In this and another building outside Havana, U.S. Army Maj. Walter Reed led an experiment that proved mosquitoes spread yellow fever. This photo was taken in 1948, half a century later. (Courtesy of Health Science Library/University of Virginia)

Ever since a U.S. Army physician named Walter Reed helped prove more than a century ago that yellow fever was transmitted by mosquitoes, humans have waged a fitful war on the tiny disease carriers. They have drained swamps and cesspools from Argentina to Alabama, waged door-to-door campaigns to hunt down breeding sites across entire cities, dumped an ocean’s worth of pesticides on multiple continents.

Without such efforts, the Panama Canal might never been finished in the early 1900s. Deadly outbreaks might have continued to ravage places as far north as Philadelphia.

But always, through a mixture of resiliency and adaptability, the mosquito roared back. People grew complacent. Political willpower faltered. Eradication budgets shrank. Chemicals lost their killing potency as the enemy developed resistance.

Now comes Zika, and yet another showdown. The mosquito-borne virus, which has raced through the Americas in recent months, is suspected of causing a range of serious, even devastating birth defects. Countries are once again calling for massive spraying efforts, renewed public education and collective vigilance from citizens. Some are considering new tactics such as genetically engineered mosquitoes that produce offspring that cannot survive to adulthood; the World Health Organization wants such unproven weapons evaluated with “particular urgency” and “extreme rigor.”

During construction of the Panama Canal in the 1910s, workers sprayed insecticides to kill mosquitoes and tamp down the diseases they carried. (Jacques Boyer/Ullstein Bild via Getty Images)

Everyone would do well to remember the lessons of the past.

Confirming a link

For all the justifiable concern about Zika, the harm it is causing is nothing like the scourge people throughout the Americas once faced from yellow fever and malaria.

Yellow fever decimated New Orleans in 1853 and parts of the Mississippi Valley in 1878. In the 1880s, thousands perished from both diseases during France’s failed attempt to dig the Panama Canal.

A Cuban scientist, Carlos J. Finlay, was the first to theorize that the mosquito might be the vector for such outbreaks — not foul odors, stale beer, swamp gases or any of the other popular myths of the time. He published his findings in 1881, but it wasn’t until the American occupation of Cuba after the Spanish-American War that he was proved right.

In June 1900, the U.S. Army sent Maj. Walter Reed to Havana to study Finlay’s findings about the spread of yellow fever. The selection was smart; the Virginian, a medical researcher as well as a physician, had previously investigated outbreaks of typhoid fever in military camps.

On a patch of land outside Havana, Reed designed two wood-framed, 14-by-20-foot buildings in which to conduct his experiments. Volunteers were offered $100, according to Stan Cope, president of the American Mosquito Control Association.

The buildings were known as the Fomite House and the Mosquito House. The first was fetid, filthy and unventilated. The men there slept with linens and blankets soiled with urine, black vomit and feces of recent yellow-fever victims — an environment that made some retch. But the house had no mosquitoes inside, and no one came down with yellow fever.

By contrast, the Mosquito House was clean and well ventilated. Its linens and furnishings were sanitized. Inside, a partition divided the space into two sections. On one side, researchers released infected mosquitoes, which fed on the volunteers. Many soon became ill, while those who slept on the mosquito-free side were fine.

“The experiments were incredibly simple, but they were absolutely bulletproof,” Cope said.

The outcome proved Reed — and Finlay — correct. Poor sanitation was irrelevant; mosquitoes were the vector for the disease. As Reed later wrote his wife, the test helped lift “the impenetrable veil that has surrounded the causation of this most dreadful pest of humanity and to put it on a rational & scientific basis.”

Soon, the Army was coating canals and waterways with a sheen of oil — a rudimentary larvicide — and attacking pools of stagnant water as part of public health and sanitation campaigns in countries where troops were stationed.

In 1912, New Jersey Gov. Woodrow Wilson (D) set up the United States’ first mosquito-control district after opponents accused him of being “weak on mosquitoes,” according to Gordon Patterson, a historian at the Florida Institute of Technology who has authored two books on the origins of U.S. mosquito control. Fighting the bloodsuckers soon became a primary government responsibility.

Mosquito control grew even more essential during the Great Depression, as the Tennessee Valley Authority and other agencies built dams, canals and reservoirs. Engineers learned to manipulate water levels to eliminate mosquito larvae, Patterson said. But by the late 1940s, manual mosquito-eradication methods were losing out to crop dusters and fumigation trucks loaded with the insecticide DDT.

And by the time Rachel Carson’s groundbreaking 1962 environmental-science book “Silent Spring” alerted the public to the pesticide’s dangers to birds and other wildlife, many mosquitoes had developed a resistance. For the past half-century, public-health officials have emphasized “integrated pest management” that involves more sparing use of insecticides and focuses on other solutions, such as window screens, mosquito repellent and the elimination of breeding pools.

Today, Patterson worries, increased travel, global commerce and possibly a warming planet all seem to be helping the mosquito to flourish again.

A uniquely adapted mosquito

Latin America has been hit especially hard by Zika, not to mention other viral pathogens such as dengue fever and chikungunya, in part because the Aedes aegypti mosquito is almost uniquely adapted to human co-habitation. It breeds in minute amounts of water, hides in the shadows and dark corners of homes, and is a famously promiscuous biter, landing on as many people as possible for quick snacks.

A much-heralded international effort in the 1940s and 1950s eliminated Aedes aegypti from 18 countries in the region, until that success reversed because of fading political will and rapid urbanization, among other issues.

The crowded, poverty-stricken sections of Central and South American cities, where uncollected trash, discarded containers and old tires are abundant, have proved a perfect setting for the disease’s spread. Many families without plumbing systems store water in tanks that are ideal spots for mosquitoes to lay their eggs. Homes also typically lack air conditioners and window screens — two factors that could limit the transmission of Zika in the United States.

Yet the Aedes aegypti mosquito has found ideal environments here, primarily along the Gulf Coast. Another mosquito, Aedes albopictus, which is viewed as a separate possible vector for Zika, has a much wider range across the United States.

Entomologist Janet McAllister of the Centers for Disease Control and Prevention is concerned by how much communities have let down their guard. “There is even [an environmental] movement here in the United States to start storing water again in rain barrels,” she said. “So we’re actually in some ways moving backwards in public health in terms of preventing mosquito breeding.”

As warm weather returns, the primary vector for Zika’s spread will begin to breed again in the Southeast. States and localities, potentially facing the most troubling mosquito-borne disease outbreak in decades, are gearing up for the fight with a mix of old and new tools. President Obama is seeking $1.9 billion from Congress for the effort, including money for spraying, spreading larvicide and ramping up mosquito abatement.

Relatively few Americans may realize how central such work once was to the nation’s identity. Because these insects carried disease, their extermination became an essential government service, another chapter in the long campaign to tame the wilderness.

But the war wasn’t over and may never be, as the Zika virus is making clear.

“We thought we had taken care of the Aedes mosquito,” McAllister said. “Now, the problem has come back to haunt us.”