What particular diseases do I have to watch when I am trekking in Nepal?

Malaria is under control in Nepal. The risk of catching it is small and only in the southern plains. Mosquito netting and repellent are advised when there, especially during the summer and monsoon seasons. Also, as a preventive measure, take chloroquine pills starting two weeks before and six weeks after your visit to the plains of Chitwan or Bardia National Park. 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 travelled mainly by vehicles, the air gets a quite nasty especially during rush hour. Make a conscious effort to minimise your walking on these streets used mainly by vehicles during rush hour. Use the mask while you are walking in Kathmandu.