Though the climb is not technically as challenging as the Himalayas or Andes, the high elevation, low temperature, and occasional high winds can make Kilimanjaro a difficult trek. Acclimatization is required, and even experienced and physically fit trekkers may suffer some degree of altitude sickness. A study of people attempting to reach the summit of Kilimanjaro in July and August 2005 found that 61.3 percent succeeded and 77 percent experienced acute mountain sickness (AMS). A retrospective study of 917 persons who attempted to reach the summit via the Lemosho or Machame routes found that 70.4 percent experienced AMS, defined in this study to be headache, nausea, diarrhea, vomiting, or loss of appetite.