Chapter 14 Principles of Disease and Epidemiology Lectures prepared by Christine L. Case © 2013 Pearson Education, Inc.

Introduction Pathogens- disease causing organisms Our defenses either resist the pathogens or they can get into our body and cause temporary or permanent damage

Pathology, Infection, and Disease Pathology: the study of disease Etiology: the study of the cause of a disease Pathogenesis: the development of disease Infection: colonization of the body by pathogens Disease: an abnormal state in which the body is not functioning normally

Normal Microbiota and the Host Humans are generally free of microbes while in the uterus At birth, microorganisms begin to establish themselves on our bodies. Normal microbiota- permanently colonize the host Transient microbiota- may be present for days, weeks, or months Symbiosis- is the relationship between normal microbiota and the host

Many factors determine Normal Microbiota distrubution: Nutrients Physical and chemical factors- pH, temp Host defenses Mechanical factors- chewing, urine flow Host conditions- age, diet, emotional state

Figure 14.1 Representative normal microbiota for different regions of the body. Bacteria (orange spheres) on the surface of the nasal epithelium Bacteria (brown) on the lining of the stomach Bacteria (orange) in the small intestine

Symbiosis- the relationship is needed by at least one of the organism Commensalism- one organism benefits, and the other is unaffected Mutualism- both organisms benefit Parasitism- one organism benefits at the expense of the other Opportunistic pathogens- usually don’t cause disease in a healthy person when they are in their normal habitat but do when they get moved AIDS pt. becoming infected with Pneumocystis jirovecii

Normal Microbiota and the Host Microbial antagonism is a competition between microbes Normal microbiota protect the host by Occupying niches that pathogens might occupy Producing acids Producing bacteriocins Probiotics: live microbes applied to or ingested into the body, intended to exert a beneficial effect

Normal Microbiota by Body Region Skin- Propionibacterium, Staphylococcus sp., Candida Nose and Throat- Staphylococcus aureus and epidermidis, Streptococcus sp., Neisseria Mouth- Candida sp. Large Intestine- Escherichia coli, Proteus sp., Klebsiella sp., Clostridium difficile Urinary and Reproductive Tracts- Pseudomonas sp., Klebsiella sp., Proteus sp., Candida albicans

Table 14.1 Normal Microbiota on the Human Body Eyes (conjunctiva) Nose and throat (upper respiratory system) Mouth Skin Large intestine Urinary and reproductive systems (lower urethra in both sexes and vagina in females)

Koch’s Postulates The same pathogen must be present in every case of the disease. The pathogen must be isolated from the diseased host and grown in pure culture. The pathogen from the pure culture must cause the disease when it is inoculated into a healthy, susceptible laboratory animal. The pathogen must be isolated from the inoculated animal and must be shown to be the original organism.

Figure 14.3 Koch’s Postulates: Understanding Disease. Microorganisms are isolated from a diseased or dead animal. The microorganisms are grown in pure culture. 3 The microorganisms are injected into a healthy laboratory animal. 1 2a Colony The microorganisms are identified. 2b 4 Disease is reproduced in a laboratory animal. 5a The microorganisms are isolated from this animal and grown in pure culture. Microorganisms are identified. 5b The microorganism from the diseased host caused the same disease in a laboratory host.

Koch’s Postulates Organisms and their specific diseases: Bacillus anthracis- anthrax Mycobacterium tuberculosis- TB Koch’s postulates are used to prove the cause of an infectious disease

Exceptions Some microorganisms can only be grown in humans. This leads to ethical questions. HIV Some diseases all cause the same type of symptoms. Can be hard to distinguish. Some organisms require specific environments to grow Treponema pallidum can’t grow on an ARTIFICIAL media. These organisms have to be grown using live specimens such as rats, guinea pigs, birds.

Classifying Infectious Diseases Symptom: a change in body function that is felt by a patient as a result of disease Sign: a change in a body that can be measured or observed as a result of disease Syndrome: a specific group of signs and symptoms that accompany a disease

Classifying Infectious Diseases Communicable disease: a disease that is spread from one host to another Genital herpes, Chicken Pox Contagious disease: a disease that is easily spread from one host to another Chicken Pox Noncommunicable disease: a disease that is not transmitted from one host to another Tetanus

Occurrence of a Disease Incidence: fraction of a population that contracts a disease during a specific time; new cases HIV cases in US 2007- 56,300 Prevalence: fraction of a population having a specific disease at a given time; looks at old and new cases HIV cases in the world in 2007- 1,185,000 Sporadic disease: disease that occurs occasionally in a population

Occurrence of a Disease Endemic disease: disease constantly present in a population Colds Epidemic disease: disease acquired by many hosts in a given area in a short time Flu Pandemic disease: worldwide epidemic AIDS

Severity or Duration of a Disease Acute disease: symptoms develop rapidly; usually short lived Stomach virus, Flu Chronic disease: disease develops slowly; usually long TB, Hepatitis B, Mononucleosis Subacute disease: symptoms between acute and chronic Latent disease: disease with a period of no symptoms when the causative agent is inactive Shingles

Vaccinations Can provide short term or long term immunity against certain diseases. Can stop diseases from spreading rapidly. Herd immunity: immunity in most of a population

Extent of Host Involvement Local infection: pathogens are limited to a small area of the body; where they enter Abscesses Systemic infection: an infection throughout the body spread by lymph or blood Measles Focal infection: systemic infection that began as a local infection Strept throat  Scarlet Fever

