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Mosquito control could slow the spread of disease in a warming world

Mosquito control could slow the spread of disease in a warming world


Diseases and disasters

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Anopheles gambiae mosquito.
Anopheles gambiae mosquito.
Photo by BSIP / UIG via Getty Images

The recently announced Green New Deal, a resolution to help address the threats of climate change, gives public health advocates a chance to confront an overlooked consequence of climate change: worsening mosquito-borne illnesses.

The resolution, which outlines projects designed to boost renewables, reduce emissions, and climate-proof the country’s infrastructure, was introduced by Rep. Alexandria Ocasio-Cortez (D-NY) and Sen. Ed Markey (D-MA). Its goal is to extinguish potential economic, national, and social infernos that are brought on by climate change. But the plan also recognizes growing threats to public health, such as the diseases becoming far more common in a warming world.

Climate change has already expanded the reach of mosquitoes that carry certain illnesses. More extreme weather events are also part of the package, and more severe storms, stronger hurricane seasons, more floods and droughts also increase the risk of disease after a natural disaster. According to the World Health Organization (WHO), climate change could increase the number of people who are at risk of malaria by over 100 million.

No national body currently oversees mosquito control

In the US, the ability to quickly take action varies wildly, according to Dan Strickman, a medical entomologist for the Bill & Melinda Gates Foundation. No national body currently oversees mosquito control. Instead, those responsibilities fall to the county level where necessary control programs often fail to make it onto budgets, Strickman says. The leader in the US is Florida, according to Strickman, where 61 of 67 counties have their own mosquito control programs. Those programs came in handy when Zika popped up in Miami in 2016. The virus ran wild in South America, but it was very well contained in Florida. “Not every state is like that,” says Strickman. “That’s a huge vulnerability.”

Quick responses are crucial for public health threats. When it comes to mosquito-borne illnesses, that often requires insecticide. Climate-related natural disasters, like floods, can mean stagnant water blanketing millions of acres, which are ideal places for mosquitoes to lay their eggs. In 2017, after Hurricane Harvey flooded southeast Texas, which is susceptible to the West Nile virus, the Air Force deployed planes for two weeks of aerial spraying across nearly 3 million acres. However, aerial spraying isn’t 100 percent effective, and it’s expensive; that two-week mission likely cost upward of $2 million.

that two-week mission likely cost upward of $2 million

According to Strickman, large-scale mosquito control is essential but notoriously difficult. He says we should address this problem by educating people in mosquito-prone areas. Many governments allocate funds to teach people how to reduce mosquito breeding sites. But Strickman says these programs are often too passive, relying solely on brochures and websites. Research shows that person-to-person engagement is more effective and cheaper than more passive campaigns. With the Green New Deal, we could see national efforts directed toward doing just that. The new plan resolved to mitigate the public health effects of climate change by “providing funding for community-defined projects and strategies.”

The reality of climate and disease

When the West Nile virus first arrived in the US in 1999, we were unprepared. As we slowly got up to speed to respond, it spread across the country. Now, whenever more intense hurricanes hit, post-storm West Nile virus transmission is a constant threat. “It took about three years to get that response together,” says Strickman. “Now it’s established, and we’ll never get rid of it.”

“Now it’s established, and we’ll never get rid of it.”

The national resources that do exist to prevent diseases like the West Nile virus are minimal and variable. In 2017, the Centers for Disease Control and Prevention (CDC) funded five Vector-Borne Disease Centers of Excellence at universities across the country. But the centers, which primarily focus on research and training, each operate quite differently from one another, according to Strickman, and control efforts remain largely decentralized. Strickman imagines that additional resources could help stifle potential outbreaks more effectively, wherever they emerge.

Clusters of mosquito-borne disease occur throughout the world, especially in densely populated countries with less developed health care systems. But that doesn’t mean that the US is immune to outbreaks originating on foreign soil. Diseases don’t respect borders. Disease in all corners of the world could be considered a threat to the US’s national security, says Scott Dowell, an infectious disease specialist at the Bill & Melinda Gates Foundation. So we should fundamentally care about helping all countries address their local disease outbreaks.

