Malaria, and the
Panama CanalDavid McCullough
It was by considering the mosquitoes as predators more deadly than the most savage beasts of the jungle that Dr. Gorgas intended to solve the problem. Only by understanding the exact nature of the particular mosquitoes in question --- their reproductive processes, feeding habits, flight range, and so forth --- could he hope to destroy them.
Until the Cuban war comparatively little had been known about mosqultoes. It was not until 1895, for example, that a full account was published of even the common North American variety. The general impression was that all mosquitoes were more or less alike. At the time Reed and his co-workers identified Stegomyia fasciata as the yellow fever mosquito, no studies had ever been made of the insect's natural life history. So this too had been part of Gorgas' task at Havana and consequently he and his associates had discovered astonishing peculiarities that were of enormous value.
Seen under the microscope, Stegomyia is a creature of striking beauty. Its general color is dark gray, but the thorax is marked with a silvery-white lyre-shaped pattern; the abdomen is banded with silvery-white stripes and the six-jointed legs are striped alternately with black and pure white. Among mosquitoes Stegomyia is the height of elegance.
Stegomyia is also, like the rat, a creature of human society. It survives by maintaining a close proximity to human beings. As among all mosquitoes it is only the female that bites --- that is, only the female feeds on blood, while the male gets by on other liquids such as fruit juices and is quite harmless. For the female, blood is essential to mature her eggs. Though the female Stegomyia can feed on any warm-blooded animal, her decided preference is for human blood, and thus the whole life cycle of the insect must be maintained in close association with human society.
While all mosquitoes lay their eggs in water, the yellow-fever mosquito is extremely particular about where the water is located and its condition. The female Stegomyia will deposit her eggs only in or near a building occupied by human beings and only in water held in some sort of artificial container such as an earthenware jar or a rain barrel. In addition, it is essential that the water be clean.
With such information available, all acquired during the work at Havana, the problem of destroying the yellow-fever carrier became infinitely more manageable. "Men who achieve greatness," the brothers Mayo were to write in an essay about Gorgas, "do not work more complexly than the average man, but more simply....In dealing with complex problems, with the simplicity natural to him he went directly to the point, unaffected by the confusion of details in which a smaller man would have lost himself." At Havana the hopeless task of destroying all mosquitoes was reduced to destroying a particular mosquito; then, once the natural peculiarities of that species were recognized, it was possible to reduce the task further still. The campaign would center on the insect's method of propagation. The task, very simply, was to eliminate every possible opportunity for the female Stegomyia to deposit her eggs. Yellow fever was eradicated chiefly by ridding the city of all standing fresh water, or by sealing it off with wire screening or wooden lids, or with a skim of oil or kerosene, an idea first suggested for mosquito control in 1892 by the entomologist Leland O. Howard. (The oil not only discouraged the mosquito from depositing her eggs, but killed any larvæ already in the water, since the larvæ require air to survive.)
Thousands of adult mosquitoes had been destroyed in Havana by systematic fumigation of houses wherein yellow-fever cases had been found. Doors and windows had been sealed off with newspaper, room by room, and pans full of sulphur or powdered pyrethrum (a dried flower used as an insecticide) had been burned for an hour or more. But the main attack had been on water jars, barrels, cisterns, any stray bucket, tin can, or broken dish in which rainwater might collect. A card file had been made on every house and building within city limits; the city had been divided into sections and inspectors had been sent out daily to report on the Stegomyia-producing status of households within their districts. Water kept indoors for household use had to be covered. It had been a laborious, often thankless task, yet extremely simple in concept, and the results had been amazingly rapid.
The female Stegomyia lays anywhere from 35 to 120 minute black eggs and the maturation cycle from egg to larva to pupa to mosquito takes less than ten days. So with the campaign fully organized and in effect, Havana's Stegomyia population diminished quite suddenly. Adult mosquitoes died off, of fumigation or of old age, after three or four weeks, and because Stegomyia has an extremely limited flight range (another crucial characteristic discovered by Gorgas and his people), few replacements migrated into the city from outlying villages. It was thus that victory over yellow fever had come so quickly and decisively.
Anopheles, the malaria mosquitoes, were quite different creatures and thus a wholly different kind of problem. Anopheles, to begin with, are not purely house-bred insects. The female, unlike her Stegomyia counterpart, will deposit her eggs in still water of any kind --- any stagnant swamp, marsh, any clogged drain or ditch or mud puddle. Anopheles, therefore, are as much creatures of field or jungle as of the backyard. So while Stegomyia mosquitoes were always readily within range, their breeding grounds closely, neatly defined, Anopheles were literally everywhere, and in fantastic numbers, since the female deposits as many as two hundred eggs every ten days.
The sanitary measures taken at Havana --- the clearing away of garbage and refuse, the installation of proper drainage systems plus the campaign on Stegomyia's breeding grounds had the effect of giving no mosquito, Anopheles included, much chance to propagate within the city limits. But what chance would there be at Colón with its swamps or along the canal line?
Malaria, not yellow fever, Gorgas stressed to his associates, was the problem upon which their success would ride or fall. Malaria, he emphasized, had accounted for the greatest loss of life during the French years. "If we can control malaria, I feel very little anxiety about other diseases. If we do not control malaria our mortality is going to be heavy." Knowledge of the kind gathered at Havana on Stegomyia would now have to be gathered on Anopheles.
The initial question was which particular species of Anopheles to go after. "It was not known how many different species of Anopheles existed," wrote Joseph Le Prince, one of Gorgas' advance guard, "nor was it definitely known which of them were the important malaria carriers." To Le Prince, who had also been Gorgas' right hand at Havana, it was evident that "much investigative or pioneer work" was still called for.
