TRAVEL MEDICINE • CID 2001:33 (1 December) • 1887 TRAVEL MEDICINE INVITED ARTICLE Charles D. Ericsson and Robert Steffen, Section Editors Infections at High Altitude Buddha Basnyat, 1,2 Thomas A. Cumbo, 3 and Robert Edelman 4,5 1 Nepal International Clinic/Himalaya Rescue Association, Department of Human Physiology, Tribhuvan University, and 2 Patan Hospital, Kathmandu, Nepal; 3 Johns Hopkins University/Sinai Hospital of Baltimore Program in Internal, Medicine, 4 Division of Geographic Medicine, Department of Medicine, Division of Infectious Diseases and Tropical Pediatrics, Department of Pediatrics, and Travelers’ Health Clinic, University of Maryland Faculty Practice, and 5 Clinical Research, Center for Vaccine Development, University of Maryland School of Medicine, Baltimore Every year, thousands of outdoor trekkers worldwide visit high-altitude (12500 m) destinations. Although high-altitude areas per se do not harbor any specific agents, it is important to know the pathogens encountered in the mountains to be better able to help the ill sojourner at high altitude. These are the same pathogens prevalent in the surrounding lowlands, but various factors such as immunomodulation, hypoxia, physiological adaptation, and harsh environmental stressors at high altitude may enhance susceptibility to these pathogens. Against this background, various gastrointestinal, respiratory, der- matological, neurological, and other infections encountered at high altitude are discussed. Because there are few published data on infections at high altitude, this review is largely anecdotal and based on personal experience. In this review, we identify and discuss infections commonly encountered at high altitude. Because there are few published data on infections at altitude, this review is more anecdotal in nature and largely based on our personal experience. Although 2 of us (B.B. and T.A.C.) have medical experience in most popular mountain ranges, most of our time is spent in the Himalayas, and we emphasize the Himalayas in this report. This review is designed to serve as a guide for the counselors of people considering mountain travel, for health professionals treating infections in the field, and for those examining patients on return to base camp or to their home country. BACKGROUND High-altitude areas, defined here as 12500 m, do not harbor specific infectious agents per se. Pathogens encountered in the mountains (table 1) are also seen in the surrounding lowlands. High mountain ranges are distributed in diverse ecosystems, cover approximately one-fifth of the Earth’s surface, are home to 1300 million people, and are visited annually by tens of millions of persons who reside in lower elevations [1]. Many Received 12 February 2001; revised 14 August 2001; electronically published 19 October 2001. Reprints or correspondence: Dr. Buddha Basnyat, Nepal International Clinic, Laldurbar, GPO Box 3596, Kathmandu, Nepal (NIC@naxal.wlink.com.np). Clinical Infectious Diseases 2001; 33:1887–91  2001 by the Infectious Diseases Society of America. All rights reserved. 1058-4838/2001/3311-0014$03.00 ranges in developing countries attract travelers from developed countries who have had no previous exposure to the area’s indigenous pathogens. The traveler to high altitudes typically treks or climbs through several ecosystems en route, from trop- ical jungle or desert at the base of the climb to alpine and tundra zones at higher elevations. Theoretically, the dramatic physiological changes that occur during acclimatization [2] may modify innate defense mech- anisms against microbial infection, but there are few data that systematically examine such interactions. High-altitude envi- ronments pose stressors in the form of increased ultraviolet radiation, hypobaria, hypoxemia, hazardous weather condi- tions, inability to maintain adequate personal hygiene, cramped living arrangements, and isolation from adequate medical care. Theoretically, insect vectors and microbial pathogens them- selves may be affected by such environmental stressors, but except for the paucity of vector mosquitoes at higher altitudes, nothing is known about these possible interactions either. At high altitude, T lymphocyte function is mildly reduced, and defense against bacterial infection may be compromised, although resistance to viral infection is not affected and re- sponse to immunization is maintained [3]. Recent studies have shown changes in the immune system secondary to the pro- duction of immunomodulating compounds after exposure to increased concentrations of ultraviolet light [4]. Studies of gran- ulocyte function during physical exercise at high altitude de- scribe rapid reversal of granulocytosis after initial extravasation, and decreased production of superoxide anions [5]. In addition, Downloaded from https://academic.oup.com/cid/article/33/11/1887/445777 by guest on 09 March 2022