Pathogens are any microorganisms that cause disease. These include viruses, bacteria, and parasites. They can spread via contaminated food and water; from one sick person to a healthy person; through contact with blood-containing pathogens; endogenous infection during an immunocompromised state.
Water- and food-borne pathogens are spread via uncooked meat, improperly washed fruits and vegetables, and unsanitary practices of food handlers.
Blood-borne pathogens are spread via vectors like mosquitos, and accidental injections of dirty syringes that were used on patients with hepatitis B or HIV.
A person can be immunocompromised when the patient is undergoing chemotherapy, chronic or prolonged use of corticosteroids, or if he or she is simply born with a weak immune system. In this state, the person can easily be infected with normally harmless bacteria that live inside of us.
