Epidemiology Kept Simple Chapter 3 The Infectious Disease Process 1
Reasons to Study Infx D. Epi Infectious disease control, including emerging and reemerging agents Bioterrorism To illustrate general principals of epidemiology ( One Epi ) 2
What is Infection? Infection biologic agent living and replicating within host Contamination agent living on exterior surface of host Silent Infection infection without disease (commensal) Infectious disease infection accompanies by pathology Infection disease! Pathos 3
Components of the Infx Disease Process 1. Agent 2. Reservoir 3. Portals of entry and exit 4. Mode of transmission 5. Immunity 4
1. Agents Helminths (parasitic worms) Fungi & yeast (parasitic plants, lack chlorophyll) Protozoa (eucaryotes; complex life cycles) Bacteria (independent reproduction) Rickettsia (intracellular agents; require Ixodes tick carrier) Viruses (submicroscopic; incapable of multiplication outside of host) Prions (infectious proteins) 5
2. Reservoirs Reservoir where the agent multiplies and perpetuates Types of reservoirs Symptomatic cases Carriers Animals & insects Inanimate objects 6
Cases Reservoirs Some (not all) cases are contagious Examples of agents with case reservoirs Influenza Measles Smallpox Sexually transmitted diseases 7
Carrier Reservoirs Carrier contagious individual without discernable signs Types of carriers Inapparent throughout Incubatory Convalescent 8
Animals Reservoirs (Zoonoses) Human disease with an animal reservoir is called a zoonosis. Types of zoonoses Direct zoonosis: vertebrate animal human e.g., rabies Cyclozoonoses: species #1 species #2 human species #1 (e.g., Echinococcus tapeworm) 9
Types of Zoonoses (cont.) Metazoonoses vertebrate animal invertebrate human e.g., malaria Saprozoonoses vertebrate animal inanimate object human e.g. (coccidiomycosis) Valley fever 10
Water Food Soil Other Inanimate Reservoirs 11
Portals of Entry & Exit Respiratory Conjunctiva Urogenital Gastrointestinal Skin Placenta Etc. 12
Transmission by Contact Direct (host host) Indirect (host secretion host) Droplet (airborne, short distance) Nuclei (airborne, suspended) 13
Transmission via Intermediaries Vector (living) Vehicles (inanimate) Vectors types: mechanical, developmental, propagative, cyclopropagative. 14
Transmission Dynamics Common source Serial transmission 15
Transmission: Cycle in Nature Each agent has its unique cycle in nature Example: the blood worm (Shistosoma sp.). 16
Immunity Immunity all factors that alter likelihood and severity of infection after host is exposed Types of immunity (figure) 17
Innate Immunity Physical barriers: skin, cilia, mucosal, sheaths Chemical barriers: acidity, enzymatic, etc. Non-specific cellular & physiologic responses: phages, polymorphs, inflammation 18
Acquired Immunity Cellular (immunocytes) Lymphocytes Granulocytes Non-cellular (humoral) Antibodies Cytokines 19
Interaction of Innate & Acquired Immunity 20
Immunization Immunization the act of acquiring immunity Active immunization host response to exposure (Natural exposure or artificial vaccination) Passive immunization receipt of immunity products from others (Therapeutic e.g., anti-serums or maternal (transplacental, colostrum) 21
Types of Vaccines Killed vaccine: killed agent, not capable of self-replication Modified live vaccine: attenuated version of agent capable of replication Toxoid: denatured toxin (no agent) 22
Herd Immunity Non-susceptible individuals represented by dark circles. You do not need to vaccinate the entire herd to achieve control 23
Herd Immunity Animation http://www.immunisation.nhs.uk/about_im munisation/science/herd_immunity_- _animation 24