Epidemiology: Practical Disease Concepts

TEST 5/13 (TUESDAY)

What is etiology?

the study of causes of disease and their mode of operation

Remember the difference between communicable & non-communicable diseases:

• Communicable: Infectious Disease

• Non-Communicable: Chronic Disease

What is the definition of acute?

relatively severe disorder with sudden onset and short duration of symptoms

What is the definition of chronic?

less severe but continuous duration, lasting over long periods, if not a lifetime

What is the agent?

the cause of disease

What is the host?

a human or animal that is susceptible to the disease

What is a vehicle (fomite)?

a nonliving intermediate such as clothing, food, or water that conveys the infectious agent from its reservoir to a susceptible host

What is a carrier?

contains, spreads or harbors an infectious organism

• can be asymptomatic

What is viability?

the capacity of the pathogen to survive outside the host and to exist or thrive in the environment

What is a zoonotic disease?

disease that can be passed from vertebrate animals to humans or vice versa

Who is patient zero?

refers to a person identified to be the first carrier of a communicable disease in an outbreak of related cases

What is vertical transmission?

Transmission from an individual to their offspring through sperm, placenta, milk, or vaginal fluids

What is horizontal transmission?

Transmission from an individual to a susceptible contemporary. This can involve direct transmission (STDs), a common vehicle (water-borne, food-borne, or blood-borne diseases), airborne pathogens (like tuberculosis), or vector borne pathogens (like malaria)

What is direct transmission?

immediate transfer of an infectious agent from one person to another

What is indirect transmission?

→ an agent is transferred by an intermediate item, organism, means, or process to a host, resulting in disease

• Airborne: when droplets or dust particles carry pathogens to a host

• Vector-borne: when an arthropod (mosquito, flee, etc.) conveys the infectious agent

• Vehicle-borne: an inanimate object (such as water) that conveys an infectious agent to a host

What are the stages of disease?

1. Stage of Susceptibility

2. Stage of Presymptomatic Disease

   1. Incubation Period: The time period between an infection by a pathogen and the first symptoms of disease 

   2. Latency Period: the time when a disease is present but not symptomatic or detected

3. Clinical Disease

4. Stage of Recovery, Disability, or Death

How is disease classified?

• Congenital and Hereditary: structural or functional anomalies that occur during intrauterine life. 6% of babies are born with congenital anomalies

• Allergies and Inflammatory Diseases: Allergies are a hypersensitivity of immune system to typically harmless substances in the environment. Inflammation is a biological response of the body to a harmful stimuli such as pathogens, damaged cells, or irritants.

• Degenerative Diseases: disease in which function or structure of the affected or organs changes for the worse over time. It is often associated with the aging process but it may not be age related.

• Metabolic Disease: when abnormal chemical reactions in your body disrupt the ability to process and break down food for energy

• Cancer: a group of many diseases characterized by uncontrolled cell growth or the loss of a cell’s ability to perform apoptosis

What are reportable diseases?

• The WHO provides a list of internationally recognized diagnostic classifications for general epidemiologic and health management purposes, called the ICD (International Classification of Disease). 

• The WHO uses death certificates, hospital records, and other sources to compare statistics among member states.

• The CDC also has a national reporting system. It is not mandatory to report nationally but it is mandatory to report to the state. Each state has different requirements. The requirements also change year to year to reflect the emergence of new pathogens or the decline in incidence of certain diseases

What is needed for a disease to be on a state’s list?

1. Causes serious morbidity or death

2. Has the potential to spread

3. Can be controlled with appropriate intervention

What is the difference between endemic, epidemic, & pandemic?

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What is primary prevention?

• preventing a disease or disorder before it happens. Health promotion, health education, and health protection are primary prevention.

• Active requires behavior change of the individual

  • Ex. begin exercising, stop smoking, immunizations, etc.

• Passive primary does not require behavior change

  • Ex. eating vitamin-enriched foods, drinking fluoridated water)

What is secondary prevention?

aimed at health screening and detection to identify disease

What is tertiary prevention?

limiting disabilities by providing rehabilitation when a disease, injury, or disorder has already occurred and caused damage

How do vaccines work?

• imitating an infection to engage the body’s natural defenses

• A single dose of vaccine only provides partial immunity

• Live attenuated vaccines give more protection than non-live attenuated vaccines, however, all of them usually require multiple doses and/or a booster to restore protection

What is the difference between an antibody and antigen?

• All vaccines have an active ingredient called an antigen. An antigen is a substance that causes the immune system to begin producing antibodies

• Antibodies are proteins produced by white blood cells to identify and neutralize foreign substances. 

The antigen is either: 

• Weakened or killed virus or bacteria

• Bits of the exterior surface or genetic material of a virus or bacteria

• Bacterial toxin treated to make it non-toxic

Explain the difference between live attenuated and non-live attenuated immunizations:

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Explain the difference between active & passive immunity:

Active - exposed to disease whether naturally or vaccine-induced 

• *Active immunity takes longer to build but lasts longer

Passive - provided from another human or animal

• Ex. babies are passed antibodies from their mother during the final months of pregnancy

• immediate but fades quicker

What is herd immunity?

The notion that if the herd (a population or group) is mostly protected from a disease by immunity, the chance that a major epidemic will occur is limited. Herd immunity provides barriers to prevent direct transmission through a population