How Mosquitoes & Microbes Changed The Course Of A Canal

The Panama Canal “was dug with a microscope”—only when yellow fever and malaria were eradicated, could its construction continue.

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AsianScientist (May 31, 2016) – A massive cargo ship glides in from the Pacific, the lock’s heavy steel gates swinging shut behind it. Up on the viewing platform, onlookers murmur restlessly—the ship sits idle, or so it appears.

But keep an eye on the water level, because there is a rumbling in the deep: valves are turning, and 100,000 cubic meters of freshwater rush in through holes in the chamber floor. The cavernous space will fill in a mere eight minutes, the rising water gently buoying ship and cargo up to the level in the next lock. The front gates open; the ship sails on, one step closer to the Atlantic.

I’m at the Panama Canal, watching metal and concrete move with a grace I didn’t think possible. The Canal’s locks raise vessels 26 meters above sea level to traverse the Isthmus of Panama—bypassing the long and dangerous journey around the South American continent—and lower them back down again on the other side.

Regarded as one of the greatest feats of engineering ever accomplished, this “aquatic staircase” moves almost 14,000 ships between the Atlantic and Pacific each year.

Man versus mosquito

I visited last month, while at a dengue conference in Panama City. For a gathering of experts on mosquito-borne diseases, you couldn’t ask for a more historically significant location—yellow fever and malaria famously plagued the construction of the Panama Canal, which began in 1880 under the French. Tens of thousands of workers were killed or sickened, playing a major role in France’s eventual abandonment of the project in 1889.

Yellow fever, with its high mortality rate and often gruesome symptoms, was particularly feared. The virus that causes the disease is related to dengue and Zika, but is far deadlier. While most people experience mild, flu-like symptoms, 15 percent of patients go on to develop severe disease: internal bleeding, vomiting, organ failure and jaundice (from which the disease gets its name). Of these, up to half die within ten days.

Even today, hospitalization and careful round-the-clock monitoring are the only treatment options; in the late 19th century, without advanced medical care, chances of survival were slim.

When the Americans took over in 1904, they realized that the Canal would never be built with yellow fever and malaria still rampant. Tasked with eradicating these diseases, chief sanitation officer William Gorgas set out on a mission to rid the Isthmus of mosquitoes and their breeding sites. Thousands of workers were sent out in “mosquito brigades” to systematically fumigate buildings and private homes, drain swamps, fill in stagnant water sources or cover them with kerosene, and clear away trash.

By this point, there was considerable scientific evidence that yellow fever and malaria were caused by mosquito-borne microorganisms. Yet, Canal officials still favored the prevailing “miasma theory”—the notion that the diseases were caused by toxic vapors from swamps, sewage, and urban filth in general. Gorgas’ mosquito control efforts—and their high price tag—were greeted with skepticism and ridicule.

David McCullough’s book The Path Between the Seas: The Creation of the Panama Canal, 1870-1914 details an argument between Gorgas and George Goethals, the Canal’s chief engineer, that illustrates this tension.

At one point, Goethals reportedly exclaimed in exasperation: “Do you know, Gorgas, that every mosquito you kill costs the United States Government ten dollars?”

“But just think,” Gorgas retorted, “one of those ten-dollar mosquitoes might bite you, and what a loss that would be to the country.”

The US government eventually granted Gorgas the resources he needed, and the results were dramatic—yellow fever was eradicated from the Isthmus by the end of 1906, and malaria kept at bay through the Canal’s completion in 1914.

Excavators, dredges, steam shovels, and dynamite, as it turned out, were not the only tools required to unite the oceans. What else?

“The Panama Canal,” goes a quote attributed to Ronald Ross, the British army doctor who first discovered the malaria parasite in the gut of a mosquito, “was dug with a microscope.”

Yellow fever today: an unwelcome return?

More than a hundred years after the first ship sailed through the completed Panama Canal, yellow fever still kills an estimated 60,000 people each year, mainly in Africa. An effective vaccine has been available since the 1930s, but in many countries is largely used as an emergency response rather than as a preventive measure.

Now, an ongoing outbreak in Angola has public health authorities worried about the disease’s potential to spread globally. Since December, when the outbreak began, people infected in Angola have brought the disease to Kenya, the Democratic Republic of Congo, Mauritania, and China. The global vaccine stockpile, already largely depleted after six million doses were dispatched to Angola, will be woefully inadequate in the event of a similar outbreak elsewhere.

The possibility of yellow fever spreading to Asia, where it has never been established, is particularly alarming: the region has plenty of the right mosquitoes (yellow fever is carried by the same species that transmit dengue, chikungunya, and Zika), as well as millions of non-immune people who would be at risk. Prevention would involve ramping up vaccine production, as well as vector control efforts.

Faced with such a scenario, ten dollars per mosquito now seems a small price to pay.

This article is from a monthly column called The Bug Report. Click here to see the other articles in this series.


Copyright: Asian Scientist Magazine; Photo: Sim Shuzhen.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Shuzhen received a PhD degree from the Johns Hopkins Bloomberg School of Public Health, USA, where she studied the immune response of mosquito vectors to dengue virus.

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