live without window screens and near standing water where mosquitoes can breed. And as the climate warms, mosquitos are only going to move farther and farther north, potentially bringing these diseases with them.
New infectious diseases can be even scarier than their immediate symptoms suggest because no one knows exactly what they’re capable of. The links between Zika and microcephaly (and Guillain-Barré) are getting stronger, but they aren’t a sure thing yet. Dengue and chikungunya, on the other hand, are known entities. Paradoxically, that can make it harder for citizens and policy makers to get worked up about them.
Despite the immune-enhancement challenges, scientists are making progress toward a dengue vaccine. Genetically-modified mosquitoes might prove successful at reducing the populations of the infectious critters. But it’s that last risk factor Hotez mentioned—poverty—that really helps keep these diseases in play. Until more people have access to safe, mosquito-free homes, these viruses aren’t going anywhere. If the world needs a dose of Zika panic to control mosquito populations and improve people’s living conditions, then that’s fine by me.