The Fever: How Malaria Has Ruled Humankind for 500,000 Years (25 page)

In fact, to control malaria transmission, it isn’t necessary to slaughter every last mosquito or avoid every last mosquito bite. Only certain species of the
Anopheles
mosquito need to be tackled, and even then only in ways that make it difficult for them to transmit the malaria parasite. As Manson pointed out, getting bitten ten times a night in a place where one out of every one thousand
Anopheles
is infected results in three malaria infections a year. Reducing those bites to one a week would result in just one bout of malaria in
ten years
.
⁶⁷

In the polarized debate Ross sparked, however, such nuances were quickly lost. “The identification of mosquitoes has become so difficult that it is better to leave it alone,” said the bacteriologist Robert Koch, “so long as there remains anything else to be done in this world.”
⁶⁸
Even in Italy there was little interest in controlling mosquitoes. Nobody seriously considered that all the Italian peasants sleeping in caves in the Campagna could be rid of every last mosquito bite. It was impractical, inconceivable.
⁶⁹
According to the Indian
Medical Service’s malaria expert Sydney Price James and the Dutch malariologist N. H. Swellengrebel, mosquito killing was “futile” and a “tyranny . . . over men’s minds” that should be “thrown off,” as they jointly reported for the League of Nations’ Malaria Commission in 1927.
⁷⁰

Ross died in 1932 a bitter, ruined man. “I had lost money over the work, I had received practically nothing but skepticism or even abuse in return, and most of my results were credited to others,” he wrote in his memoirs. “The word ‘malaria’ ” he declared, made him “nearly as sick as the thing itself would have done.”
⁷¹
To add insult to injury, the species of
Anopheles
named after him—
Anopheles rossi
—for years was believed not to transmit malaria.
⁷²
When it was finally discovered that it did, it had by then come to be known as
Anopheles subpictus
, the name bestowed upon it by Ross’s archrival Giovanni Grassi.
⁷³

In the decades following Ross’s and Grassi’s discovery, only those willing to flout the scientific conventional wisdom did anything much to minimize the reproduction or biting of malarial mosquitoes. The Italian prime minister Benito Mussolini did, during the 1930s, as a cornerstone of his Fascist revolution. His 549-million-lire scheme to finally drain the Pontine swamps took the lives of more than three thousand workers.
⁷⁴
Industrialists with malaria-threatened rubber plantations in Malaysia did, discovering that disrupting malaria transmission sent other infectious diseases—diarrhea, dysentery, nephritis, abscesses, tuberculosis, convulsions—plummeting as well.
⁷⁵

So, too, did American malariologists. Insect destruction was generally quite popular in the rapidly industrializing United States of the late nineteenth and early twentieth centuries. American farmers, having turned the wilds into feeding troughs for insects shorn of their natural enemies, lived in fear of entomological invasion. Clouds of locusts descended upon the farms of the Mississippi Valley. Gypsy
moths stripped every tree in New England of their leaves, and their decaying, crushed bodies sent a stench across the land.
⁷⁶

With insects strangling American economic development, the government had started to invest in entomological research. An early result, in 1901, was an influential handbook called
Mosquitoes: How They Live, How They Are Classified, and How They May Be Destroyed.
⁷⁷
Whether or not anti-mosquito campaigns alleviated malaria, they almost always helped improve property values, spur development, and after the First World War, showcase new chemicals, many of which had been refined for use as chemical weapons.

New Jersey state entomologist John B. Smith demolished acres of mosquito habitat in that state’s lowlands, a feat that he claimed more than quadrupled property values. A similar campaign waged on Staten Island, in New York City, triggered a development boom.
⁷⁸
In the early years of the twentieth century, the notorious oil baron John D. Rockefeller created the philanthropic behemoth the Rockefeller Foundation, whose International Health Division quickly gravitated toward the popular anti-mosquito projects. “I can’t recollect when we have been able to remain on our front porches without fighting the blood sucker until this summer,” one grateful local wrote to the foundation. “Thank you again.”
⁷⁹

None of this budged the scientific consensus against mosquito killing in Europe. The Rockefeller Foundation malariologists made the rounds at international scientific meetings, touting their entomological victories, but with notoriously poor data collection and a chronic lack of controlled comparisons, Rockefeller scientists’ optimistic reports left their European colleagues entirely unmoved. The reports didn’t measure whether malaria had declined, nor the complicated role of the many confounding factors—including rainfall, temperature, and the movement of human populations—that may have played a role in any observed changes. In 1927, the League of Nations prepared a report dripping with skepticism about the Americans’ claims.
⁸⁰

Rather than debate the issue and refine their science, the Americans, like Ross and Manson, closed ranks. Enraged American malariologists felt that their dismissive European colleagues couldn’t be bothered doing anything about malaria.
⁸¹
The U.S. surgeon general pressured the League of Nations (which the United States had never joined) to bury the doubting report, claiming it suffered from “contradictory and often insufficient premises”
⁸²
—and that was that. The international body never published it.
⁸³

Malariologists’ dispute over the antimalarial utility of mosquito killing rested on differing conceptions of the nature of mosquitoes’ carriage of malaria. Simply put, those who believed that all
Anopheles
mosquitoes carried malaria assumed that killing any
Anopheles
mosquitoes would help reduce malaria. Those who believed that something other than
Anopheles
mosquitoes carried malaria presumed that mosquito killing would do little to reduce malaria.

