Ch.14 part 1

• The notes have been updated with all new information that you provided.

Pathology, Infection, and Disease

• Pathology is the study of disease
• Etiology refers to the cause of a disease
• Pathogenesis describes the development of disease
• Infection is the invasion or colonization of the body by pathogens
• Disease is an abnormal state where the body isn't performing normal functions

Normal Microbiota

• Transient microbiota may be present temporarily for days, weeks, or months
• Normal microbiota permanently colonize the host without causing disease under normal conditions
• The Human Microbiome Project analyzes relationships between microbial communities on our bodies and human health
• The distribution and composition of normal microbiota are determined by nutrients, physical/chemical factors, host defenses, and mechanical factors
• Microbial antagonism (competitive exclusion) involves competition between microbes
• Normal microbiota protect the host by competing for nutrients, producing harmful substances, and affecting pH/oxygen levels
• Symbiosis is the relationship between normal microbiota and the host
  • Commensalism benefits one organism without affecting the other
  • Mutualism benefits both organisms
  • Parasitism benefits one organism at the expense of the other
• Some normal microbiota can be opportunistic pathogens

Table 14.1 Representative Normal Microbiota by Body Region

• Skin microbiota includes Propionibacterium, Staphylococcus, Corynebacterium, Micrococcus, Acinetobacter, Brevibacterium, Candida (fungus), and Malassezia (fungus)
  • Most microbes in contact with skin don't become residents due to antimicrobial secretions from sweat/oil glands
  • Keratin is a resistant barrier
  • Low pH inhibits many microbes
  • The skin has relatively low moisture content
• Eye microbiota includes Staphylococcus epidermidis, S. aureus, diphtheroids, Propionibacterium, Corynebacterium, streptococci, and Micrococcus
  • The conjunctiva contains the same microbiota as the skin
  • Tears/blinking eliminate some microbes or inhibit others from colonizing
• Nose and Throat microbiota includes Staphylococcus aureus, S. epidermidis, and aerobic diphtheroids in the nose; S. epidermidis, S. aureus, diphtheroids, Streptococcus pneumoniae, Haemophilus, and Neisseria in the throat
  • Some normal microbiota are potential pathogens, but their ability to cause disease is reduced by microbial antagonism
  • Nasal secretions kill/inhibit many microbes, while mucus and ciliary action removes them
• Mouth microbiota includes Streptococcus, Lactobacillus, Actinomyces, Bacteroides, Veillonella, Neisseria, Haemophilis, Fusobacterium, Treponema, Staphylococcus, Corynebacterium, and Candida (fungus)
  • Abundant moisture, warmth, and food make the mouth ideal for large, diverse microbial populations
  • Biting, chewing, tongue, and saliva flow dislodge microbes
  • Saliva contains antimicrobial substances
• Large Intestine microbiota includes Escherichia coli, Bacteroides, Fusobacterium, Lactobacillus, Enterococcus, Bifidobacterium, Enterobacter, Citrobacter, Proteus, Klebsiella, and Candida (fungus)
  • The large intestine contains the largest number of resident microbiota due to available moisture/nutrients
  • Mucus and periodic shedding prevent microbes from attaching to the lining
  • The mucosa produces antimicrobial chemicals
  • Diarrhea flushes out some normal microbiota
• Urinary and Reproductive Systems contains Staphylococcus, Micrococcus, Enterococcus, Lactobacillus, Bacteroides, aerobic diphtheroids, Pseudomonas, Klebsiella, and Proteus in urethra; lactobacilli, Streptococcus, Clostridium, Candida albicans (fungus), and Trichomonas vaginalis (protozoan) in vagina
  • The lower urethra has a resident population; the vagina has an acid-tolerant population
  • Mucus and periodic shedding of the lining prevent microbes from attaching
  • Urine flow mechanically removes microbes
  • The pH of urine and urea is antimicrobial
  • Cilia and mucus expel microbes from the cervix into the vagina
  • Acidity in the vagina inhibits/kills microbes

The Etiology of Infectious Diseases

• Koch's postulates are:
  • 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's 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
• Koch's postulates are used to prove the cause of an infectious disease

Exceptions to Koch's Postulates

• Some pathogens can cause several disease conditions
• Some pathogens cause disease only in humans
• Some microbes have never been cultured

Classifying Infectious Diseases

• Symptoms are changes in body function felt by a patient due to disease
• Signs are measurable or observable changes in the body due to disease
• A syndrome is a specific group of signs and symptoms that accompany a disease
• A communicable disease is spread from one host to another
• Contagious diseases are easily and rapidly spread
• A noncommunicable disease is not spread from one host to another

Occurrence of a Disease

• Incidence is the number of people who develop a disease during a specific time period
• Prevalence is the number of people who develop a disease at a specified time, regardless of when it first appeared (includes old and new cases)
• A sporadic disease occurs only occasionally
• An endemic disease is constantly present in a population
• An epidemic disease is acquired by many people in a given area in a short time
• A pandemic disease is a worldwide epidemic

Severity or Duration of a Disease

• Acute disease develops rapidly but lasts only a short time
• Chronic disease develops slowly
• Subacute disease is intermediate between acute and chronic
• Latent disease has an inactive causative agent for a time before activating and causing symptoms
• Herd immunity is immunity in most of a population

Extent of Host Involvement

• Local infection limits pathogens to a small area of the body
• Systemic infection involves an infection throughout the body
• Focal infection is a systemic infection that began as a local infection
• Sepsis is a toxic inflammatory condition from the spread of microbes or their toxins from a focus of infection
• Bacteremia is bacteria in the blood
• Septicemia (blood poisoning) is the growth of bacteria in the blood
• Toxemia involves toxins in the blood
• Viremia involves viruses in the blood
• Primary infection is an acute infection causing the initial illness
• Secondary infection is an opportunistic infection after a primary infection
• Subclinical disease has no noticeable signs/symptoms (inapparent infection)

Patterns of Disease

• Predisposing factors, like gender, inherited traits, climate/weather, fatigue, age, lifestyle, nutrition, and chemotherapy, can make the body more susceptible to disease
• Development of Disease:
  • Incubation period: time between initial infection and first signs/symptoms
  • Prodromal period: a short period after incubation with early, mild symptoms
  • Period of illness: disease is most severe
  • Period of decline: signs and symptoms subside
  • Period of convalescence: body returns to its pre-diseased state