Infectious Diseases at High Altitude.

Travel to elevations above 2,500 m is an increasingly common activity undertaken by a diverse population of individuals. These may be trekkers, climbers, miners in high-altitude sites in South America, and more recently, soldiers deployed for high-altitude duty in remote areas of the world. What is also being increasingly recognized is the plight of the millions of pilgrims, many with comorbidities, who annually ascend to high-altitude sacred areas. There are also 400 million people who reside permanently in high mountain ranges, which cover one-fifth of the Earth's surface. Many of these high-altitude areas are in developing countries, for example, the Himalayan range in South Asia. Although high-altitude areas may not harbor any specific infectious disease agents, it is important to know about the pathogens encountered in the mountains to be better able to help both the ill sojourner and the native high-altitude dweller. Often the same pathogens prevalent in the surrounding lowlands are found at high altitude, but various factors such as immunomodulation, hypoxia, poor physiological adaptation, and harsh environmental stressors at high altitude may enhance susceptibility to these pathogens. Against this background, various gastrointestinal, respiratory, dermatological, neurological, and other infections encountered at high altitude are discussed.