Mosquitoes — and diseases like Zika — flourish when economies tank

The news out of Puerto Rico is grim: Not only has the Zika virus infected nearly 25,000 people so far, including almost 1,700 pregnant women, but the US government has appointed a Financial Control Board to oversee the territory’s government spending as it tries to cope with a nosediving economy and crippling debt. With few job prospects, Puerto Ricans are leaving the island in droves, often abandoning their homes. A failing economy, empty homes, and the outbreak of Zika: The three are related.

Serious public health challenges often flourish in struggling economies because the habits and movements of people change. Yet health authorities rarely treat migration as a marker of public health concern.

Take, for example, Venezuela, where the travels of wildcatting gold miners has resulted in a resurgence of malaria after the country had been malaria-free for more than half a century. Urban Venezuelans — computer technicians, civil servants, and the like who had fallen on hard times due to inflation and a crashing economy — set off for the edge of the rainforest to pan for gold in massive muddy gold mines abandoned by the government. Mosquitoes that still harbor the malaria parasite breed in the stagnant water around the squatters’ camps, biting and infecting the miners. With the collapse of the Venezuelan economy, drugs for preventing and treating malaria are scarce. And as malaria-stricken wildcatters head home, they are spreading the disease, beaten down a generation ago, in major cities.

Read more: Puerto Rico is being pummeled by Zika, with hundreds of cases of birth defects feared

Such public health threats aren’t restricted to less developed nations. It happened in Florida during the Great Recession. Beginning in late 2007, hundreds of thousands of Floridians went into foreclosure after the subprime mortgage crisis, leaving thousands of stagnant abandoned backyard pools — perfect breeding grounds for mosquitoes. In 2009, the Sunshine State saw a severe and surprising spike in cases of dengue, which went hand-in-hand with the housing crisis.

Roughly 100,000 people have left Puerto Rico in the last year, many of them abandoning their homes. A University of California, Berkeley, professor has compared this shift to the Dust Bowl migrations of the 1930s. The island is losing roughly a doctor a day, straining the health care system. These shifts have helped the Zika virus gain a stronghold in Puerto Rico.

Of course, slumping economies and empty pools aren’t the only factors favoring Zika. Funding still plays the most critical role in the fight against diseases of public health significance. The US government’s slow movement on Zika-specific funding likely hindered progress in the early fight against the disease in Puerto Rico, and with the economy in collapse, local funds have been strained.

Not all outbreaks, of course, happen in economic downturns. The 2014 appearance in Florida of chikungunya, another infectious disease carried by mosquitoes, and the recent discovery of more areas of Miami with Zika-infected mosquitoes both occurred during a rebound in the housing market, which presumably included better-attended, cleaner pools.

It’s hard to predict the pattern of transmission for infectious diseases. But we do know the conditions that help them spread. Economic downturns consistently signal changes in human activity and patterns — the abandonment of construction sites when the market slows down, an increase in homeless encampments near mosquito breeding sites, increases in migration, and more. These, in turn, can affect the transmission of infectious diseases not only because of cuts in public health funding but because of changing economic conditions which affect on-the-ground transmission of diseases.

Read more: What the world has learned about Zika — and what it still needs to know

A further threat comes from climate change, which is lengthening the mosquito season and expanding breeding grounds for mosquitoes. Climate change’s new ecological patterns require us to double down on our efforts to more quickly respond to the inevitable economic shifts.

While we can’t always anticipate how an economic slump will fuel infectious disease, we should ensure that we have robust health planning in place. Our lack of foresight is most obvious in that we seem to have ceased considering public health needs as ongoing, long-term, inevitable, and constantly shifting. In the US, we don’t have enough resources to be reactive, let alone proactive.

In addition to improving our responses to public health emergencies, we must provide long-term funding to let public health authorities take into account the changing nature of human behavior in response to economic changes. The health of all of us depend on it.

Amy K. Liebman is the director of environmental and occupational health for the Migrant Clinicians Network, a nonprofit organization based in Austin, Texas.