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Koch's Postulates

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1. The same pathogen is present in every case of the disease.
2. The pathogen must be isolated from the diseased host and grown in pure culture.
3. The pathogen from the pure culture must cause the disease when it is inoculated into
a healthy, susceptible lab animal.
4. The pathogen must be isolated from the inoculated animal and must be shown to be
the original organism.

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Symptoms

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subjective changes a patient experiences, e.g. malaise and pain

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Signs

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objective changes a physician can observe and measure e.g. fever

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Syndrome

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a specific group of symptoms or signs that always accompany a particular disease

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Communicable disease

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any disease that spreads from one host to another, either directly or indirectly. e.g. chickenpox, measles, genital herpes, typhoid fever, tuberculosis

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Contagious Disease

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disease that is easily spread from one person to another e.g. chicken pox

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non communicable disease

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any disease that is not spread from one host to another, e.g. tetanus

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Incidence

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the number of people in a population who develop a disease during a particular time period; indicates how easily the disease is spread

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Prevalence

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the number of people in a population who develop a disease at a specified time, regardless of when it first appeared; includes old and new cases

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Sporadic Disease

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– disease that occurs occasionally, e.g. typhoid fever in the USA

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Endemic Disease

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disease that is constantly present in a population e.g. common cold in the USA

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Epidemic Disease

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if a number of people in a given area acquire a certain disease in a relatively short time period, e.g. influenza in January in the USA

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Pandemic Disease

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an epidemic disease that occurs worldwide, e.g. influenza in 1918, AIDS now

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Acute Disease

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disease that develops rapidly and lasts a short time, e.g. influenza

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Chronic Disease

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disease that develops more slowly, but whose effects may be continual or recurrent, e.g. mononucleosis, tuberculosis, hepatitis B

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Subacute Disease

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disease that is intermediate between acute and chronic, e.g. subacute sclerosing panencephalitis

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Latent Disease

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disease in which the causative agent remains inactive for a time, but then is reactivated to produce symptoms of a disease, e.g. shingles

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Herd Immunity

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the presence of immunity in most of a population
The rate at which a disease spreads and the number of people affected are determined in part by the herd immunity. Vaccination can provide immunity to specific diseases. People who are immune to an infectious disease will not be carriers. They act as barriers to the spread of the disease

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Local Infection

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– the invading microbes are limited to a small area of the body, eg. abscess

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Systemic Infection

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– microbes and their products are spread throughout the body by the blood or lymph. e.g. measles

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Focal Infection

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agents of a local infection enter the blood or lymphatic system and spread to other areas of the body. e.g. gingivitis and tooth abscesses may result in infections of the heart valves or kidney.

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Primary Infection

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an acute infection that causes the initial illness

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Secondary Infection

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is a disease caused by an opportunistic pathogen after the primary infection has weakened the body’s defenses, e.g. Pneumocystis pneumonia in AIDS patients

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Subclinical infection

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an infection that does not cause any noticeable illness.
e.g. polio, hepatitis A in certain individuals

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Predisposing Factor

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factor or factors that make the body more susceptible to disease, e.g. gender, climate, age, fatigue, diabetes, malnutrition

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Incubation Period

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time between the intial infection and the onset of clinical signs/symptom

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Prodromal period

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early mild symptoms such as aches and malaise

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Period of Illness

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- clinical signs and symptoms are evident, an immune response is
mounted, the patient will either overcome the pathogen or the patient dies

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Period of Decline

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signs and symptoms of the disease subside; patient is vulnerable to
secondary infections.

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Period of Convalescence

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– person regains strength and returns to prediseased state. Recovery has occurred

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Reservoir

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continual source of the disease organism; it may be human, animal or non living

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Carrier

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people who harbor pathogens and transmit them to others without exhibiting any signs of the disease

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Zoonosis

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any disease that is transmissible from animals to man

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Animal Resevoirs

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exist for many zoonoses, e.g. skunks and bats harbor the Rabies virus
see Table 14.2 on pg. 432

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Nonliving Resevoirs

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– two major nonliving reservoirs are soil and water
e.g. soil harbors fungi that cause ringworm; Clostridium botulinum the bacterium that causes botulism and Clostridium tetani, the bacterium that causes tetanus.
Contaminated water is a reservoir for Vibrio cholerae which causes cholera and Salmonella typhi which causes typhoid fever.

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Three Routes of Transmission

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1. Contact. 2. Vehicle. 3. Vectors

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Contact 3 types

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Direct, Indirect, Droplet

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Vehicle types

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Waterborne, Food borne Airborn

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Vectors

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Mechanical, Biological

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Direct Transmission

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Person to person

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Indirect Transmission

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involves a nonliving object such as towels,
bedding, cups, silverware, toys

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Droplet Transmission

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microbes spread in droplet nuclei (coughing, laughing, sneezing, talking) that travel less than 1 meter from the reservoir to the host. Fig. 14.6 pg. 433

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Waterborne

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cholera, Shigellosis

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Foodborne

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tapeworms, food poisoning, e.g. that caused by Bacillus cereu

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Airborne

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spread of agents of infection by droplet nuclei in dust that travel more than 1 meter from the reservoir to the host
e.g. fungal spores in the transmisison of histoplasmosis

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Mechanical

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passive transport of the pathogen on a vector’s body part , e.g. a fly comes into contact with feces containing Shigella organisms, then lands on food at a picnic. People ingest the food and become ill with bacillary dysentery

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Biological

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active process that involves replication of the pathogen inside the vector prior to transfer to another host, e.g. rat flea and plague, mosquitoes and heartworms, mosquitoes and malaria

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Fomite

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any nonliving object involved in the spread of an infection

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Vectors

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animals that carry pathogens from one host to another Table 14.3

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What is the 8th leading Cause of Death

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NOsocomial Infections

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1940s and 1950s

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most nosocomial infections were caused by G+ microbes including Staphylococcus aureus

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1970s

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gram-negative bacilli, Escherichia coli and Pseudomonas aeruginosa

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1980's

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antibiotic resistant gram-positive bacteria, Staphylococcus aureus and Enterococcus spp

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1990s

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34% of the nosocomial infections are due to Staphylococcus aureus and Enterococcus spp.
32% of the nosocomial infections are due to Escherichia coli and Pseudomonas aeruginosa

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What are most nosocomial infections?

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Urinary Tract Infections

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20% of Noscomial infecitons

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Surgical Site infections

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Compromised Host

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one whose resistance to infection is impaired by disease, therapy, or burns

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Emerging Infectious Diseases

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diseases that are new or changing, showing an increase in incidence in the recent past, or a potential to increase in the near future. Table 14.6 pg. 439-440

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Epidimology

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the science that studies when and where diseases occur and how they are transmitted in populations

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There are 3 types of investigations that can be used to analyze the occurrence of a disease

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descriptive, analytical and experimental.

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Case Reporting

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procedure that requires health care workers to report specified diseases to local, state and national health officials. Table 14-7 pg. 430
e.g. AIDS, measles, polio, gonorrhea, tetanus, typhoid fever, tuberculosis

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CDC

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The Centers for Disease Control and Prevention in Atlanta, GA.
This is a branch of the US Public Health Service
The source of epidemiological information in the USA

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Morbidity

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the number of people who have a specific disease

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Mortality

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the number of deaths due to a specific disease

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MOrbidity rate

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the number of people with the disease
total population exposed to the disease

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Mortality Rate

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he number of people who died from a disease
the number of people who were ill from the disease

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