Travel and Infectious Disease

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Travel and Infectious Disease

Introduction

The global movement of infection is as old as the wanderings of mankind itself. A vast variety of bacteria, viruses, fungi, and parasites move on or in the bodies of humans, their clothing, belongings, pets, food, water, fleas, lice, and other fellow travelers. In fact, the widespread global presence of most infectious diseases reflects human travel dating to the earliest years of mankind itself.

History and Scientific Foundations

Travel-related infection has clearly changed world history for hundreds of years. The Black Death (plague) which began in Europe during the fourteenth century was caused by bacteria which infected rat-fleas introduced into Italy by ships. The “great pox” which affected Europe during the sixteenth century was caused by a new disease introduced by travelers from Africa, or possibly South America. The disease eventually evolved into modern day syphilis. Another pox disease that traveled in the opposite direction was instrumental in decimating Indian tribes in the New World during later years. In similar fashion, liver fluke and river blindness were introduced into Latin America as disease of slaves, but went on to adopt themselves to the local ecology, residing in insects or snails.

Although major diseases have crossed geographical borders for centuries, such events have only become commonplace in the twentieth century—as a result of widespread immigration, world conflict, and air travel. In earlier times, a disease characterized by an incubation period measured in days would appear, run its course (or kill the infected person) long before the human host could arrive to a far-off country by horse or schooner. Many will recall an outbreak of Ebola in Africa during 1995, when moviegoers and the world media debated a scenario in which an infected person travels to the United States and infects an unsuspecting population. The Ebola virus can remain in the human host for up to 21 days before onset of symptoms. The flight from Africa takes less than 12 hours.

WORDS TO KNOW

HOST: Organism that serves as the habitat for a parasite, or possibly for a symbiont. A host may provide nutrition to the parasite or symbiont, or simply a place in which to live.

PROPHYLAXIS: Treatment to prevent the onset or recurrence of disease.

VECTOR: Any agent, living or otherwise, that carries and transmits parasites and diseases. Also, an organism or chemical used to transport a gene into a new host cell.

Many infectious diseases are limited to specific regions, or even specific countries because of a requirement for specific plants, animals, insects, or climatic factors necessary for their propagation and survival. Others diseases are quite capable of adapting to new countries if introduced by man or his activities. Examples in recent years have included West Nile fever, which arrived to the United States in 1999, and quickly entered a favorable ecological environment consisting of compatible insects (mosquitoes) and birds (primarily crows). AIDS, which scientists suspect evolved into a human disease in Africa during the 1950s, exploded onto the world stage because largely because of universal air travel, injecting drug use, and sexual practices. More recently, SARS broke out of China when an infected physician visited Hong Kong, and when others went on to spread the disease to Canada, the Philippines, and other countries.

Impacts and Issues

As of 2000, many people would associate the word malaria with exotic jungles in far off lands. In fact, until the early twentieth century, malaria was quite common in North America and Europe. The mosquitoes that serve as vectors (transmitters) of this disease are still found in most developed countries, and an increasing number of small outbreaks in the United States and other malaria-free countries have followed introduction of the disease by an infected traveler. In fact, many cases of “airport malaria” infecting airport personnel and surrounding communities have been related to the presence of infected mosquitoes in the cargo holds of arriving aircraft.

Each year, billions of travelers cross international boundaries. The vast majority will not seek medical advice and will remain well. The most common medical problem will be traveler's diarrhea, affecting as many as 40 percent of tourists to some countries. Many medical problems are unrelated to infectious disease—automobile accidents, exposure to sun and high altitude, jet lag, petty crime, political instability. The chance of contracting malaria during a one-month tour varies from less than 1 per 1,000 (in southeast Asia) to over one percent (in sub-Saharan Africa). Many will be exposed to venereal disease, and a few will acquire AIDS. Rare instances of exotic and even life-threatening diseases such as yellow fever and African sleeping sickness are also acquired by tourists.

Since 1990, specialists expert in travel medicine have increasingly been involved in the prevention of all such problems. The pre-travel consultation consists of vaccination, prescription of prophylactic medications, and most importantly advice regarding medical risks and prevention. The informed tourist is a healthy tourist.