What animals bring diseases

By Isabella Storyclaire

last updated September 16, 2024

Contributions sourced from

How the Columbian Exchange Brought GlobalizationAnd Disease

Two hundred million years ago, when dinosaurs still roamed the Earth, all seven continents were united in a single massive supercontinent known as Pangaea. After they slowly broke apart and settled into the positions we know today, each continent developed independently from the others over millennia, including the evolution of different species of plants, animals and bacteria.

By 1492, the year Christopher Columbus first made landfall on an island in the Caribbean, the Americas had been almost completely isolated from the Old World (including Europe, Asia and Africa) for some 12,000 years, ever since the melting of sea ice in the Bering Strait erased the land route between Asia and the West coast of North America. But with Columbus arrivaland the waves of European exploration, conquest and settlement that followed, the process of global separation would be firmly reversed, with consequences that still reverberate today.

Why Do We Celebrate Columbus?

What Was the Columbian Exchange?

The historian Alfred Crosby first used the term Columbian Exchange in the 1970s to describe the massive interchange of people, animals, plants and diseases that took place between the Eastern and Western Hemispheres after Columbus arrival in the Americas.

On Columbus second voyage to the Caribbean in 1493, he brought 17 ships and more than 1,000 men to explore further and expand an earlier settlement on the island of Hispaniola (present-day Haiti and the Dominican Republic). In the holds of their ships were hundreds of domesticated animals including sheep, cows, goats, horses and pigsnone of which could be found in the Americas. (Horses had in fact originated in the Americas and spread to the Old World, but disappeared from their original homeland at some point after the land bridge disappeared, possibly due to disease or the arrival of human populations.)

The Europeans also brought seeds and plant cuttings to grow Old World crops such as wheat, barley, grapes and coffee in the fertile soil they found in the Americas. Staples eaten by indigenous people in America, such as maize (corn), potatoes and beans, as well as flavorful additions like tomatoes, cacao, chili peppers, peanuts, vanilla and pineapple, would soon flourish in Europe and spread throughout the Old World, revolutionizing the traditional diets in many countries.

Disease Spreads Among Indigenous Populations

The landing of Christopher Columbus at San Salvador in the Bahamas, 1492.

Along with the people, plants and animals of the Old World came their diseases. The pigs aboard Columbus ships in 1493 immediately spread swine flu, which sickened Columbus and other Europeans and proved deadly to the native Taino population on Hispaniola, who had no prior exposure to the virus. In a retrospective account written in 1542, Spanish historian Bartolom de las Casas reported that There was so much disease, death and misery, that innumerable fathers, mothers and children died Of the multitudes on this island [Hispaniola] in the year 1494, by 1506 it was thought there were but one third of them left.

Smallpox arrived on Hispaniola by 1519 and soon spread to mainland Central America and beyond. Along with measles, influenza, chickenpox, bubonic plague, typhus, scarlet fever, pneumonia and malaria, smallpox spelled disaster for Native Americans, who lacked immunity to such diseases. Although the exact impact of Old World diseases on the Indigenous populations of the Americas is impossible to know, historians have estimated that between 80 and 95 percent of them were decimated within the first 100-150 years after 1492.

The impact of disease on Native Americans, combined with the cultivation of lucrative cash crops such as sugarcane, tobacco and cotton in the Americas for export, would have another devastating consequence. To meet the demand for labor, European settlers would turn to the slave trade, which resulted in the forced migration of some 12.5 million Africans between the 16th and 19th centuries.

Syphilis and the Columbian Exchange

Photo 12/Universal Images Group/Getty Images

When it came to disease, the exchange was rather lopsidedbut at least one deadly disease appears to have made the trip from the Americas to Europe. The first known outbreak of venereal syphilis occurred in 1495, among the troops led by Frances King Charles VIII in an invasion of Naples; it soon spread across Europe. Syphilis is now treated effectively with penicillin, but in the late 15th-early 16th centuries, it caused symptoms such as genital ulcers, rashes, tumors, severe pain and dementia, and was often fatal.

