For centuries, human beings have spread diseases long distances through their travels. Yellow fever and the mosquitoes that transmit it, for instance, are thought to have originated in Africa and been introduced to the New World by slave ships in the 1500s.


The 1918 influenza pandemic illustrates how contagious diseases can spread throughout the world. More recently, West Nile virus, a mosquito-borne pathogen commonly found in Africa, West Asia, and the Middle East, has stricken people with serious illness in the United States, surfacing first in New York City.

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And let’s not forget about HIV, which is believed to be of African origin. HIV-associated nephropathy is a clinical entity seen with increasing frequency by nephrologists.


As global travel increases, it is likely American clinicians will see more exotic diseases in U.S. residents returning from abroad and in foreign visitors and immigrants. Already, malaria is diagnosed in about 1,300 people annually in the United States, according to the Centers for Disease Control and Prevention, and nearly all cases were acquired abroad in places where the disease is endemic.


Imported dengue is also diagnosed from time to time. From 1977 to 2004, more than 3,800 suspected cases of dengue—another mosquito-vectored viral illness—were reported in the United States among people who picked up the virus elsewhere.


Two articles in this issue underscore the potential for international travel and immigration to bring exotic diseases from faraway places to our doorstep. One report discusses the pros and cons of screening for solid organ donors for West Nile virus.


So far, two multiple-transplant recipients have acquired West Nile virus from an infected donor. In one case, the organ donor likely became infected through a blood transfusion, and in the other case, the source of donor infection probably was a mosquito bite. In the other article, an infectious disease specialist warns that the United States could experience a rise in the number of cases of urinary schistosomiasis, which is a common parasitic disease in sub-Saharan Africa and the Middle East.


In 2005, U.S. residents made 28,787,000 visits to overseas destinations and people abroad made 21,678,528 visits here, according to the U.S. Department of Commerce. With so much crisscrossing of the planet each year, it is just a matter of time before clinicians see the next surprise pathogen.