Pathogens and Disease

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.

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 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 (i.e. Kingston) 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.

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.

What is a Pathogen? Any microbes (organism or virus) that cause disease Including: Viruses Bacteria Fungi Protozoa Flatworms Roundworms

Viruses Considered Non-Living Two Parts: Function: Reproduction Ebola Considered Non-Living Two Parts: A Capsid: protein coat A Nucleic Acid: DNA or RNA Function: Reproduction Method: Hijack a living host cell and use it’s cellular machinery to replicate and build new virus particles. HIV

Virus Examples HIV: Human Immunodeficiency Virus Influenza Polio Ebola Herpes (different simplexes)

Staphylococcus aureus Bacteria Escherichia coli Staphylococcus aureus Most are not pathogenic All unicellular Parasitic strains and those that produce toxic byproducts are pathogenic

Bacteria Examples Streptococcus (Strep Throat) Escherichia coli Bacillus anthracis (Anthrax), Helicobacter pylori (causes peptic ulcers)

Fungi Decomposers that occasionally don’t wait until an organism is dead to feed on it Examples: Athletes Foot (skin) Most are surface/epidermal, some (rarely) become invasive

Protozoa Protozoa are unicellular Pathogenic examples include: vectors Giardia Many have insect vectors Giardia

Flatworms Many are parasitic Examples include: Tapeworms Flukes (liver fluke) Schistosoma

Roundworms Roundworms range in size from macroscopic to microscopic Many parasitic roundworms inhabit the intestines of a host organism Examples include: Pinworms like Enterobius vermicularis Hookworms like Necator and Ancylostoma Trichinella spiralis (larvae migrate to muscle)

Disease Transmission Direct Contact: Person to person – communicable (mononucleosis) Kissing Shaking hands Touching open wounds or sores Sexual contact – body fluids

Disease Transmission Indirect Contact: Objects – doorknobs, telephones, ect... Air (tuberculosis) Food (botulism) Water (typhoid fever) Vectors Animal Bites – disease to organism to humans (rabies, West Nile virus)

Disease Transmission Portals of Entry Respiratory Tract – nose, mouth, lungs Gastrointestingal Tract – throat, stomach, intestines Mucous Membranes – nose, eyes, etc. Penetration – bites, cuts, injections

Opportunistic Pathogens MDR TB and Staph Infections Malaria (hiding in liver cells) HIV attacking T-cells and rapid mutation Influenza and Rhinovirus rapid mutation rate (flu shots every year)

Prevention/Treatment Options Antibiotics Attack existing bacterial infections only Began with Penicillin (1928 – Fleming) Resistance observed rapidly Overuse, Incompletion of Prescription, Livestock application Vaccinations Prepare an immune system in advance of a viral (usually) or bacterial infection (i.e. tetanus) Dead or inactive parts of a pathogen or synthetic