STIs Flashcards
(95 cards)
What are common features of STIs?
• Shared mode of transmission (sexual)
- =shared mode of prevention
- More than one infectious agent often present (hunt in packs)
- Enhances HIV transmission/acquisition
- Can be asymptomatic and transmissible
- Often persistent infections with significant consequences
- Stigma can prevent treatment, possible eradication
What are the features and examples of bacterial STIs?
- Chlamydia tranchomatis
- Neisseria gonorrhoea
- Treponema pallidum
- Very infectious, easy spread
- Humans only
- Effective antibiotic treatment
- Prevent with condoms
What are part of the Chlamydia genus? Where do they cause infection?
Chlamydia tranchomatis
- Serovars A,B,C – trachoma
- Serovars D-K – conjunctivitis, urogenital tract infections, pneumonitis
- Serovars L1-L3 – lymphogranuloma venereum
Chlamydophila pneumonia – atypical pneumonia
Chlamydophila psittaci – acute respiratory disease
What are features of Chlamydia trachomatis serovars D-K?
- Most common bacterial STI (developed world)
- Many asymptomatic
- Can infect eye • Discharge
- Can ascend upper genital tract cause infection and damage
- Can be passed to newborns
- Persistent infections common
What are features of Chlamydiae bacteria?
- Gram negative
- Small
- Wont detect peptidoglycan in cell wall (no gram stain)
- Observe lymphocyte response
- LPS truncated, not very endo-toxic
- Obligate, intracellular (need host mitochondria for energy)
- Therefore need cell culture
- Slow replication with EB and RB stage
- Damage due to host immune response
What’s involved in the replication cycle of Chlymadiea?
• Slow and 2 development stages (elementary body/EB and reticulate body/RB)
What happens during chlamydia entry, multiplication and spread?
- Elementary body (binds columnar epithelial cells by adhesins, RME
- Endosome with EB doesn’t fuse with lysosome (no destruction). Endosomes fuse to form inclusions
- EB transformed to metabolically active reticulate body. RB replicates in inclusions
- RB converted to EB and EB released
What are EB and RB and how do they differ?
- elementary body = infectious, extracellular particle (no replication, no antimicrobial susceptibility)
- reticulate body = intracellular, replicative, don’t survive outside cells, targeted by microbials but they need to penetrate cell and tissue, If IFNγ present (from T cells, macrophage), prolong RB phase, low grade chronic inflammation and tissue damage
How does chlamydia cause damage?
- Infected epithelial cells, make chemokines so influx of neutrophils, monocytes, DCs, NK cells
- T and B cells activated and accumulate to form follicles
- Continuing activation = chronic inflammation
- Persistent inflammation due to hsp60 from chlamydial
- Recurrent infections
How can chlamydia be diagnosed and treated?
- Swabs, first pass urine specimens
- PCR
- EIA less common
- Tetracycline or macrolide antibiotics
- Good penetration
- Given over prolonged time
• azithromycin
What is the preferred treatment for chlamydia?
• Single dose long acting macrolide/azithromycin ideal
What are the features of Neisseria gonorrhoea?
- Gonorrhoea
- Gram negative diplococcus
- Intracellular mostly
- Likes to grow in Co2 (but not anaerobe)
- Similar clinical presentation to chlamydia
- Symptomatic = urethritis
- Can ascend in females, cause pelvic inflammatory disease (PID)
- Predominately for gays
How does gonorrhoea enter, spread and multiply in us?
- Target columnar epithelial cells like chlamydia
- Attach with adhesins (pili, OM proteins, LPS with no O antigen/lipo-oligosaccharide)
- Cell surface replication • Spread in mucus secretions (pili twitching motility)
- And invade and go to sub-epithelial tissue, Inflammation/dissemination
Why is complement and neutrophil activation poor by gonorrhoea?
• Poor complement/neutrophil activation because altered LPS and lack some OM proteins
How does gonorrhoea cause damage?
- No exotoxins
- Inflammatory response (PRR, LPS, peptidoglycan)
- Pus, pain
- TNF causes loss of ciliated epithelial cells
- Invasive strains avoid complement cascade/neutrophils
- Prolonged infection due to antigenic variation in pili, surface proteins
- Can acquire other genetic material (antibiotic resistance)
How is gonorrhoea diagnosed?
- Culture and gram stain
- PCR
- Microscopy (gram neg diplococcic and polymorphonuclear neutrophils)
What kind of culture is needed for gonorrhoea and why?
- Often normal flora present, need selective enriched medium
- Gonococcus Medium (GN)
- Lysed HBA biplate
- One side antibiotics, selective for Gonococcus
- Culture essential for working out antibiotic susceptibility
How can gonorrhoea be treated?
- Check guidelines
- Beta-lactamase resistant cephalosporin
- Also use azithromycin as 40% have chlamydia too
What causes syphilis? What are the features of this bacterium?
- Treponema pallidum
- Spirochaete family (some normal microflora)
- Slender, spiral rod, need special to visualise
- Motile with contractile flagella
- Labile, easy to inactivate
- Non culturable
- Possible spread from placenta to foetus
- Asymptomatic or symptomatic
What are the stages of syphilis infection and what is involved in each stage?
Infection
- 3 weeks
- Multiply and disseminate into blood/tissue
Primary syphilis
- Local ulcer (chancre)
- Or asymptomatic (2-24 weeks)
- 2-6 weeks – control by immune system, resolution or continuation
Secondary syphilis
- Genital lesions, rashes, warts
- Bacteria localise in tissue to cause symptoms
- Asymptomatic (3-30 years)
- 2-6 weeks – control by immune system, resolution or continuation
Tertiary syphilis
- Targets other important organs
- Multiplication and hypersensitivity response
How long can someone be asymptomatic at each stage of syphilis infection?
- Primary 2-24 weeks
- Secondary 3-30 years
How is syphilis diagnosed?
Dark ground microscopy and PCR rarer
Serology
- Detect antibodies to treponemal antigens
- Rapid plasma reagin test (RPR)
What is the basis of the rapid plasma reagin test?
- Measure abs made against components of damaged cells – cardiolipin
- Very sensitive (not many false negatives)
- Not very specific (some false positives)
- Cheap
- Screening test
- Need confirmation with specific tests, EIA
How is syphilis treated?
- Sensitive to penicillin
- No resistance
- Need to prevent progression
- Need to prevent congenital syphilis (screen pregnant mums)