Influenza occurs in the winter season in temperate areas and year-round in the tropics.
Tuberculosis has a worldwide distribution. Long-term travelers may want to consider getting a tuberculin skin test prior to departure and after returning. The BCG vaccine is of uncertain efficacy and is not recommended. For some diseases, there is no specific vaccine available. Insect precautions are recommended to reduce the risk of dengue fever, leishmaniasis, filariasis, Lyme disease, trypanosomiasis, and other arthropod-borne illnesses.