Extent of Host Involvement Sepsis: toxic inflammatory condition arising from the spread of microbes, especially bacteria or their toxins, from a focus of infection Bacteremia: bacteria in the blood not multiplying Septicemia: growth of bacteria in the blood Toxemia: toxins in the blood Viremia: viruses in the blood

Extent of Host Involvement Primary infection: acute infection that causes the initial illness Chicken pox- pustules Secondary infection: opportunistic infection after a primary (predisposing) infection Staphylococcus aureus- infection of pustules due to child scratching Subclinical disease: no noticeable signs or symptoms (inapparent infection) Poliovirus, Hepatitis A

Predisposing Factors Make the body more susceptible to disease Short urethra in females Inherited traits, such as the sickle cell gene Climate and weather Fatigue Age Lifestyle Chemotherapy

Development of Disease Incubation period- period from initial infection until signs/symptoms are present; varies Prodromal period- Mild symptoms Period of Illness- Most severe signs/symptoms Period of Decline- Signs/symptoms start to go away and get better Period of Convalescence- Recovery

Incubation period (no signs or symptoms) Figure 14.5 The stages of a disease. Period of illness Period of decline Incubation period (no signs or symptoms) Prodromal period (mild signs or symptoms) Number of microbes Period of convalescence Most severe signs and symptoms Signs and symptoms Time

Reservoirs of Infection Continual sources of infection Humans: AIDS, gonorrhea Carriers may have inapparent infections or latent diseases Animals: rabies, Lyme disease Some zoonoses may be transmitted to humans Nonliving: botulism, tetanus Soil Water

Transmission of Disease Contact Direct: requires close association between infected and susceptible host Indirect: spread by fomites Droplet: transmission via airborne droplets Small droplets travel farther (Airborne) Large droplets travel not as far (Droplet)

Vehicle Transmission Transmission by an inanimate reservoir (food, water, air) Salmonella, Cholera, and Fungal infections

Vectors Arthropods, especially fleas, ticks, and mosquitoes Transmit disease by two general methods: Mechanical transmission: arthropod carries pathogen on feet Houseflies, roaches Biological transmission: pathogen reproduces in vector Trypansoma sp.

Figure 14.8 Mechanical transmission. Vectors

Nosocomial Infections Are acquired as a result of a hospital stay or other healthcare settings Affect 5–15% of all hospital patients Increased in the last 20 years United States Statistics: 2 million/year 20,000 deaths/year 8th cause of death

Figure 14.6b Contact transmission. Preventing direct contact transmission through the use of gloves, masks, and face shields

Microorganisms in hospital environment Figure 14.9 Nosocomial infections. Microorganisms in hospital environment Compromised host Nosocomial infection Chain of transmission

Common Causes of Nosocomial Infections Percentage of Total Infections Percentage Resistant to Antibiotics Coagulase-negative staphylococci 15% 89% S. aureus 80% Enterococcus 10% 4–71% Gram-negative rods 15–25% 3–32% C. difficile 13% Not reported

Compromised Host Resistance to infection is impaired due to Disease- suppresses immune system Surgery- incisions, anesthesia Invasive procedures- putting things in the body that don’t belong there Burns- missing skin Drugs- can suppress immune system

Chain of Transmission Equipment being reused. Contract from healthcare worker (passive carrier) Patients grouped together in one area for specific treatments Invasive procedures

Control of Nosocomial Infections Aseptic techniques Proper handling of contaminated materials Handwashing Staff education Isolation Prescribing antibiotics only when necessary Infection control committees

Emerging Infectious Diseases Diseases that are new, increasing in incidence, or showing a potential to increase in the near future

Emerging Infectious Diseases Contributing factors Genetic recombination E. coli O157, avian influenza (H5N1) Evolution of new strains V. cholerae O139 Inappropriate use of antibiotics and pesticides Antibiotic-resistant strains Changes in weather patterns Malaria

Emerging Infectious Diseases Modern transportation West Nile virus Ecological disaster, war, and expanding human settlement Animal control measures Lyme disease Public health failure Diphtheria

Epidemiology The study of where and when diseases occur Centers for Disease Control and Prevention (CDC) Collects and analyzes epidemiological information in the United States Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov Paper/report will come from this publication. Information for the paper is on Blackboard under Course Content in the MMWR PAPER folder.

Epidemiology Descriptive: collection and analysis of data Snow Analytical: comparison of a diseased group and a healthy group Nightingale Experimental: controlled experiments Semmelweis

Epidemiology Case reporting: health care workers report specified disease to local, state, and national offices Nationally notifiable diseases: physicians are required to report occurrence

The CDC Morbidity: incidence of a specific notifiable disease Mortality: deaths from notifiable diseases Morbidity rate: number of people affected in relation to the total population in a given time period Mortality rate: number of deaths from a disease in relation to the population in a given time

Number of reported cases Figure 14.10 a & b Epidemiological graphs. 40,000 35,000 30,000 25,000 Number of reported cases 20,000 15,000 10,000 5,000 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 (a) Lyme disease cases, 1999–2010 600 500 400 300 Reported cases per 100,000 people 200 100 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month (b) Lyme disease by month, 2009

Reported tuberculosis cases, 1948–2010 Figure 14.10c Epidemiological graphs. 120 100 80 60 40 20 Reported cases per 100,000 people 1948 1958 1968 1978 1988 1998 2008 Year Reported tuberculosis cases, 1948–2010