1. Infection and Disease

2. The Host-Microbe Relationship
Human body maintains a symbiosis with microbes
Infection refers to:
relationship between the host and microbe
competition for supremacy between them
If the host loses the competition, disease occurs

3. Contact, Colonization, Infection, Disease
condition where pathogenic microbes penetrate host defenses
enter tissues and multiply
Disease
any deviation from health, disruption of a tissue or organ
infectious disease
Caused by microbes or their products

4. **Not all contacts lead to infections…….
**Not all infections lead to disease!!!!!

5. Resident Flora Microbiota, transient, resident, indigenous
Microbes that engage in mutual or commensal associations
most areas of the body in contact with the outside environment
internal organs & tissues & fluids are microbe-free
bacterial flora benefit host by preventing overgrowth of harmful microbes

6. Initial Colonization of the Newborn
Uterus and contents normally sterile
remain so until just before birth
Breaking of fetal membrane exposes the infant
all subsequent handling and feeding continue to introduce normal flora

7. Pathogens…. True pathogens Opportunistic pathogens
capable of causing disease in healthy persons
normal immune defenses
influenza virus, plague bacillus, malarial protozoan
Opportunistic pathogens
cause disease when hosts defenses are compromised
Pseudomonas sp & Candida albicans

8. Pathogenicity Ability of a microorganism to cause disease
Severity of disease depends on the virulence of the pathogen
Degree of pathogenicity
characteristic or structure that contributes to the ability of a microbe to cause disease
virulence factor
Adhesion factors
Biofilms
Extracellular enzymes
Toxins
Antiphagocytic factors

9. Pathogens….. In order to become established: Portal of entry Attaching
Surviving host defenses

10. 1. Portals of entry
characteristic route a microbe follows to enter the tissues of the body
skin
nicks, abrasions, punctures, incisions
gastrointestinal tract
food, drink, and other ingested materials
Mucous membranes
urogenital tract
Sexual
transplacental

11. Infectious Dose (ID)
minimum number of microbes required for infection to proceed
microbes with small IDs have greater virulence
1 rickettsial cell in Q fever
10 bacteria in TB, giardiasis
109 bacteria in cholera

12. 2. Mechanisms of Adhesion
fimbrae
flagella
adhesive slimes or capsules
cilia
scolex
hooks
barbs

13. 3. Surviving Host Defenses
Initial response of host defenses comes from phagocytes
Ability to survive intracellular phagocytosis
Antiphagocytic factors

14. Antiphagocytic factors
Factors prevent phagocytosis by the host’s phagocytic cells
Bacterial capsule
Composed of chemicals not recognized as foreign
Slippery; difficult for phagocytes to engulf bacteria
Antiphagocytic chemicals
Prevent fusion of lysosome and phagocytic vesicles
Leukocidins directly destroy phagocytic white blood cells

15. Enzymatic Destruction
Extracellular enzymes (exoenzymes)
Secreted by the pathogen
Dissolve structural chemicals in the body
Help pathogen maintain infection, invade, and avoid body defenses

16. Invasiveness Coagulase Streptokinase Hyaluronidase Leukocidins
form a blood clot that protects them from phagocytosis
Streptokinase
dissolves fibrin clots and allows dissemination of the bacteria
Hyaluronidase
enhances pathogen penetration through tissues
Leukocidins
disintegrate neutrophils and macrophages
Hemolysiins
dissolve red blood cells
Virulence can be enhanced in biofilms
immune cells cannot reach bacterial cells

17. Toxins
toxigenicity
capacity to produce toxins at the site of multiplication
endotoxins
lipid A of LPS of gram-negative bacteria
exotoxins
proteins secreted by gram-positive and gram-negative bacteria

19. Toxins Toxinoses Toxemias Intoxication Enterotoxins Antitoxins Toxoids
Disease caused by toxin
Toxemias
Spread by blood
Intoxication
Ingested
Enterotoxins
act on the gastrointestinal tract
Antitoxins
produced by the host body and neutralize toxins
Toxoids
toxins whose toxicity has been destroyed but still elicit an immune response

20. Portals of Exit Respiratory, saliva Skin Fecal exit Urogenital tract
Removal of blood

21. Establishment of Infection and Disease
incubation period
time between entry of the microbe and symptom appearance
prodromal phase I
time of mild signs or symptoms
acme period (climax)
signs and symptoms are most intense
period of decline
As sign and symptoms subside
period of convalescence
body systems return to normal