We had no means of determining how seasonal changes would affect propagation, and the available data were unreliable. It was generally believed at that time that all mosquitoes traveled more or less with gentle air currents, but there was no positive knowledge of habits of flight, and the length of flight of Anopheles was yet to be determined. It was not known if or how topography affected the distribution of species, whether Anopheles larvæ thriving in small collections of water held by plants were of...importance, or whether certain species were confined to fixed geographical limits.
So while detailed information was being gathered and put on file concerning the whereabouts of Stegomyia larvæ in Panama City, Anopheles larvæ and pupæ were being carefully taken from puddles and swamps along the canal line, scooped up in white-enameled dippers, poured into wide-mouthed jars, and carried back to a makeshift laboratory at Ancon Hospital. Live adult Anopheles collected in villages along the railroad could not survive the return trip, it was found, unless carefully protected from direct sunlight, rain, and strong air currents --- an observation that was to have considerable subsequent value.
This preliminary survey disclosed the presence of Anopheles breeding grounds in or near every existing settlement, every abandoned camp built by the French. At a work camp at Culebra, a village of roughly five hundred Jamaicans, Gorgas found that every child he examined had a greatly enlarged spleen, a sign of chronic malarial infection. Every adult he talked to spoke of attacks of chills and fever within the preceding six months. On a hill above this same village a detachment of United States Marines was encamped, half of whom already had malaria. "The condition," he wrote, "is very much the same as if these four or five hundred natives had smallpox, and our Marines had never been vaccinated."
No one even tried to approximate the numbers of Anopheles present at any given point. Within the hospital compound itself their presence was phenomenal. On the panel of a single doorway one dutiful assistant counted fifty-four. Like Stegomyia, the Anopheles were easily recognized by their resting stance. In contrast to the common northern mosquito, which stands with proboscis and head crooked at right angles to its body, Stegomyia and Anopheles kept proboscis, head, and body on a straight line, but at an angle to the resting surface. When feeding on an arm or wrist, an Anopheles looked as though it were standing on its head.
To determine the time of day or night when the Anopheles would take blood, the men stretched out on cots in one of the wards, each man with a supply of pillboxes and a pocket watch. Every time a mosquito bit, or tried to, it was captured, put in a pillbox, and the date and hour were recorded on the box. The Anopheles, it was learned, would attack a human at rest at any hour, though the night hours were by far the worst. The life span of the insect seemed to be about a month and in that time the female required a meal of blood every two to three nights. Her bite did not cause any appreciable swelling, nor was the itch especially bothersome. Often a person was not even aware of being bitten by an Anopheles.
After a month or so, with only a few exceptions, all the small American force, Gorgas as well, had been down with malaria.
Time was the pressing concern. For although there were but one or two yellow-fever cases, and none serious, at the moment, that condition would change rapidly as soon as new human material became available for the Stegomyia fasciata --- and thus the disease --- to feed on. Gorgas' analogy to explain the violent wave effect of yellow fever --- the apparent absence of the disease followed by a sudden, vicious outbreak --- was the exhausted fire wherein concealed embers lay in wait for fresh supplies of fuel. The arrival of several thousand nonimmunes would be equivalent to heaping on dry kindling: nothing much would happen at first; then the disease would catch; the carrier mosquitoes would infect ever more victims with the deadly parasite, thereby creating more diseased blood for still more mosquitoes to feed upon. Unchecked, the disease would flare into a monstrous geometrical progression of death, taking hundreds, possibly thousands, of lives.
Were conditions on the Isthmus to remain as they were, and were upwards of twenty to thirty thousand men to be brought to Panama, as planned, then, Gorgas calculated, the annual death toll from yellow fever alone could run to three or four thousand.
The build-up of men and equipment was beginning. Every arriving steamer had its contingent of prospective carpenters, mechanics, file clerks, assistant engineers, all eager to be "in at the start at Panama." General Davis, who had been named the first Governor of the Canal Zone, and Chief Engineer Wallace had arrived and had taken up residence in Panama City. Gorgas, still working with the same small staff, tried to explain the situation, the need for immediate decisions, for men and supplies, and he got nowhere.
In August Admiral Walker and several of the commission came for an inspection tour and Gorgas again made his case as explicit as he knew how. The admiral and his party departed, weeks passed, nothing happened. Gorgas' cabled requests were answered evasively, if at all. Presently he was reminded by return cable that cables were costly and henceforth to use the mails.
The problem in essence was that Admiral Walker, Governor Davis, and several others on the Isthmian Canal Commission, as well as a very large part of the populace and its political leadership, did not seriously entertain the notion that mosquitoes could be the cause of yellow fever or malaria. To spend time and money chasing after mosquitoes in Panama would be to squander time and money in a most irresponsible fashion.
That the minds of men in such positions could be so closed in the face of all that had been learned and demonstrated in Cuba, not to mention the insistent warnings from Roosevelt and Welch, may seem inconceivable. In the conventional understanding of history, human advancement is marked by specific momentous steps: on December 17, 1903, at Kitty Hawk, the Wright brothers fly in a heavier-than-air machine and at once a new age dawns; in a hospital ward outside Havana Dr. Jesse Lazear dies a martyr's death and the baffling horror of yellow jack is at last resolved. But seldom does it happen that way. Ideas too have their period of extrinsic incubation, and particularly if they run contrary to what has always seemed common sense. In the case of the Wright brothers, it was five years after Kitty Hawk before the world accepted the idea that their machine could fly.--- From The Path Between the Seas
©1977 Simon & Schuster