For Ann Powers, chief virologist for the CDC, that vulnerability to mosquito-borne disease is familiar, as is its connection to climate change. In 2005, Powers traveled to the Comoro Islands off the southeast coast of Africa to respond to an outbreak of chikungunya. She says the outbreak began because of a human response to extreme weather.

Mosquitoes need water in order to lay their eggs. Since many viruses depend on mosquitoes to spread, water can be a welcome mat for dangerous disease. According to Powers, a severe drought in nearby Kenya forced people to collect any available water and store it in giant barrels. These barrels basically invited chikungunya-carrying mosquitoes to lay their eggs near people’s homes. The virus spread from mainland Africa to a quarter million people in nearby islands before arriving in India, where it infected over 1 million people.

diseases don’t respect borders

Chikungunya — like some other mosquito-borne diseases — is rarely fatal, but it’s debilitatingly painful, Powers says. Some patients she met in the Comoro Islands could hardly use their hands, and others couldn’t stand. “I think that as soon as you see a patient or someone who is sick with one of these agents, it gives you the human face of what’s actually going on,” she says.

In late July 2018, heavy rainfall in Sudan caused severe flooding and destroyed homes. Reports of both dengue and chikungunya viruses popped up soon after. By October, tens of thousands were infected, and dozens died.

The problem isn’t just chikungunya and dengue, however. Mosquitoes spread Zika and West Nile after major disasters, too. According to Raman Velayudhan, a specialist in vector control with 30 years of experience with WHO, all four viruses threaten almost everyone on Earth. The mosquitoes carrying these diseases thrive in stagnant water. So areas with poor drainage and lots of people — like cities — are hot spots. Velayudhan says that climate change is making disease transmission worse. Couple the uncertainty of disease outbreaks with that of extreme weather, and it’s clear why this problem is dangerously unpredictable.

“You don’t know what it will be or where it will be or who it will affect,” Powers says about the vulnerability for all countries, including the United States. “Simply not knowing what’s coming next is always a challenge.”

What preparedness looks like

In an ideal world, response to an outbreak begins long before any natural disaster. Public health audits, disease surveillance, and reporting systems are a top global priorities to keep outbreaks under control, but it will take a sustained, persistent effort to be successful.

Just look at what happened in South America over 60 years ago. In the 1950s, Brazil successfully eradicated its population of Aedes aegypti — a main carrier of dengue, Zika, yellow fever, and chikungunya — using a combination of insecticide and sterile male mosquitoes. The international effort spanned North and South America, including the US. Countries committed their resources to decimate Aedes aegypti populations systematically, and the program was heavily centralized with “military-type organization.” According to Strickman, the use of sterile, or “inert,” males to snuff out future generations was instrumental to its success. By 1962, 18 countries had eradicated the species.

But that success was fleeting. “One of the reasons it failed was because the United States failed to do its part,” says Strickman. “They didn’t put enough resources in it. They weren’t emphatic enough about it.” Within a few years, the mosquito populations from countries like Venezuela and the US reinfested the other nations. If the program had succeeded, Strickman says, the 2015 Zika outbreak would not have happened.

“the United States failed to do its part.”

With the Green New Deal, there’s a chance that more resources could be routed to preventing climate-related disease. Strickman is optimistic that new technologies and a more centralized approach would help. Phone apps to crowdsource reports of foreign mosquitos can impede new diseases. Rebooting — and committing to — mosquito eradication can eliminate existing ones.

In 2017, Fresno, California, began its own mosquito-eradication program with inert male Aedes aegypti. But, even if successful, Aedes aegypti populations elsewhere in the country make Fresno vulnerable to reinfestation. That vulnerability highlights a recurring theme echoed by both Ocasio-Cortez on climate and experts on mosquito-borne disease: we don’t exist in isolation, and solving our biggest problems requires a committed, concerted effort.