STIs and Emerging Infectious Diseases Flashcards
What are the 3 major STIs we study? (hint - bacterial infections)
How are they spread?
Chlamydia
Gonorrhoea
Syphilis
Spread directly from person-to-person with no animal reservoir
What disease is caused by Neisseria gonorrhoeae?
Traits of bacteria (3 traits)
Contact of what tissue type is needed for transmission?
Gonorrhoea
Gram -ve coccus; Diplococci in samples of discharge
Non-motile
Poor survival outside the human host but can be grown in pure culture
Intimate mucosal contact needed for transmission
Gonorrhoea symptoms? (2 gender specific symptoms)
Male - Thick urethral discharge; Pain on urination
Female - Vaginal discharge
What occurs in up to 50% of Gonorrhoea infected females?
Without treatment what can this lead to?
May be asymptomatic or have mild symptoms
No treatment can lead to infertility, transmission to baby during birth etc.
What is the key virulence factor of Neisseria gonorrhoeae?
Why is it key? (hint - mucosal surfaces)
What happens to importance of certain virulence factors as infection goes on?
Surface proteins and structures involved in adhesion and invasion of epithelial cells lining urethra/vagina
Good adhesion essential for a mucosal pathogen to prevent being dislodged by urine
Certain virulence factors become more important than others depending on infection stage
What is molecular mimicry? (hint - sialylation)
LPS is modified by attaching sialic acid to it so that it “looks” like host tissue to the immune system; Immune response not provoked
What is antigenic variation? (hint - gonococci)
Many surface proteins are highly immunogenic
Gonococci can produce hypervariable sequence variants that make it difficult for the immune system to mount an effective response
What is the method of antigenic variation in Pilin (pilE) gene
Partial sequence homology between the silent pilS loci and expressed pilE gene
This allows RecA-mediated recombination to occur, giving rise to a novel PilE variant protein by gene-conversion
What are the threats of asymptomatic carriers and resistant strains of gonorrhoea?
Asymptomatic carriers are major reservoirs of infection in the human population
Major problem with multi-drug resistant gonorrhoea; Possibility it becomes untreatable
What disease is caused by Treponema pallidum?
What type of bacterium is this?
- What shape?
Characteristics of growth and infection? (3 characteristics)
Causes Syphilis
Treponema pallidum is a spirocahaete; Spiral shape
Fragile and slow growing bacterium
Infection requires intimate sexual contact
Infection is chronic
Why is Syphilis a confusing disease to diagnose?
Has many symptoms which can be varied and easily confused with other disease
What are the 3 early stages of syphilis the disease can fluctuate between
- Mild or severe symptoms?
Final stage of syphilis?
- Mild or severe symptoms?
- How long for this to occur?
Early stages include:
- Primary
- Secondary
- Latent
These have milder symptoms
Late stage is Tertiary stage
More severe symptoms
Occurs after many years (5-50 years)
How does T. pallidum survive in host long-term? (5 ways)
Lack of endo- exotoxins
Invasion of “immune-privileged” tissues
Ability to maintain infection with few organisms
Lack of surface antigens
Low iron requirements and ability to obtain sequestered iron
T. pallidum survival - Lack of endo- and exotoxins (hint - LPS)
T. pallidum lacks LPS (endotoxin in Gram -ve outer membrane
This mean attachment of T. pallidum doesn’t harm target cell
T. pallidum survival - Invasion of “immune-privileged” tissues (hint - surveillance)
T. pallidum penetrates a broad variety of tissues, including “immune-privileged” tissues where there is less surveillance from innate immunity
T. pallidum survival - Ability to maintain infection with few organisms (hint - failure to trigger)
T. pallidum exploits its slow growth to survive in tissues
By maintaining infection with few organisms in distanced anatomical sites , T. pallidum may prevent its clearance by failing to trigger the host’s immune response, which may require “critical antigenic mass”
T. pallidum survival - Lack of surface antigens (hint- rare) (hint 2 - host interactions)
T. pallidum only has rare integral proteins in outer membrane
- 1% of number in E. coli outer membrane
However these rare proteins are important in interactions with host
T. pallidum survival - Low iron requirements and ability to obtain sequestered (removed) iron (3 points)
T. pallidum may acquire iron from host proteins
May also overcome iron sequestration by using enzymes that need metals other than iron
Lacks electron transport chain (made from iron using enzymes), decreasing overall iron demand
Main treatment for T. pallidum in which little resistance has developed for?
Why are high drug levels required for several weeks?
Penicillin
Slow growing bacterium so high drug level needs to be maintained
What type of parasite is the Chlamydia bacterium?
- Wall?
What is the life cycle? (hint - 2 functionally distinct cell forms)
Obligate intracellular parasite; Wall-less
Elementary Body (EB) - Survives outside of host cells and initiates infection
Reticulate Body (RB) - Differentiate from the EB and is responsible for intracellular growth
Male and Female symptoms of Chlamydia?
- Which is more often asymptomatic?
Male:
- Thin, watery urethral discharge
- Pain on urination
- Can be asymptomatic
Women:
- Cervix infection
- Urethritis
- Infertility and ectopic pregnancy
- Very often asymptomatic
Why is screening of Chlamydia important?
What are some treatments of Chlamydia? (hint - Wall-less)
Screening is important due to often asymptomatic infection
Chlamydia are insensitive to β-lactam antibiotics; No peptidoglycan
Alternatives include tetra-/doxycycline, but these have side effects
What factors result in the constant change of prevalence and patterns of infectious diseases? (3 factors)
These factors can result in changes in identification of pathogens. What does this cause? (hint - “new”
Changes in:
- Pathogen
- Environment
- Host population
Change sin identification can cause an existing pathogen to be identified as “new”
What are factors responsible for Emergence and Re-emergence of pathogens (5 factors)
- Look at reasoning for each
Globalisation and environmental change
New ways of growing and handling food
Natural disasters and breakdowns in public health
Changes in pathogens
Recognition of “new” pathogens
