Chapter 19. Infection and Disease
o Employ epidemiologists; disease investigators.
o Try to prevent disease; halt the spread of epidemics.
o Prevention strategies; clean filters, isolate people, etc…
• In the 1970s, it was thought that infectious disease was going to be
o However, this statement was made before the prominence of
antibiotics resistant bacteria and new emerging diseases without
treatment (HIV, Ebola, Zika).
Microbes are Everywhere
• Microbiota: the population of microorganisms the reside normally in
the body without causing disease.
o Colonization bacteria; competes for the same nutrients.
o Secrete antimicrobial compounds.
o Microbiota are received from birth and remain until death.
o Indigenous: have permanent relationship with body.
▪ E. coli, C. albicans.
o Transient microbiota: temporary, found only for limited periods
▪ Mutualism: beneficial to both host and microbe.
▪ Commensalism: beneficial only to the microbe and the
host is unaffected.
▪ Parasitism: pathogen causes damage to host, potentially
causing disease. • Chlamydiae.
• Surgeries, wounds, and other injuries can introduce pathogens to the
body, possibly replacing the body’s natural microbiota.
o Antibiotics and other drugs can have the same effect.
• Protection of microbiota:
o Probiotics; avirulent, nonpathogenic microbes similar to gut
o Competes with pathogen and restore microbiota.
The Host-Microbe Relationship
• Inflammation is the first sign that the immune system is beginning to
• Anything that alters the normal good healthy behavior of the body is a
disease causing agent.
o If you have a pathogenic bacteria but are not affected by the
disease negatively, you are not really diseased.
• Cerebrospinal fluid
• Joint fluid
o Ex. knee, ankle, hip, wrist, ankle.
• Internal organs
o Ex. kidneys, liver, muscles, lymph node, brain, heart, spleen,
Any Microorganism Can Become Virulent
• Microorganisms can change genetically and become virulent.
• Can obtain virulent genes located on plasmid from another microbe
Progression and Outcomes of Infection and Disease
• Primary: occur in healthy bodies.
2 • Secondary: occur in body weakened by a primary infection.
o Example: 1918-1919 influenza pandemic.
• Local: focused area of infection upon a single area of the body.
• Systemic: focus of infection to organs and systems via blood.
o Example: Staphylococci.
• Bacteremia: transient appearance of bacteria in blood.
• Septicemia: growth and spread of bacteria in blood.
o Potentially life threatening; bacterial division occurs very fast.
• Viremia: detection of viruses in the blood.
• Toxemia: presence of toxins in the blood.
Establishment of Infection and Disease
• Diseases progress through a series of stages.
o Signs (detected by observer), symptoms (observed by patient),
and syndromes (signs and symptoms together; characterize
• Course of Disease:
o Acute: develop quickly and fades away quickly.
o Chronic disease: lingers; slow to develop and slow to recede.
The Body Is Composed of Portals
• Pathogens enter and leave the host through orifices on the body.
• Pathogens can spread thro