22. Patterns of Infection localized infection focal infection
remains confined to a specific tissue
focal infection
when infectious agent breaks loose from a local infection
carried to other tissues
systemic infection
infection spreads to several sites and tissue fluids
usually in the bloodstream

23. Patterns of Infection Mixed infection Primary infection
several microbes grow simultaneously at the infection site
Primary infection
initial infection
Secondary infection
another infection by a different microbe

24. Warning Signals of Disease
objective evidence of disease as noted by an observer
Symptom
subjective evidence of disease as sensed by the patient
Syndrome
Disease is defined by complex of signs and symptoms

25. Signs and Symptoms of Inflammation
Earliest symptoms of disease as a result of the activation of the body defenses
fever, pain, soreness, swelling
Signs of inflammation:
edema
accumulation of fluid
granulomas and abscesses
walled-off collections of inflammatory cells and microbes
Lesion
General term for site of infections or disease

26. Signs of Infection in the Blood
Changes in the number of circulating white blood cells
leukocytosis
increase in white blood cells
leukopenia
decrease in white blood cells

27. Signs of Infection in the Blood
septicemia
microorganisms multiplying in the blood and present in large numbers
bacteremia
small numbers of bacteria present in blood
not necessarily multiplying
viremia
small number of viruses present

28. Infections That Go Unnoticed
Asymptomatic
subclinical infections
although infected, the host doesn’t show any signs of disease
Inapparent infection
person doesn’t seek medical attention

29. Persistence of Microbes and Pathologic Conditions
Latency
microbe can periodically become active
produce a recurrent disease
person may or may not shed it during the latent stage
Sequelae
long-term or permanent damage to tissues or organs
Acute diseases
develop rapidly
cause severe symptoms
fade quickly
Chronic diseases
linger for long periods of time
slower to develop and recede

30. Reservoirs: Where Pathogens Persist
primary habitat of pathogen in the natural world
human or animal carrier, soil, water, plants
Source
individual or object from which an infection is actually acquired

31. Animals as Reservoirs and Sources
vector
live animal that transmits an infectious agent from one host to another
Arthropods
fleas, mosquitoes, flies, and ticks
larger animals
mammals, birds, lower vertebrates

32. Animals as Reservoirs and Sources
zoonosis
infection indigenous to animals but naturally transmissible to humans
humans do not transmit the disease to others

34. Acquisition and Transmission of Infectious Agents
Communicable disease
an infected host can transmit the infectious agent to another host
Highly communicable disease is contagious
Non-communicable infectious disease
does not arise through transmission from host to host
occurs primarily when a compromised person is invaded by his or her own normal microflora
contact with organism in natural, non-living reservoir

35. Patterns of Transmission
Direct contact
physical contact, droplet nuclei, aerosols
Indirect contact
passes from infected host to intermediate conveyor and then to another host
vehicle
food, water, biological products, fomites

36. Nosocomial Infections
Health care-associated infections (HAIs)
occur as a result of receiving treatment for another condition
Nosocomial infections are HAIs associated with hospitals
They occur as a result of chains of transmission

37. Nosocomial Infections
From surgical procedures, equipment, personnel, and exposure to drug-resistant microorganisms
More than 1/3rd of nosocomial infections could be prevented
2 to 4 million cases/year in U.S.
approximately 90,000 deaths
Most common organisms involved
Gram-negative intestinal flora
E. coli, Pseudomonas, Staphylococcus

38. Epidemiology
study of the frequency and distribution of disease & health-related factors in human populations
Surveillance
collecting, analyzing, & reporting data on rates of occurrence, mortality, morbidity and transmission of infections
Reportable, notifiable diseases must be reported to authorities

39. Epidemiology
Centers for Disease Control and Prevention (CDC) in Atlanta, GA
principal government agency responsible for keeping track of infectious diseases nationwide

40. Epidemiology Prevalence
total number of existing cases with respect to the entire population usually represented by a percentage of the population
Prevalence= Total # of cases in pop X Total # of persons in pop

41. Epidemiology Incidence
measures the number of new cases over a certain time period, as compared with the general healthy population
Incidence = # of new cases = ratio # of healthy persons

42. The incidence and estimated prevalence of AIDS

43. Epidemiology Mortality rate Morbidity rate
total number of deaths in a population due to a certain disease
Morbidity rate
number of people afflicted with a certain disease

44. Epidemiology
Endemic
disease that exhibits a relatively steady frequency over a long period of time in a particular geographic locale
Sporadic
when occasional cases are reported at irregular intervals
Epidemic
when prevalence of a disease is increasing beyond what is expected
Pandemic
epidemic across continents