• E-mail
• Print
• Comment
• Font Size
• Digg
• del.icio.us
• Discuss article

COMMENTARY - The Globalization of Human Pathogens

Posted on: Tuesday, 4 October 2005, 18:00 CDT

By Stanley M. Aronson

GLOBALIZATION, in the minds of many, is a recent phenomenon made notable by such happenings as the outsourcing of American jobs to India, the making of U.S. flags in China, the assembling of Toyota automobiles in Alabama, and the importing of professional basketball players from Serbia. These are indeed some of the many recent consequences of a global market economy that has surmounted many of the problems of transportation, communication, and tariffs.

The elements of globalization, however, were operative eons ago - - long before the word globalization, or indeed any word, had been contrived. Man migrated, step by step, from his arboreal home in the Rift Valley of Africa to Asia, Europe, the Americas, Australia, and, by boat, eventually to the remote islands of the Indian and Pacific oceans. Man himself was therefore the first globally exportable product in the burgeoning process euphemistically called civilization.

Humans populated such territories as Australia and the Americas, arriving via ancient land bridges that connected these regions to the Afro-Euro-Asian land mass. But subsequent climate change inundated the land bridges, resulting in the geographical and cultural isolation of human colonies.

Man the wanderer gradually evolved into man the seasonal nomad, and then into man the stable agronomist, forging a life for himself, his family, and his small clan. He became rooted in a small community, with its own language, customs, edible vegetation, and ecological risks and opportunities.

Each region had its distinctive predators, parasites, and pathogens -- all struggling to survive as each species learned to to coexist with the other occupants of their ecological niche.

Thus, man had to live with the botanical and zoological biota of his immediate environment. But as human colonies grew in number, as the number of people exceeded the local food supply, as trade developed, and as that curiously human trait adventurism emerged, some people left their sequestered settlements, both to occupy virgin soil and to seize the settlements of other groups.

As humans took to colonizing other regions, they brought with them their language, their foods, their customs, their domesticated animals, and their indigenous diseases, both parasitic and pathogenic. And so diseases that were once confined to isolated land masses were globalized.

Thus, the Spanish conquests of the Caribbean and what is now Latin America resulted in an unwelcome exchange of bacterial and viral pathogens. Syphilis, for example, had been previously confined to the Caribbean islands, as a relatively benign skin infection. But when it was brought to Europe by the sailors of Columbus, to a population immunologically unprepared for it, "the great pox" emerged as an often lethal disease. In turn, Spanish mariners and conquistadors brought smallpox, measles, and gonorrhea to the native populations of the Caribbean and Latin America, destroying much of those populations. Indeed, European invaders performed this role across most of the Western Hemisphere and the Pacific islands.

Infectious diseases spread among humans by physical contact (such as syphilis, gonorrhea, measles, and smallpox) or by airborne pathogens (such as influenza) tend to spread almost immediately after a carrier arrives amid a non-immune population.

And then there are the regional diseases that require an agent to transmit the pathogen -- an agent such as the mosquito. For these diseases to be transferred from one land mass to another, three things must coexist: a carrier of the disease; the appropriate species of female mosquito; and an immunologically susceptible human.

The rain forests of Africa are the assumed ancestral home of a number of mosquito-borne viral infections, including malaria, yellow fever, and dengue. The reservoir is probably the monkey.

It is not clear whether malaria existed in the Western Hemisphere before 1492. But it is certain that African slaves brought the malarial parasite with them, first to the Caribbean islands and then to the Western Hemisphere mainland. The lower holds of many slave ships also carried swarms of Anopheline mosquitoes, which then found tropical and subtropical lands in which to propagate.

Yellow fever was another pestilence uniquely African until the slave trade brought both the sufferers and the transmitting Aedes mosquito to the New World. The disease spread as far north as Philadelphia, devastating New Orleans and much of the rest of the lower Mississippi Valley, until the mosquito-abatement programs of the 1930s eradicated it.

Dengue (from the Spanish denguero and the Swahili denka), a viral disease, is now globally distributed, brought to each continent by slave ships and other commercial sailing vessels. Though not as serious as yellow fever, dengue is an evolving disease, with headache, excruciating muscle pains, fever, and a transient rash. There are about 100 million new cases of dengue worldwide each year, including about 77 Americans, who usually contract it when they travel in the Caribbean, the Pacific islands, or Southeast Asia.

Government leaders have warned Americans to accept the economic realities of globalization. Communicable diseases, heretofore confined to the tropics, are now another incontestable globalization reality.

Stanley M. Aronson, M.D., a weekly contributor, is dean of medicine emeritus at Brown University.

Source: Providence Journal

More News in this Category