The recent news of the rapid spread of the Zika virus in South America has reminded the world of the danger of mosquito-borne diseases, and of their destructive persistence. It was not always known how such diseases spread.
The potential for mosquitos to be intermediate transmission vectors may seem self-evident to us now, but this is only because we have the benefits of hindsight. For many centuries, the spread of malaria and yellow fever was cloaked in mystery and imprecise, and even ridiculous, conjecture.
All great discoveries, when seen in retrospect, can appear to be simple. Yet the great advances in scientific and medical knowledge are the result of painstaking labor, often taking place over many years of patient observation, testing, and analysis. What seems to be easy or simple may have been the result of years of focused intensity.
The career of Carlos Juan Finlay presents an illustrative example.
He was born Juan Carlos Finlay y de Barrés in Puerto Principe (now Camagüey), Cuba, in 1833. He had the good fortune of coming from a family wealthy enough to provide for his education, which was the best available to a Cuban lad of that era.
His father, who had been a physician himself and had fought with Simon Bolivar, sent the young Carlos to France for his education; but this was cut short in 1844 due to a bout with cholera. He recovered, and was sent back to Europe again, but this time he contracted typhoid fever, and was again forced to return to Cuba.
These traumatic experiences with disease must have played a major role in his determination to find ways of fighting infections.
He finally graduated from an American medical school in 1855, and opened a medical practice in Cuba in 1857. Further studies in Europe would follow, as any aspiring physician needed to acquaint himself with the most recent advances in the field.
Yellow fever in the nineteenth century was a terrifying disease. Known as the “saffron scourge,” it had existed in Africa for perhaps millennia, and came to the New World with the movement of goods and populations.
One writer described the disease in this way:
Yellow fever had a macabre way of toying with its victim before killing…For three days there was fever and chills followed by marked improvement. The temperature fell…He could think, if it pleased him to fantasize, that the worst was past. Maybe he could tell himself it had been influenza. Or perhaps a touch of malaria. Or some unnamed tropical thing, of which there were many. But on the fourth day yellow fever returned with a vengeance.
Beads of sweat popped out on the victim’s skin, as the fever returned and climbed steadily to 103, 104, 105…and then the chills came and the victim’s teeth chattered and he begged for covers…The end was near when tests detected that protein had begun to leak out of the blood, through the kidney membranes and into the urine…When the kidneys died, so did hope…If he was not so fortunate, consciousness faded into delirium and he screamed and cried out in his living nightmare until just before death, which usually occurred between the sixth and the ninth day. (Cf. Franklin, J & Sutherland, J.: Guinea-Pig Doctors: The Drama of Medical Research Through Self-Experimentation).
Even today, yellow fever continues to be a deadly affliction. Over one thousand cases are reported worldwide each year, but the true number, most of which are found in sub-Saharan Africa, has been estimated to be two hundred times greater. The first recorded cases in South America were noted around 1648 in Mexico, Cuba, and Barbados, and likely arrived as a byproduct of the slave trade. There were even outbreaks of the disease in North American cities, such as Boston, New York, and Philadelphia.
In the summer of 1793, for example, an estimated 5,000 people died of yellow fever in Philadelphia out of a total population of 60,000. Even George Washington himself was forced to shut down the government temporarily and retreat to Mount Vernon; he advised his staff to do the same. The disease continued to plague port cities all through the nineteenth century. Most vulnerable were those who lacked immunity to the disease (that came only with generations of exposure): travelers, immigrants, and those from cooler climates.
But how did the disease spread? And what caused it? No one really knew. Theories, of course, were legion. Malaria, a different disease but also one that seemed to go hand-in-hand with yellow fever, was believed to be caused by “bad air” (malus aer in Latin means “bad air”). Even in ancient times, the Romans learned to avoid swamps and marshes, due to the supposedly maleficent “air” that emanated from them.
The idea that an insect might be the source of a disease was never seriously proposed by anyone, as far as we know. Most nurses and doctors before Carlos Finlay’s time believed yellow fever was transmitted by contact with the linens or clothing of an infected person.
Finlay first proposed that yellow fever spread through mosquitos in 1881. How he precisely came to this conclusion is not entirely clear, but it appears that it was an inspiration born of direct, personal struggle. As we noted above, he suffered as a boy from cholera and typhoid; he also experienced yellow fever while in Philadelphia in 1853, and of course as a doctor in Cuba after he became a practicing physician in 1857.
There is no better catalyst for knowledge than the inferno of personal experience and uncompromising struggle.
Another researcher had demonstrated that the mosquito could act as a vector for disease, and perhaps Finlay was acquainted with his work. Patrick Manson had discovered in 1878 that mosquitos could infect other organisms with elephantiasis.
Finlay, although isolated in Cuba, was a brilliant thinker with a mind quick to seize on possibilities. He was fluent in French, German, English, and Latin, and had a consuming interest in all types of diseases. He would eventually write over forty articles on yellow fever alone.
He presented his theory (that the mosquito was the carrier of yellow fever) at an international conference in 1881. Reaction was generally positive, but conclusive experimental verification did not yet exist. For the next 19 years, Finlay conducted a series of 104 experimental trials in relative obscurity. Cuba was not a center of medical science, and he never received the recognition from the medical establishment that he deserved.
But he was determined, and he knew more about yellow fever than anyone else. Cuba suffered greatly from its ravages, and Finlay brought all of his insight and energy to solving the problem of its intermediary transmission.
Paradoxically, Finlay was unable to infect any of his test subjects with the disease using mosquitos. Yet he still persisted in his theory that mosquitos were the vector for the disease; he simply reasoned that he had ruled out all other possible causes. We now know that Finlay’s subjects were not infected simply because he (unfamiliar with the gestation period of the disease) did not wait enough time between the biting of an infected person and the biting of an uninfected person.
A renewed effort to deal with the disease came in the 1890s when it became clear that the United States would attempt to build a canal in Panama. A previous effort by France (through the de Lesseps Company) had been seriously impeded by the yellow fever epidemics that kept breaking out among the workers. Cuba would be a base of operations for the canal project.
In 1900, the United States sent a “Yellow Fever Commission” to Cuba to begin research on the disease, headed by an officer named Walter Reed. Even though Finlay’s ideas about mosquitos being the transmitter dated back to 1881, they were not generally accepted. Competing theories existed, and much time was wasted chasing down postulates that turned out to be dead ends.
Eventually, after much trial and error, and with the resources of the US government at his disposal, Reed conclusively confirmed Finlay’s hypothesis about the transmission of yellow fever, and gave him full credit for the discovery.
It was a moment of triumph not only for the advancement of learning, but also for the Cuban country doctor personally, who had been laboring alone for years with little, if any, recognition. Although he was nominated seven times for the Nobel Prize in medicine, he never received it.
And yet history acknowledges its debt to him every time medical inspiration is needed in an acute crisis, every time the imperturbable labors of the scholar dredge the silt of ignorance and inherited knowledge, and every time a grateful vessel passes through the Panama Canal, a glory of engineering that would hardly have been possible without his scientific insights.
He lit the torch that others would tend, and carry forward.
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