The truth was that neither side in the debate had it right: it wasn’t that all
Anopheles
carried malaria, or that something other than
Anopheles
carried malaria, but rather that
only some Anopheles
carried malaria. Research into the biology and mysterious habits of
Anopheles
mosquitoes would have revealed this fact, but both the skeptics and the enthusiasts had deflated funding interest with their conflicting orthodoxies. The American entomologist L. O. Howard, for example, tried to launch a research project on the identification of different species of
Anopheles
. But “there were many more species of mosquitoes than I had supposed,” with “infinite variations in habit,” he remembered. And “we could not possibly produce such a work as we wished to bring out” on the limited three-year grant Howard had scraped together. Funds to conduct this kind of mosquito research were so thin that the only way Howard figured he could continue the work at all was by dipping into the deep pockets of a fellow biologist.
⁸⁴

And so clues, when they appeared, arrived from obscure, unheralded corners.

First, in 1921, the French entomologist Emile Roubaud speculated that malaria transmission might be linked to some hidden quirk inside the
Anopheles
mosquito. Say, for example, that malaria-carrying
Anopheles
in some localities had more teeth, he theorized. They’d be able to bite through animals’ thick hides and therefore would deposit any malaria parasites within them into the dead-end host. Perhaps some other locality harbored mosquitoes with fewer teeth. Those insects would have no choice but to bite thin-skinned humans, and so could effectively carry malaria. The dental difference would explain why not all
Anopheles
species, such as the European
Anopheles maculipennis
, seemed to carry malaria.

Or say, as a retired public health inspector in Italy did in 1926, that the
Anopheles
mosquitoes that laid gray eggs carried malaria, while those that laid, say, dark eggs did not. The inspector, Domenico Falleroni, collected mosquito eggs as a hobby, and had noticed that individual female mosquitoes always laid eggs with the same markings. Finding the delicately designed eggs quite beautiful, Falleroni painstakingly described and categorized them, even naming two types
messeae
and
labranchiae
, after his friends from the health department Drs. Messea and Labranca.

Some scientists apparently conducted dental examinations of local mosquitoes and, finding nothing, dropped Roubaud’s idea. Falleroni’s ideas about the markings of eggs they dismissed as a “mere eccentricity of nature,” as biologically insignificant as “spots on mongrel puppies,” as the Rockefeller Foundation’s Lewis Hackett put it.
⁸⁵

It wasn’t until the late 1930s that a collaboration between Italian scientists and malariologists from the Rockefeller Foundation revealed that what had been inexpertly termed
Anopheles maculipennis
was in fact five different species of
Anopheles
mosquito, visually indistinguishable except for the delicate markings of their eggs. Of the five, only Falleroni’s
Anopheles messeae
and
Anopheles labranchiae
transmitted the scourge; the others were blameless.

•    •    •

This finding resolved the scientific impasse that had impeded widespread acceptance of the mosquito’s role in malaria for some forty years, decoding the mystery of millions of cases of European malaria.

Even more than that, it ushered in a new paradigm for malariology. Scientists realized that deciphering the ecology of malaria transmission required much more than simply checking the
Anopheles
credentials of the local mosquitoes. In Europe, delicate mosquito eggs had to be gathered and studied. In the United States, the two tiny hairs that protrude from mosquito larvae’s heads had to be examined—on harmless
Anopheles punctipennis
, those hairs are close together at the base; on the killer
Anopheles quadrimaculatus
, they’re spread ever so slightly apart.
⁸⁶

As the morphological differences between
Anopheles
species became clear, so did their unique habits, and the specificity with which each would have to be stalked within its own ecological niche. To stanch transmission, local entomologists had to work with engineers, who had to work with health officers and clinicians. For, as Lewis Hackett put it, “the best method in one place may be the worst possible thing to do only forty miles away.”
⁸⁷

Hackett summarized the new thinking in 1937:

A mosquito, harmless in Java, is found to be the chief vector in the interior of Sumatra. A method of treatment unusually successful in India is almost without effect in Sardinia. The half-mile radius, sufficient for larval control in Malaya, has to be quintupled in the Mediterranean basin. A village in Spain, in which half the population is in bed with chills and fevers in August, turns out to be less infected than a village in Africa where virtually no one has to abandon work on account of malaria at any time.
⁸⁸

Malaria, he said, was “so moulded and altered by local conditions that it becomes a thousand different diseases and epidemiological puzzles.”
⁸⁹
Each would have to be unraveled on its own terms.

•    •    •

It took malariology four decades to grasp the futility of single-bullet solutions to malaria. And yet, the paradigm-shifting insight described by Hackett has mostly been lost.

In part that’s because of the vagaries of malaria research funding. Local, ecologically driven malaria research is not particularly applicable to other areas of the economy, nor to other areas of the world. It must be funded locally for public health reasons alone, and political will or financial resources are lacking for it in most malaria-endemic regions. It’s challenging enough to fund proven treatment and prevention, let alone in-depth investigations into the entomology, ecology, and epidemiology of local malaria transmission. Even in wealthy countries, support for malariology ebbs and flows. When Italian authorities believed they’d solved their domestic malaria problem in the 1920s, for example, they dismantled their malaria research infrastructure altogether. When the United States and other international public health authorities believed DDT and chloroquine would end malaria, they similarly stopped funding research.

It’s also because, by the time Hackett’s revelation emerged, much of the infrastructure for malaria science had largely been built, and it suited locally grounded, ecologically minded malariology as well as a shoe fit a hand. None of the malaria research centers established by Patrick Manson, authorities in the British Raj, or the Rockefeller Foundation were sited in malaria-endemic regions, where malariologists could study malaria up close and on the ground. With the financial support of colonial authorities, Manson helped found the London School of Hygiene and Tropical Medicine in the malaria-free city of London.
⁹⁰
The Raj built malaria research institutes in India’s cool hill towns, which Britishers found more comfortable but where malaria seldom arose.
⁹¹
The Rockefeller Foundation poured dollars and the expertise of its malariologists into public
health research at American universities, such as Johns Hopkins and Harvard.
⁹²
These centers form the backbone of global malaria research to this day.