According to one theory, the origins of syphilis in Europe can be traced to Columbus and his crew, who were believed to have acquired Treponema pallidum, the bacteria that cause syphilis, from natives of Hispaniola and carried it back to Europe, where some of them later joined Charles army.

A competing theory argues that syphilis existed in the Old World before the late 15th century, but had been lumped in with leprosy or other diseases with similar symptoms. Because syphilis is a sexually transmitted disease, theories involving its origins are always controversial, but more recent evidenceincluding a genetic link found between syphilis and a tropical disease known as yaws, found in a remote region of Guyanaappears to support the Columbian theory.

Smuggled animals may bring disease

Jan 21, 2005 (CIDRAP News) The next infectious disease to enter the United States might cross the border taped to a traveler's leg or tucked snugly under a tourist's hat.

Smuggling of wild animals has always posed hazards to human health, but the stakes may be getting higher today, given the role of animal hosts in lethal outbreaks such as SARS (severe acute respiratory syndrome) and avian influenza.

Any country can be one misstep away from an outbreak. Consider these cases:

When a Thai man landed at the Brussels airport Oct 18, 2004, customs agents found two rare eagles in plastic tubes in his suitcase. They looked relatively healthy, but tests showed both had H5N1 avian flu. No human cases of H5N1 were found as a result of the smuggling attempt.
Less than a month later, someone sneaked 28 parrots from Indonesia into Taiwan. Authorities euthanized the intercepted birds, which tested negative for the H5N1 virus, according to postings on the ProMED-mail Web site on Dec. 17, 2004.
In Malaysia, 30 chickens and quail were thought to have acquired H5N1 infections by consuming contaminated remains of infected fighting cocks smuggled from Thailand, according to a ProMED-mail posting on Sep 8, 2004.

The United States is vulnerable to the same threats. The nation bans the importation of animals thought to pose a disease risk (as well as animals that are legally protected because of their threatened status). Authorities acknowledge, however, that controlling illegal imports is a constant battle.

Moreover, import restrictions don't necessarily cover all the species that pose a threat. Scientists know that many dangerous infectious diseases are naturally carried by animal hosts, but they don't always know which animals carry disease.

When SARS was recognized in 2003, it didn't take long for investigators to learn that civets, used as food in southern China, carried the virus. But it wasn't until last fall that researchers identified domestic ducks as silent carriers of the H5N1 avian flu virus, about 7 years after the first human outbreak of H5N1 in Hong Kong in 1997. Thailand recently completed a study of wild birds and found that several species not previously known to carry the H5N1 virus were infected.

Import inspectors are fewThe United States relies on a network of agencies and a patchwork of rules to prevent illegal importation of wildlife.

The government has only 100 Fish and Wildlife Service (FWS) inspectors at ports of entry and 250 investigators nationwide. FWS, part of the Department of the Interior, also relies on other agencies to keep an eye out for smuggled creatures.

"We don't have wildlife inspectors at every port of entry," Sandy Cleva, an FWS law enforcement spokeswoman in Arlington, Va., told CIDRAP News. Instead, FWS collaborates with Customs and Border Protection (CBP) officers, part of the Department of Homeland Security, "so they would be alert to intercepting wildlife that's coming in illegally," she said.

"Customs has always lent a hand," Cleva added. Immigration and Customs Enforcement (ICE) officers often investigate related criminal activity.

The FWS's goals concerning wildlife imports are to protect threatened species and shield the nation from economic or ecological damage from imported pests, Cleva said. FWS also enforces the rules of other agencies, such as the Centers for Disease Control and Prevention (CDC).

CDC and other federal health agencies can ban trade in animals that pose a health threat. The agency banned the importation of African rodents in June 2003, civets in January 2004, and birds from eight Asian countries in February 2004. The US Department of Agriculture's (USDA's) Animal and Plant Health Inspection Service issued a similar order regarding Asian birds.

