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Why we still don’t know all of the ways you can contract Zika

Reuters/Paulo Whitaker
Just scratching the surface.
Published This article is more than 2 years old.

A unique case of Zika in the state of Utah has raised an alarm in the scientific community. A man contracted the virus through contact with his elderly father, who had 100,000 times as many viruses in his blood as a normal infected person. The father died—the first Zika-related death in the US—but the son recovered. Yet we still don’t know how the son contracted the virus in the first place.

The Utah man’s case is one among millions since the Zika outbreak began in early 2015 in Brazil. The arbovirus, which was first discovered in 1947, hadn’t infected more than a few thousand people in any earlier outbreak and, thus, hadn’t been studied that well. We know that, like dengue or malaria, the main mode of transmission is through mosquitoes. Then recent research confirmed that it can be occasionally transmitted through sexual intercourse. But the Utah case has highlighted that we still don’t know all of the ways that Zika is transmitted.

It has been six months since the World Health Organization (WHO) declared Zika a public-health emergency—only the fourth in the organization’s 70-year history. The unknowns make it difficult to acquire funds to develop effective measures to protect people. Though the WHO’s recommendation has been to avoid mosquitoes and unprotected sex with at-risk people, what else should we be doing to stay safe?

Answering that question is hard and what we are learning reveals what we must change about public health before a deadlier new contagion strikes.

The fear of the unknown

In the latest outbreak, Zika has shown an uglier side. After months of research, we now know that Zika causes devastating birth defects, and may cause Guillain-Barré syndrome, which leads to (often temporary) paralysis. Zika has left thousands of children disabled and possibly hundreds of adults paralyzed.

When the outbreak began, we knew that the main mode of transmission was Aedes aegypti (and, to a lesser extent, Aedes albopictus). But the virus has infected so many more people than ever before, leaving scientists to surmise that mutations may have enabled it to spread via other more common species of mosquito or even completely new modes.


Last week, researchers in Brazil released preliminary results suggesting Zika can be carried by Culex quinquefasciatus mosquitoes, a different species of mosquito that is much more common in rural parts of Brazil. “It means that we have a second species of vector involved in transmission,” Constancia Ayres, a researcher from the Oswaldo Cruz Foundation in Brazil who led the study, told the Washington Post.

The mighty mosquito

But the scientific community remains cautious about these results. Though Culex is able to carry Zika, the researchers haven’t proven that it can also transmit the virus to humans.

“It’s not right to say that if it’s in a mosquito species, then it’s a vector,” said Fiona Hunter, a biologist at Brock University in Ontario. “But if it’s in a mosquito species, there should really be some follow up.”

The process to determine whether a mosquito is a vector of a disease is difficult. First, researchers need to collect or rear mosquitoes of a particular species. Then they need to feed it blood that contains the disease contagion, such as the Zika virus. Ideally, small batches of mosquitoes will be fed blood samples containing different levels of the contagion. Next, they need to determine if the virus survives in the mosquito. If it does, then the researchers have to feed the infected mosquitoes on an animal, usually small mammals like mice. Finally, they need to find out if the bite has infected the mammal with the contagion.


“Few places in Brazil have the sophisticated equipment to do all this,” said Jimmy Whitworth, an infectious-disease expert at the London School of Hygiene and Tropical Medicine. “Even fewer have equipment that can analyze samples at high throughput. So for most places it’s a slow and laborious process.”

The findings about Culex quinquefasciatus carrying Zika were first presented at a summit in March, but they are yet to pass the rigorous scrutiny needed to be published in a scientific journal. What makes their case harder to prove is that a recent study by the US Centers for Disease Control and Prevention (CDC) on Culex pipiens, another species of mosquito, which is commonly found in the US, showed that it wasn’t able to carry the Zika virus.

Frustratingly, the lack of clarity so far means that no one knows if greater protective measures must be taken.

What about the man who contracted Zika in Utah? It’s possible that Zika can pass through other bodily fluids, though much less frequently. ”I would guess the caregiver got infected via virus-containing saliva or urine,” said Vincent Racaniello, a virologist at Columbia University. “We know the virus can be in these fluids and it’s not hard to imagine getting contaminated with them while caring for a sick person.” Separately, Davis Fernandes Ferreira, a virologist at the Federal University of Rio de Janiero, speculated that if these fluids could carry Zika, it’s also possible that breast milk could too.

The lack of clarity so far means that no one knows if greater protective measures must be taken. Currently, the CDC hasn’t said that caregivers should wear more protective gear when handling Zika patients. And if the virus can be transmitted through Culex mosquitos, the current protocols in place for curbing mosquito transmission wouldn’t cut it. Culex mosquitos are much more widespread—20 times more than the Aedes mosquitos, according to the study—and mostly in rural areas as opposed to cities. Aedes likes to live behind closed doors of human homes, breed in small containers of clean water, and bite in the hours after sunrise and before sunset. Culex lives in the open, breeds in large pools of dirty water, and bites at night.

It’s not the WHO’s job

In face of these uncertainties what have officials, including the World Health Organization (WHO), been doing to understand Zika?

The WHO has had to deal with two massive outbreaks in the last two years, Ebola and Zika. Even though Ebola didn’t spread to too many countries, it killed 11,000 people. Zika is not as deadly, but it has spread rapidly across all of South America and threatens to spread in the Northern hemisphere as summer progresses. Unlike Ebola, Zika hasn’t been well studied.

These have been two very different beasts, yet the WHO has learned from its failures during the Ebola crisis and applied those lessons to the Zika epidemic.

First, the WHO was quick to recognize the scale of the problem and declare Zika a public-health emergency early on. Second, during Ebola, the WHO’s communications about the risks weren’t clear enough and that was partly to blame for the uncontrollable spread within affected countries. But in Zika’s case, the WHO didn’t shy away from the unknown risks and it was clear in communicating precaution: avoid mosquitoes using protective gear and repellants and don’t have unprotected sex if you’ve been to a Zika-affected country. It even suggested delaying pregnancy for women living in affected areas.

Some of this has been effective. As the chart shows, researchers believe that Zika may have peaked in Central and South America (though the Northern hemisphere remains vulnerable). And, yet, it seems surprising that after all these efforts we still lack some of the most basic information about the virus and how it spreads. But Whitworth isn’t surprised. “You’re expecting too much from the WHO,” he said.

“It isn’t the WHO’s role to organize and orchestrate research programs.”

“It isn’t the WHO’s role to organize and orchestrate research programs,” he said. “It has a framework. It disseminates that. Sometimes it organizes meetings to get people to think about how they will move forward on that. But largely you need to leave the research community to take up that challenge. And that doesn’t happen in any sort of general, co-ordinated way. It happens according to people’s expertise and interest.”

Whitworth says that the burden of basic research lies with countries enabling their researchers to do the work needed. Though the WHO employs experts, it has always been resource-limited. The organization set up a contingency fund of $100 million to help it during such emergencies, but that amount is not enough to run large-scale research programs needed to understand a new contagion.

Governments around the world have failed to provide adequate funding for the WHO’s efforts—compromising its capacity to effectively tackle the pandemic, which is ultimately where true progress could be made. When even resource-rich countries, like the US, aren’t ready to provide the funds needed to fight a crisis like Zika, despite the threat to its own population, it’s hard to expect other countries to step up to the task. So the blame lies rather on how we have setup and supported a global institution to deal with an unpredictable threat that knows no borders.

