The Association of the British Pharmaceutical Industry states that four ways pathogens are spread are by droplet infection, direct contact, bodily fluids and vectors. Pathogens can also be spread via contaminated food and water.
Droplet infection refers to the spread of infection via tiny droplets of fluid that come out of the nose or mouth when someone sneezes or coughs. The droplets contain disease-causing microorganisms. The common cold is easily spread through droplet infection.
Direct contact occurs when an infected part of the body is touched by someone else. An example of this is the transmission of sexually transmitted diseases via genital contact.
Blood and semen are bodily fluids that can spread illness. If another person's blood gets into an open wound, it can spread diseases such as HIV.
A vector is an animal that spreads disease. The mosquito is a common vector that can spread malaria and the West Nile virus.