"We see enforcing these bans as a way to help our counterpart agencies and protect the American people," Cleva said.

Safety net is 'insufficient'Unfortunately, one CDC expert noted, bans often address only known threats without covering potential threats.

Monkeypox is a good example. Seventy-one people contracted monkeypox in 2003 after contact with prairie dogs used as pets. The prairie dogs had been exposed to Gambian giant rats imported from Africa, the CDC's Morbidity and Mortality Weekly Report noted on Jul 11, 2003. It was the first US outbreak of the disease.

"Prairie dogs aren't normally exposed to monkeypox," said Paul Arguin, MD, acting branch chief of the CDC's Geographic Medicine branch, which deals with travelers' health and imported zoonoses. "They ended up being a wonderful host for transmission."

In response to the outbreak, CDC banned domestic sales of prairie dogs as well as importation of African rodents. However, it's still legal to import many rodents from other countries, even though they could carry diseases new to the United States.

"I'd say the strategy in the past has been reacting in a very event-focused [way]," Arguin said. But he said the CDC is in the process of revising its animal import rules to include more comprehensive restrictions on high-risk animals.

For instance, small mammals in general pose a risk of carrying communicable diseases, according to Arguin. Although he couldn't specify when the rules would change, he said they will focus on prevention, within reason.

"It's a risk-benefit analysis," Arguin said. "To try to prevent all of the zoonotic disease, we'd have to close the doors. It's very hard to get to zero risk."

In addition to working on new rules, CDC recently increased its network of human quarantine stations from eight to eleven, adding sites in El Paso, Houston, and Washington, DC, Arguin noted. Staff duties may include monitoring the arrival of nonhuman primates. If CDC officials saw a possible disease risk in primates, they would call the USDA, which manages animal quarantines.

Arguin recommends strengthening the monitoring of legal and illegal importation through stronger partnerships, more staff, more ports, more inspections, and improved interagency information sharing.

"Our safety net needs to improve," Arguin said. "The monkeypox outbreak occurred. That is evidence our safety net is insufficient."

Smugglingan evolving gameNo matter how tough the import rules may get, smugglers will still dodge them. Ask Tamesha Woulard, FWS supervisory wildlife inspector in Chicago.

Woulard, who has inspected creatures as small as spiders and as large as a killer whale, likened wildlife smugglers to other criminals. "Are all drug dealers getting caught? Are all drunk drivers getting caught? They will always find ways to smuggle, then we'll adapt, then they'll find something new," she said.

The possibility of encountering sick animals makes education and safety paramount for inspectors, she said. A smelly, leaking container at an airport once turned out to contain bush meat. "You open it and see the bloody hands and arms of nonhuman primates," Woulard said.

She has added avian flu to her checklist of worrisome diseases, along with SARS and monkeypox.

"They're finding out this bird flu can transfer to mammals," Woulard said. (Cats, tigers, and leopards have contracted the flu.) "That puts [people] at risk even more."

Limiting the marketReducing illegal imports of animals that can cause human diseases may depend on reducing the market for imported wildlife through education. That task is part of the mission of Peter Knights, executive director of San Franciscobased Wild Aid, which tries to eliminate wildlife trade in the name of species protection and animal welfare.

Smuggling "seems an almost demonically designed mechanism to spread disease," said Knights. "The wildlife trader takes it from one remote place and ships it round the world."

He advocates campaigns to educate the public and echoes the call for improved enforcement.

Enforcement efforts, "if they exist at all, are totally underfunded," Knights said. He recommends that the United States focus on "obvious chokepoints," such as Senegal and Cameroon, creating teams of people on-site to stop animals before they are smuggled out of their homeland.

The stakes are high, he said. "The frightening thing with the bird stuff is it only takes one smuggled bird coming in to spark an outbreak."