Jackson: Host-Parasite Relationships Flashcards
Portals of Entry:
• Skin:
Arthropod vectors:
Strep and staph bind to:
Primary barrier to infection but some pathogens can traverse it
Arthropod vectors inject pathogens into humans
Strep and staph bind to fibronectin in wounds and indwelling devices
Portals of Entry:
• Lungs:
How do pathogens overcome ciliary action? (2)
o Adapt Strong Adhesins:
o Paralyze Ciliary Action:
Adapt Strong Adhesins:
Rhinovirus:
Mycoplasma:
Adapt Strong Adhesins:
• Rhinovirus uses capsid protein for attachment to ICAM-1-type molecule
• Mycoplasma pneumonia attaches to neuramic acid on host respiratory epithelium
Paralyze Ciliary Action:
Bordetella pertussis:
Influzena virus infection:
Paralyze Ciliary Action:
• Bordetella pertussis produces tracheal cytotoxin
• Influzena virus infection causes ciliated cell dysfunction
Gastrointestinal Tract:
Intestinal pathogens express:
Receptor specificity dictates:
Where are adhesins typically located? Why?
- Some microbes enter through what type of cells of Peyer’s patches?
Gastrointestinal Tract:
- Intestinal pathogens express receptor-specific adhesins
o Receptor specificity dictates colonization site and pathogenesis
o Adhesins typically located on the tip of bacterial pili to overcome cell-cell repulsion
- Some microbes enter through antigen sampling cells of Peyer’s patches
What are the best defense for the GI tract?
Disruption leads to:
What causes enterocolitis?
Resident microflora are the best defense for GI tract:
o Disruption can lead to opportunistic infections
o Antibiotic-associated enterocolitis is caused by overgrowth of resident opportunist
Urogenital Tract:
Vaginal pathogens:
Urethral Pathogens:
Primary defense (3):
Why are females more susceptible to UTIs?
Vaginal Pathogens: must colonize mucosa or take advantage of localized injuries
Urethral Pathogens: primary defense is flushing action of urine; mucus lining of the bladder and sIgA also provide defense against UTIs
o Female more susceptible to UTIs because of shorter urethra
Urogenital Tract:
What do UTI pathogens (E.coli) have that permits ascending infections?
UTI pathogens (E.coli) have adhesins that permit ascending infections
- Adhesins specialized for urinary epithelium
- Inflammatory response to UTI causes pathology
Different Mechanisms of Transmission (5):
- Respiratory
- Fecal-oral
- Sexual contact
- Vector-borne (malaria), person-person, or animal-person (rabies)
- Vertebrate reservoir (plague)
Routes of Infection:
Some pathogens transiently infect at a primary layer and rapidly shed (2):
Some pathogens invade deeper tissues and may be shed from secondary site (1):
Routes of Infection:
Some pathogens transiently infect at a primary layer and rapidly shed (influenza and Shigella)
Some pathogens invade deeper tissues and may be shed from secondary site (Varicella)
Vertical vs. Horizontal Transmission:
Vertical: from parent to offspring, via placenta, sperm, ovum, blood or milk
Horizontal: from person to person
Infectious Dose (ID50): Variance:
ID can vary: can range from very small (ie. only 10 cells) to very large (ie. 10,000,000 cells)
10: Shigella
10,000,000: Vibrio cholerae
Route of Infection Important:
What is the most effective means of person-to-person transmission?
Aerosol is the most effective means of person-to-person transmission
o Successful infections depend on receptors and localized defenses
Rhinovirus Route of Entry: Nasal vs. pharynx
A single rhinovirus particle in the nasal cavity causes successful infection
200 rhinovirus particles are required for infection if inoculation occurs in the pharynx
Stability of Organism in Environment: another factor involved in transmission.
Spore producing vs respiratory and STDs
Respiratory and sexually transmitted pathogens are unstable: need person-to-person contact
Spore producing organisms: spores can persist in the environment for years
Microbe Replication Rates:
E. coli vs Mycobacteria
- Can take minutes (E.coli) or days (Mycobacteria spp.) to double
Susceptibility to Infection is Influenced by Genetic Determinants in the Host:
Host Specificity (measles, Shigella vs rabies):
Some pathogens only infect humans or closely related primates (measles, Shigella)
Others are capable of infecting a wide range of hosts (rabies)
Intraspecies Genetic Determinants Dictate Susceptibility:
Sickle cell: heterozygous vs aa:
Effect to Plasmodium falciparum parasite:
Individuals heterozygous for sickle cell trait are less susceptible to malaria
Sickle cell trait due to aa substitution in Hb (HbS)
Result is Plasmodium falciparum parasite (causes malaria) is unable to utilize the altered Hb