Some harmful bacteria can cause diseases like tetanus, salmonellosis, conjunctivitis, and sometimes pneumonia and tonsillitis. Viruses can also cause diseases in humans such as measles, chickenpox, the flu, colds, papilloma, and AIDS. Infectious diseases spread from person to person through the air or contaminated food or through mosquito bites in the case of malaria. Maintaining a healthy lifestyle includes eating nutritious meals, drinking water, getting exercise, sleeping enough, getting checkups and vaccinations, avoiding too much screen time and saying no to drugs.