Also, as a preventive measure, take chloroquine pills starting two weeks before and six weeks after your visit to the plains. AIDS is a growing problem. Don't be misled into believing that unsafe sex is okay. Though prostitution in Nepal is insignificant compared to other Asian countries, watch out. Also, doctors in Kathmandu are reporting that health problems due to severe air pollution are rising astronomically in Kathmandu.
Old vehicles spewing out black smoke is unfortunately a normal scene on the roads of Kathmandu.
Along the main roads traveled mainly by vehicles, the air gets quite nasty especially during rush hour. Make a conscious effort to minimize your walking on these streets used mainly by vehicles during rush hour. Many, if not most, travelers to Nepal are likely to get stomach problems at some point during their visit. It is generally caused simply because of a change in diet and climate, drinking contaminated water and eating contaminated food. But if you do get it, the most effective remedy is to fast for a day and consume plenty of water or some fluid.