A 19-year-old man presented to an emergency room in New Mexico in May of 1993 with an acute respiratory illness. The man was a marathon runner, previously in excellent health; his fiancée had died two days earlier with a severe respiratory illness. On exam, the patient was febrile, tachycardic, and tachypneic, but the rest of the physical exam was normal. The chest x-ray was clear, and laboratory findings were unremarkable. The patient was sent home on erythromycin and amantadine. Over the next two days the symptoms continued, and the patient developed vomiting and diarrhea. Repeat physical exams showed little change and clear lung fields. The next day the patient developed rapidly progressive shortness of breath and a cough productive of copious yellow sputum. Over several hours the patient developed fulminant respiratory failure and died.

This was the second person struck by the now famous Hantavirus pulmonary syndrome outbreak in the southwestern United States in the summer of 1993. The outbreak of the disease can be traced to unusual environmental conditions in the area. A rainy summer the previous year led to a large increase in the crop of piñon nuts; this in turn led to a rodent population explosion in the area. We now know that various species of rodents throughout the United States carry this strain of Hantavirus, and unrecognized cases among people may have occurred previously. The environmental factors that led to the increase in the reservoir population, and to inevitably closer contact between people and the rodents, resulted in the “emergence” of the disease at that time and place.

What may seem like subtle environmental changes can clearly have a significant impact on disease spread. The penetration of humans deep into tropical rainforests may bring people into contact with previously unknown diseases (HIV may have emerged in this way). Jet travel allows infected humans to spread disease rapidly around the world. Global warming may greatly expand the range of many vector populations, such as the Asian tiger mosquito, which was recently introduced into the United States in a shipment of wet automobile tires, and is now rapidly spreading throughout the southern United States. Finally, the enormous population density in many third-world cities provides a setting ripe for the rapid transmission of many diseases. All of these environmental factors are cause for concern about future outbreaks or epidemics of infectious disease.

Adapted from Duchin et al. (1994).

See also case study 17 in Appendix C.