Viruses recognize no international borders or time zones.  They have no obligations to country, race, social status, or gender.  Rich and poor alike, are victims of viral infections which, if given the opportunity, may travel over extraordinarily long distances.  In 1983, the Asian tiger mosquito (the mosquito that transmits dengue fever virus) was found for the first time in the United States.  The mosquito larvae were transported on a cargo ship from Southeast Asia as stowaways in accumulated rainwater inside automobile tires.

In our modern world, viruses and other infectious microbes can easily hitch rides on international flights to and from any major city.  A tourist visiting Thailand can bring home a strain of human immunodeficiency virus from a sexual encounter in Bangkok.  A grandmother visiting her family in San Francisco following a stay in China can harbor a potent influenza virus in her lungs and pass it to her grandchildren who transmit it to other children in preschool.

We know viruses have been with us a long time.  Archeological evidence indicates smallpox developed along with civilization in the river basin agricultural settlements of Asia and the Middle East as early as 10,000 years ago.  We also know that most viral epidemic diseases were unheard of in the New World before the arrival of early settlers.  Viruses are not only the cause of many infectious diseases, ranging from the common cold to slow death of AIDS and the frightening fevers, but they have dramatically influenced history as well.  

Viruses have toppled dynasties, changed the outcomes of wars, and altered populations.  In the twentieth century, smallpox alone killed an estimated 300 million people.  In the sixteenth and seventeenth centuries small pox killed the emperors of Japan and Burma as well as many kings and queens of Europe.  The 1918-19 epidemic of Spanish influenza killed 33 million people in less than a year, causing more deaths than all the massive casualties of World War I.

Viruses not only infected humans but all living things including plants, animals, birds and sea creatures.  In 1999, seal plague virus killed 3,600 seals in the United Kingdom.  Canine distemper and other common animal viruses kill our pets as well as livestock.  Rinderpest, or cattle plague, killed an estimated 3 million cattle annually in South Africa during the 1930’s.  Viruses are everywhere, and due to their microscopic size they also infect the invisible world, including bacteria, fungi, and protozoa.