• HIV/AIDS—This disease apparently emerged in central Africa in the 1950s or earlier ¹ and spread through most of Africa, Asia, Europe, and the Americas during the 1970s and 1980s. Because the AIDS virus weakens an individual’s immune defenses, an individual with HIV/AIDS may become coinfected with malaria, tuberculosis (TB), or pathogens that cause diarrhea or pneumonia.

• TB—During the 1980s, this age-old scourge, which had been nearly eliminated in the West by antibiotic treatment, reemerged—sometimes in a multidrug-resistant form—in cities around the world, including in the United States. By 2000, approximately 46% of newly identified U.S. TB cases originated in other countries.

The spread of TB has been hastened by lack of public health surveillance for this disease and by the concurrent HIV/AIDS epidemic.

• Malaria—Although malaria was eliminated in the United States as an endemic disease by the 1960s (through swamp-draining and vector control programs), approximately 1,500 cases of malaria are reported in the United States each year. One-half occur in U.S. travelers to malaria-endemic countries and the other half occur among foreign nationals who enter the United States already infected.

Over the past 15 years, more than 80 people in the United States were infected by local transmission within our borders. In other countries, the spread of malaria has been augmented by the spread of antimalarial drug resistance, and many parasite strains are increasingly resistant to preventive antimalarial drugs taken by travelers.

• West Nile encephalitis—This mosquitoborne viral disease carried by migratory birds in Asia, Africa, and Europe, caused 79 cases of encephalitis and 7 deaths in the northeastern United States in 1999.

Because the West Nile virus had never before been detected in the Americas—and because it had been mentioned by an Iraqi defector as an organism of interest to the Iraqi bioweapons program—it was speculated that a strain of West Nile virus isolated in New York City might have been deliberately engineered and disseminated to harm U.S. citizens. However, the scientific evidence suggests that the outbreak was caused by a naturally occurring viral strain. ²

Map of the Americas showing cholera outbreaks Geographic extent of the Latin American cholera epidemic over time, since its beginning in January 1991. Lines represent the advancing front of the epidemic at different times. Since 1995, most Latin American countries have reported diminishing numbers of cases. Cholera has not yet reached the Caribbean. Adapted from: Tauxe RV, Mintz ED, Quick RE. Epidemic cholera in the New World: translating field epidemiology into new prevention strategies. Emerging Infectious Diseases 1:141-6, 1995.

• Vibrio cholerae O1, El Tor biotype—A virulent strain of cholera has caused an ongoing pandemic that has lasted 40 years and affected more than 75 countries.

Beginning in 1961, Vibrio cholerae O1, El Tor biotype spread from Indonesia through most of Asia into eastern Europe and Africa. From North Africa it spread to the Iberian Peninsula and into Italy in 1973. In the late 1970s, small outbreaks occurred in Japan and in the South Pacific.

In January, 1991, epidemic cholera appeared in Peru and spread rapidly through most of Latin America, causing over 1,000,000 cases by 1994. This was the first time in 100 years that a cholera pandemic had reached the New World.

• Salmonellosis—A multistate outbreak carried by contaminated mangoes grown in Brazil caused 79 cases of Salmonella Newport infections in 13 states in 1999.

The outbreak was detected and investigated using PulseNet, the U.S. early warning system for foodborne diseases (see Priority 2: Objectives). PulseNet linked 78 cases in 22 states by comparing the molecular fingerprints of the isolates. Once mangoes were implicated as the common exposure for these cases, FDA traced the source of the mangoes back to a single farm in Brazil. The mangoes had been dipped in warm water in a new process designed to kill fruit-fly larvae before exportation. Unfortunately, the processing water may have been contaminated with Salmonella.

• Coccidioidomycosis—Outbreaks caused by Coccidioides immitis, a soil-dwelling fungus common in arid and semiarid parts of the Western Hemisphere, were reported in 1996 in Washington State and in 2000 in Pennsylvania.

The outbreaks occurred among church mission groups who visited endemic regions of northern Mexico to undertake construction projects. Infected individuals experienced a severe influenzalike disease with fever, chills and cough. Fungal disease was not initially suspected.

• Influenza spread on cruise ships—A 1997 outbreak of the A/Sydney strain of influenza occurred among people on a cruise that made stops in Canada and New England.

The A/Sydney strain had been isolated in Australia too late in the year to be included in the vaccine formulated for the fall/winter flu season in the Northern Hemisphere. Therefore, the cruise ship passengers had not been immunized against it.

• Measles—Fifty-six of the 87 cases of measles identified in the United States in 2000 were traced to importations of the virus from outside our borders. Twenty-six were direct importations, 18 were secondary cases, and 8 involved viruses whose DNA sequences suggested a foreign origin.

Comprehensive surveillance and genetic sequencing of all identified strains of the virus allow for tracing of the outbreak strains to the country of origin. The finding that indigenous measles transmission can be interrupted in the United States is an important impetus for supporting a global measles elimination campaign.

• Polio—Eliminated from the Western Hemisphere since 1991, paralytic polio was again identified in Haiti and the Dominican Republic in 2000, and attributed to waning immunization coverage rates in those countries.

Unless immunization coverage can be strengthened in other neighboring countries, diseases thought no longer to be a risk for U.S. children may be imported by travelers.