Sexually transmitted infections

Question 1

STIs - Very common

Answer 1

• preventable infertility caused

- 1/3 of these <25 yr olds

Question 2

STIs are inctreasing

Answer 2

• increasing density and mobility of populations
• changing human sexual behaviour
• absence of vaccines

Question 3

Top 10 STIs

Answer 3

• gonorrhoea

- chlamydia

Question 4

Gonorrhoea (Neisseria gonorrhoeae)

Answer 4

• non motile, gram -ve diplococcus
• fastidious growth requirements
• carried in genital tract,nasopharynx, anus
• sensitive to drying

Question 5

Gonorrhoea

Answer 5

• can be asymptomatic

- F has 50% chance, M has 20% chance of becoming infected after single encounter

Question 6

Gonorrhoea -Clinically

Answer 6

F= 80% asymptomatic and at risk of pelvic inflammatory disease 
Symptoms= initial urethritis or cervicitis, can spread to uterus (Endometritis)
M=  10% asymptomatic
Symptoms = Urethritis, purulent discharge and dysuria

Question 7

Pathogenesis (Gon.)

Answer 7

Entry and adhesion - bacteria attach to the columnar epithelium via pili (non piliated strains are non-infective)
Rapidly multiply - some localised, others become systemic

Question 8

Pathogenesis (Gon.)

Answer 8

• invades epithelial cells and multiplies within vacuoles protected from antibodies and phagocytes)
• IgA protease
• Resist serum killing by complement

Question 9

Antigenic Variation

Answer 9

• capacity to genetically change surface structures - key for avoidance detection
• pili and outer membrane proteins (OMPS) - for adhesion to mucosal epithelium have hypervariable regions and & undergo frequent alteration

Question 10

Possible complications:

Answer 10

• infertility
• septicaemia
• arthritis
• meningitis
• endocarditis
• death
• ophthalmia neonatorum (severe purulent eye infection in infants born to infected mothers)

Question 11

Vaccine/treatment:

Answer 11

• No vaccine available (whole cell killed - ineffective, pili alone not effective)
• challenge is in antibiotic resistance
• treatment with single high dose of antibiotics (rapidly becoming untreatable)

Question 12

Chlamydia -Chlamydia trachomatis

Answer 12

• very small bacteria (obligate intracellular parasites)
• unable to replicate on own (adapted to intracellular existence)
• small genome= 1x10(6)kb (1/4 that of ecoli)
• limited biosynthetic capabilities
• obtains some preformed molecules from host cells

Question 13

EBs

Answer 13

Elementary bodies-adapted for extracellular survival

Question 14

RBs

Answer 14

Reticulate bodies- adapted for intracellular multiplication

Question 15

Elementary bodies…

Answer 15

enter the cells by parasite-directed endocytosis

-fusion of the phagosome with the lysosomes (and destruction of the bacteria) is inhibited

Question 16

Clinical Features(Chlamydia)

Answer 16

• Some C. trachomatis are “genital” strains (serotypes D-K) but also cause eye infections and pneumonia
• L1, L2, L3 strains cause LGV (lyphogranuloma venereun) - organism spreads to local lymph nodes
• ASYMPTOMATIC and easily spread

Question 17

Clinical Feature: Men vs Women

Answer 17

Men: arthritis, urethral infection
Women: PID, infertility

Question 18

Damage (women) due to:

Answer 18

1. direct destruction of cells
2. host inflammatory response to persistent infection
3. repeated exposure gives more severe disease
4. toxin?

Question 19

Treatment

Answer 19

• no vaccine

- antibiotic treatment (Tetracyclines, erythromycin)

Question 20

WHO control strategy

Answer 20

• promotion of responsible sexual behaviour
• access to treatment
• access to condoms