Explorers’ Diseases

This year, we learned just how quickly a disease can spread across a globalized world. But centuries before the travel time between Wuhan and Portland, Oregon shrank to just a few hours, diseases booked passage around the world on explorers’ ships and in their bodies. The infection rate may have been a little slower but it was no less devastating.

The Justinian Plague, which began in 541 AD, is considered the first pandemic in recorded history.


The Roman Empire brought some northern African diseases to Europe, and markets flourished with not just new, exotic goods, but also several types of flu and the bubonic plague. Between the fifteenth and eighteenth centuries, indigenous populations in the New World and Australasia, with no previous exposure to European diseases, died in uncountable numbers. Meanwhile, the explorers — vectors of illnesses that meant little to them but were fatal to those without antibodies — brought home the lasting gift of syphilis. For many explorers, illness was considered part of the hardships of the trail. The native peoples they met suffered in a less voluntary way.

Scurvy: the mariner’s curse

From the beginning of trans-oceanic exploration, dangers awaited even at sea. Long sailing voyages with poor hygiene, stale water and food from which certain subtle but essential nutrients had been lost, caused a tragic toll on ships’ crews.

The most feared ailment of all was scurvy, a debilitating disease that destroys the body’s connective tissue, causing lethargy, blotchy skin and rotting gums and teeth. Old wounds reopen; fractured bones re-break. If not treated, scurvy leads to death. Its mysterious cause was particularly frightening and confusing. It took an intellectual leap in the early twentieth century to consider it as an absence of something, in this case Vitamin C, rather than a poison found in foods or stale air.

Signs of severe scurvy have turned up in the skeletons of Christopher Columbus’s crew in what is now the Dominican Republic, on Columbus’s second trip.

The Scottish doctor James Lind was the first to administer citrus juices to combat scurvy among sailors.


From trial and error, but without understanding the disease, mariners eventually began carrying antiscorbutics such as lime juice on their voyages. Sometimes, even that was not enough. James Cook stocked sauerkraut, carrot marmalade and concentrated lemon and orange juice, and brought fresh fruits and vegetables on board as often as possible during stopovers, but scurvy eventually turned up among the crew. Read more about scurvy on long sea voyages here.

Other shipboard ailments included beriberi (lack of vitamin D), parasites and more serious diseases carried by rats.

Once on land, other dangers awaited, especially in the Tropics but also in the polar regions.

Arctic pitfalls

For arctic explorers, the situation on land was similar to onboard ship. Crews lacked fresh fruits and vegetables and didn’t realize that local Inuit took in vital missing nutrients by eating raw meat, which sailors would never deign to do. (Cooking destroys those fragile vitamin molecules.) So scurvy and beriberi remained a threat on land. Even when sailors had preventives like lime juice, they tried to shirk their daily doses, because they despised the taste. Often ship’s crews would assemble in the morning and drink their apportioned lime juice one by one, under the watchful eye of the bosun. The body can’t store Vitamin C very well, but it does hold a little, so scurvy usually flared up in late winter or early spring, after an arctic overwintering.

Sometimes, even when arctic explorers ate local meats, they did not understand that certain animals carried parasites like trichinosis, so eating fresh polar bear or walrus flesh was dangerous. Cooking killed the parasite, but the Inuit simply let the meat freeze for a while before eating it. Cold destroyed the parasite as well.

Polar Bear for dinner? Spare the liver. Photo: Wikimedia Commons


Equally dangerous was a problem caused not by lack of vitamins, but by an excess of one of them. Native peoples in the Arctic, who could hardly afford to be picky with food, never ate the livers of seals, dogs or especially polar bears. Toxically high levels of vitamin A are stored in these animals’ livers and can cause acute hypervitaminosis if eaten.


Meanwhile, in the Tropics…

In the Tropics, explorers became well-acquainted with fighting invisible –- or very tiny — enemies, especially mosquitoes and other insects. Malaria was already known in parts of Europe and North America, but the West African variety, caused by the parasite Plasmodium falciparum, was more aggressive. Not until the early 19th century did travelers begin to connect the disease with mosquitoes. In South America, so-called “Jesuit powder”, obtained from the bark of cinchona trees, became a medicine against malaria as early as the sixteenth century, when early missionaries saw Peruvian natives using it to treat fevers. Its active ingredient, quinine, served as an anti-malarial until after World War II — remarkable longevity for what was originally a folk cure.

Mosquitoes may also spread encephalitis, elephantiasis, dengue, West Nile virus, chikungunya, yellow fever, filariasis, tularemia, many forms of encephalitis, Ross River fever, Barmah Forest fever and nowadays, Zika. Little wonder that they are considered the world’s most dangerous animal.

Bark from the cinchona tree is rich in quinine.


Other illnesses come from airborne viruses and bacteria, such as the Treponema pertenue that causes yaws, spread mostly among children, or the Treponemoa pallidum, which causes syphilis. Today, syphilis is easily treated with penicillin, but in the colonial age, it was a terrible curse that could eventually affect the brain. The only remedy was arsenic, meant to kill the bacteria, hopefully before it killed the patient.

The catalogue of potentially lethal illnesses is enough to make any cautious traveler think twice about long tropical sojourns, but explorers were never the cautious type. One of the most famous explorers of the Victorian age, Dr. Livingstone, traveled from his native Glasgow to the banks of the Zambezi, to search for the elusive source of the Nile.

Livingstone had medical training but it was his wish to spread Christianity that took him to southern Africa in 1841. Although his religious mission was a failure — he never managed a single conversion — and his skills as expedition leader were so flawed that a member of one expedition wrote, “I can come to no other conclusion than that Dr L is out of his mind.”

Nevertheless, Livingstone’s resilience and force of will were remarkable, and he never stopped exploring until the many tropical diseases he contracted over the years ended his life at age 60.

Chromolithograph depicting one of David Livingstone’s expeditions.


The notes he left behind, documenting 30 years of African exploration, recount the multitude of ailments he was exposed to or witnessed, including cases identified nowadays as elephantiasis, hookworm, leprosy, yellow fever and many more. In 1858, his own wife succumbed to malaria in Central Africa.

Livingstone was the first to report that the tampan tick transmitted relapsing fever and that tsetse flies killed cattle with sleeping sickness, now called Trypanosomiasis. Like so many other diseases, it was not the biting creature itself but a parasite in it that was responsible. He didn’t witness the major outbreaks of sleeping sickness in the early 20th century, when colonialism forced people to inhabit tsetse fly-infested territories and affected, for example, one-third of the population of Uganda. But his observations drew attention to the role of insects, arthropods and parasites in the transmission of disease.

He also observed the relationship between malaria and mosquitoes and used quinine mixed with various ingredients to prevent it. Some of these medicaments he sold, in the style of the time, as “Dr. Livingstone Rouser’s Compound.” He himself suffered from malaria for most of his exploratory life, with at least 27 bouts documented.

A quinine and rhubarb compound, commercialized by Dr. Livingstone.

He also became familiar with helminth infections, such as the anemia caused by hookworms (Necator americanus). He recorded that a member of one expedition had “an insect in the eye”, probably a filarial worm known as Loa loa, which resides beneath the skin. But it was another helminth infection, bilharzia or schistosomiasis, that played a role in the doctor’s death. In his final days, Livingstone wrote: “I am pale, bloodless and weak from bleeding profusely… An artery gives off a permanent stream and takes away my strength.”

His symptoms also suggested dysentery, which he surely acquired from years of drinking putrid water. Although today there are effective treatments for bilharzia, nothing was available in Livingstone’s era.