Ch 10 - Infectious Diseases and Outbreak Investigation

epidemiologic transition

• stage 1

• stage 2

• stage 3

• stage 4

• stage 5

stage 1

• infectious and parasitic diseases

• accidents and animal attacks

• “natural checks” on population

stage 2

• receding pandemics

• sanitation, nutrition, medicine lead to lower CDR

• infectious diseases

stage 3

• degenerative and man-made diseases

• heart disease, cancer, diabetes, obesity

• chronic diseases

stage 4

• delayed degenerative disease

• extend life expectancy due to medical advances

• chronic diseases

stage 5

• potential resurgence of infectious disease due to globalization

epidemiological triangle

• agent

  • a factor (microorganism, chemical, radiation, mechanical, behavioral, social agent, process) whose presence, excessive presence, or absence is essential for a disease to occur

  • single agent, independent alternative agents (at least one must be present), complex of two or more factor (combined presence essential or contributes to outcome)

• host

  • a person or other organism providing subsistence/lodgment to an infectious agent in natural conditions

• environment

  • the domain in which disease-causing agents exist, survive, or originate, all that which is external to the individual human host

infection

• entry and development or multiplication of an infectious agent in the body of persons or animals

infectious disease

• a disease due to an infectious agent (bacteria, viruses, etc.)

communicable disease

• illness due to a specific infectious agent or its toxic products that arises through direct or indirect (a vector) transmission from an infected person, animal, reservoir to a susceptible host

contagious disease

• a disease transmitted by direct/ indirect contact with a host source of the pathogen

parasitic disease

• an infection cause by a parasite - an animal/vegetable/organism living on/in another and derives its nourishment thereform

infectious disease agents

• microbial agents such as bacteria, rickettsia, viruses, fungi, parasites, and prions

• vary in their infectivity (capacity to enter and multiply in a susceptible host and thus produce or disease)

• virulence = severity of the disease produced

• some agents enter the body, multiply, cause illness (direct)

• other agents produce a toxin, which causes illness

• toxin = a toxic substance (a material harmful to biologic systems) made by living organisms

• consequences include

  • subclinical and clinically apparent infections

  • zoonotic illnesses

  • foodborne illnesses

  • infectious disease outbreaks associated with specific occupations

  • infectious disease linked with water pollution

host (and immunity)

• hosts vary in their responses to disease agents

• immunity = host’s ability to resist infection through the presence of antibodies or cells having a specific action on the microorganism concerned with a particular infectious disease or on its toxin. low risk (with exceptions).

• susceptible hosts = those at risk (capable) of acquiring an infection

active immunity

• host has developed as a result of a natural infection with microbial agent

• acquired from vaccine (immunization) that contains an antigen (a substance that stimulates antibody formation)

• usually of long duration and is measured in years

passive immunity

• immunity acquired from antibodies produced by another person or animal

• newborn infants natural immunity conferred transplacentally from from its mother

• artificial immunity that is conferred by injections of antibodies contained in immune serums from animals or humans

herd immunity

• resistance (opposite of susceptibility) of an entire community to an infectious agent result of the immunity of a large proportion of individuals in that community to the agent

• limit epidemics in the population

clinical and subclinical disease

• clinically apparent disease

• incubation period

• subclinical (inapparent) infection

• generation time

clinically apparent disease

• produces observable clinical signs and symptoms

incubation period

• time interval between entry of infectious agent and the appearance of first sign/ symptom

subclinical (inapparent) infection

• does not show obvious clinical signs or symptoms

generation time

• time interval between entry of infectious agent

carrier

• person or animal “typhoid mary” harbors a specific infectious agent without discernible clinical disease serves as a potential source of infection

• when a carrier status is longstanding = a chronic carrier (the knick tv series)

index case

• the first case of a disease to come to the attention of authorities aka patient zero (typhoid mary mallon)

environment and infectious diseases

• physical

• climatologic

• biologic

• social/economic

endemic diseases

• endemic: when an agent causing disease is habitually present in an environment (either a geographic or population group)

• reservoir: a place where infectious agents normally live and multiply (human beings, animals, insects, soils, or plants)

• zoonosis: infection transmissible under natural conditions from vertebrate animals to humans (ie Rabies)

how infectious diseases are transmitted

• direct transmission

• indirect transmission

• significant infectious diseases

• zoonotic diseases

• emerging infectious diseases

• bioterrorism-related diseases

direct transmission

• direct and essentially immediate transfer of infectious agents to receptive portal of entry (respiration, wound, bite) through which human or animal infection may take place 

• ex: direct contact - touching, kissing, biting, sexual intercourse, projection (droplet spread) of droplet spray

indirect transmission (through intermediaries)

• vehicle (contaminated, nonmoving objects) borne infections

• airborne infections

• vector-borne infections

significant infectious diseases

• STDs

• foodborne diseases

• waterborne diseases

• bacterial conditions (e.g. cholera and typhoid fever)

• parasitic diseases (e.g. giardiasis and cryptosporidiosis)

• vector-borne (e.g. arthropod-borne) diseases

• vaccine-preventable diseases

• zoonotic diseases

• emerging infections

• bioterrorism-related diseases

zoonotic diseases

• rabies

• anthrax

• avian influenza (bird flu)

• hantavirus pulmonary syndrome rodents (deer mice)

• toxoplasmosis: a protozoal infection transmitted from cats feces

• tularemia (rabbit fever)

emerging infectious diseases

• infectious disease newly appeared in a population or that has been know for some time but is rapidly increasing in incidence or geographic range (ebola, e.coli, covid19)

bioterrorism-related diseases

• the deliberate release of viruses, bacteria, or other germs (agents) used to cause illness or death in people, animals, or plants

• these agents are typically found in nature but can be changed to increase their ability to cause disease, make them resistant to current medicines, or increase their ability to be spread into the environment