Introduction to Pathogens

What are pathogens? A pathogen is an infectious agent (“germ”) that causes disease or illness in a host. The host is the organism in which a parasite or pathogen does damage. Aside: Path- means suffering, -ogen means gives birth to.

What are pathogens? Examples of pathogens (which we will investigate more in our next lecture): Viruses (i.e. Rabies) Bacteria (i.e. E. Coli O157) Fungi (i.e. Athlete’s Foot Fungus) Protists (i.e. Trypanosoma) Prions Animal Parasites (i.e. Trichinella spiralis)

Key Terms Parasite Any organism that has a negative effect on another organism with which it has close contact. All pathogens are parasites.

Key Terms Pathogenesis The step by step development of a disease from infection by a pathogen to termination of either the germ or the host.

Key Terms Virulence (Potency) How well a pathogen causes disease. Usually inversely related to how well it spreads (see diagram on the right).

Key Terms Epidemiology It is the study of the factors affecting the health of populations. It serves as the basis for public health decisions and identifies risk factors for disease.

Key Terms Aetiology (Etiology) This is the study of what causes a disease. It is basically how scientists/doctors pinpoint what created the disease in order to better understand how to cure it or prevent it from spreading.

Key Terms Vector The item that transfers the pathogen to its host. Vectors are “vehicles” that transport pathogens from one host to another. Examples: water, blood, ticks, mosquitoes…

Key Terms Transmission The passing of disease from an infected individual to unaffected individuals. Passed by means of a vector.

Key Terms Endemic A common disease that occurs at a constant, but low, rate in a specific population. Example: Malaria in Liberia (Africa) is said to be endemic, as it is at a low rate, but constant enough that is it expected that the majority of the population will contract it at some point in their life.

Key Terms Epidemic When an endemic disease occurs more frequently than expected, in a given area over a given time period. Example: The flu would cause an epidemic if more than the usual number of people in a winter got the flu. Zika in South America?

Key Terms Pandemic It is an epidemic of infectious disease that has spread over a larger area (continent, worldwide…). Examples: HIV/AIDS since 1990, SARS and Avian Flu in the mid 2000s. Swine Flu in 2010.

Key Terms Eradication The reduction of a pathogen and its subsequent disease to zero. The only eradicated pathogen so far has been the smallpox virus. Other programs are underway to get rid of polio and the measles. Programs that have failed included ones to get rid of malaria, hookworm and yellow fever.