Lec 33 - STIs

Question 1

Why is there more opportunity to control STIs rather than other diseases eg respiratory diseases

Answer 1

• STIs linked to social and sexual behaviour rather than just biology

Question 2

Why are we experiencing a rise in STIs in recent years?

Answer 2

• introduction of the pill has removed use of barrier methods for protection against STIs eg condoms
• attitudes towards sex has changed - more sex and increased use of dating apps
• rise of resistant strains of STIs

Question 3

Give 5 examples of STIs and state their cause

Answer 3

1. HIV - AIDS
2. Hep A/B/C - Hepatits (both viral)
3. Chlamydia trachomatis - Chlamydia
4. Trepomona pallidum - Syphillis
5. Neiserria gonorrhoae - Gonorrhoae

Question 4

What type of pathogen are bacterial STIs? Describe what this means

Answer 4

• STRICT
• highly adapted to the host
• person;person spread w/ no animal resevoir

Question 5

Give the name of bacteria that causes Gonorrhoea and state its structure when observed in discharge

Answer 5

• Neisseria gonorrhoea*
• Gram -ve coccus, high proportions of diploccoci

Question 6

How is Neisseria gonorrhoea transmitted and can it be grown in pure culture?

Answer 6

• transmitted through intimate mucosal contact eg vagina and urethral mucosa (of penis)
• yes it can be grown in pure culture although does not survive well outside of the host

Question 7

What are the symptoms of gonorrhoea?

Answer 7

• males - thick dischagre, pain on urination
• females - vaginal discharge

Question 8

What are the problems that can arise because of the fact that 50% of females are asymptomatic?

Answer 8

• damage to the fallopian tubes leading to infertility
• during pregnancy, N. gonorrhoea can colonise the eyes leading to blindness
• because of the high proportion of asymptomatics need to contact sexual partners of symptomatics to prevent spread

Question 9

Give 4 examples of the VFs found in N. gonorrhoea

Answer 9

1. capsule - resist phagocytosis
2. pili and Protein II - adhering to the host cells
3. IgA protease - breakdown secretory IgA
4. Tbp/Lbp - acquire Fe from host cell

Question 10

How does N. gonorrhoea evade the immune system?

Answer 10

MOLECULAR MIMICRY

• sialylation of LPS residues prevents immune response because makes it look like host cells

ANTIGENIC VARIATION

• phase variation and differential antigenic expression means that the immune system cannot provide an effective response

Question 11

Give an example of antigenic variation in N. gonorrhoea

Answer 11

Differing the pilin proteins expressed on the surface because they are immunogenic. PilE normally expressed but RecA mediated recombination between pilE and pilS (silent loci) can create variants

Question 12

What antibiotics can be used to treat gonorrhoea and what is a mjor problem associated with the disease currently?

Answer 12

• both penicillin and fluoroquinolones have been used in the past however HIGH levels of resistance now
• cephalosporins used - however increasing resistance
• major problem = multi drug resistant strains now exist. looking v real that we will have untreatable gonorrhoea

Question 13

What bacteria causes Syphillis?

Answer 13

Treponema pallidum

Question 14

What phylum does Trepomponas pallidum belong and what is its main feature?

Answer 14

• Spirochaetes
• has a flagellum within the periplasm - helps to rotate the whole cell so can swim through mucus etc

Question 15

How is syphillis passed on ?

Answer 15

• intimate sexual contact
• require minor tissue adrasions that occur during sex

Question 16

Draw a diagram that illustrates the lifecycle of Trepomponas pallidum and at each stage list the symptoms

Answer 16

Question 17

List the 5 main ways that T. pallidum can survive in the host long-term

Answer 17

1. lack of surface proteins / antigens - 1% that of E. coli and only integral protein may play a major role in attachment to host?
2. few organisms required to establish infection - due to the SLOW growth of T. pallidum only a few organisms at distant sites required theefore critical antigenic mass is not reahed to stimulate immune system
3. lack of endotoxin/LPS therefore doesnt stimulate IR. also when attached to cells do not kill them sugesting no cytolytic enzymes released
4. invade immune privilidged cells eg CNS, eye, placenta
5. low requirement for Fe/can obtain from cells - lack of Fe containing enzymes (use other metal ion cofactors) , no ETC (which uses Fe based enzymes)

Question 18

What feature of T. pallidum means that is causes CHRONIC infection

Answer 18

slow growing

Question 19

Describe the treatment of Trepomponas pallidum

Answer 19

due to slow growing nature, high doses of penicillin need to be given for a few weeks

daily injections of IV penicillin

Question 20

What disease is also correlated to syphillus infection?

Answer 20

co infection with HIV

Question 21

Describe Chlamydia and state the bacteria that causes it

Answer 21

• Chlamydia trachomatis
• wall-less obligate, intracellular parasite

Question 22

Draw a diagram to illustrate chlamydia life cycle and describe the 2 forms that exist

Answer 22

EB - ELEMENTARY BODY - required for survival outside of cellsand invovled in invasion

RB - RETICULATE BODY - intracellular growth

Question 23

Do all serovars of Chlamydia result in STIs?

Answer 23

no, only strains D/K result in STIs - urethritis (men) & cervicitis (women)

Question 24

Describe the symptoms of chlamydia is men and women

Answer 24

men - thin watery dischagre, pain on urination

women - cervisitis, urethra infection, infertility & ectopic pregnancy

Question 25

how is chlamydia treated?

Answer 25

because no peptidoglycan, B lactams do not work therefore need tetraclycine/doxycycline - side effects