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Medical Microbiology and Virology > 22 Sexually transmitted infections > Flashcards

22 Sexually transmitted infections Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Why are STIs cases increasing?

Estimated 500 000 new cases per year

A 
Asymptomatic transmission
Increasing density/ mobility of humans
Change in human sexual practice
Absence of vaccine
Difficult to treat - resistant organisms

STI cases can occur with multiple infections. For example someone with syphilis, is more likely to ahve an additional STI

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2
Q

Which bacteria commonly cause STIs?

A

Chlamydia trachomatis
Haemophilus ducreyi (mainly tropical) - chancroid
Neisseria gonorrhoea
Treponema pallidum

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3
Q

What are treatments for these bacterial STIs?

Chlamydia trachomatis

  • D-K serotypes cause urethritis
  • L serotype - lymphogranuloma venereum

Haemophilus ducreyi (mainly tropical) - chancroid

A

Chlamydia trachomatis -

  • azithromycin 1g single dose
  • doxycycline 7 days

Haemophilus ducreyi - azithromycin, ceftriaxone

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4
Q

What are treatments for these bacterial STIs?

Neisseria gonorrhoea

Treponema pallidum

A

Neisseria gonorrhoea - ceftriaxone. Quinolone resistance common

Treponema pallidum - penicillin

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5
Q

Which viruses commonly cause STIs?

A

Papillomaviruses 6, 11, 16, 18 (warts/ cervical cancer)

HSV 1/2

HIV

Hepatitis B - transmitted sexually

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6
Q

What are treatments for these viral STIs?

Papillomaviruses 6, 11, 16, 18

HSV 1/2

A

Papillomaviruses - podophyllin, cryotherapy

HSV 1/2 - aciclovir, famciclovir

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7
Q

What are treatments for these fungal STIs?

Candida albicans - thrush

A

clotrimazole. fluconazole

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8
Q

Only one protozoa cause STIs.

What is treatment for Trichomonas vaginalis?

Often asymptomatic, can cause cancer

A

Metronidazole 2g single dose or

Metronidazole 400mg BD for 7 days

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9
Q

What are ectoparasite causes of STIs?

A

Sarcoptes sacbiei

Phthirus pubis

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10
Q

What are treatments for these ectoparasites?

Sarcoptes sacbiei

Phthirus pubis

A

Permethrin cream for both

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11
Q

How do STIs evade host defences?

  • integrity of mucosal surface
  • resist phagocytosis
A
  • integrity of mucosal surface - have specific attachment mechanism e.g gonococcus/ chlamydia
  • resist phagocytosis - induce little inflammation, or have capsule e.g treponema pallidum, gonococcus
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12
Q

How do STIs evade host defences?

  • affect complement
  • evade antibodies, especially IgA
A
  • affect complement - C3d receptor on pathogen bins C3b/d and reduces phagocytosis e.g candida
  • evade antibodies, especially IgA - produce IgA protease e.g gonococcus
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13
Q

How do STIs evade host defences?

  • cell mediated immunity
A
  • antigenetic variation allows re-infection with different strain e.g gonococcus/ chlamydia
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14
Q

What disease is caused by these spirochaetes ?

Treponema pallidum pallidum
Treponema pallidum pertenue
Treponema carateum
Borrelia burgdorferi
Borrelia recurrentis

Leptospira interrogans

A 
Treponema pallidum pallidum - syphilis
Treponema pallidum pertenue - yaws
Treponema carateum - pinta
Borrelia burgdorferi - lyme disease 
Borrelia recurrentis - relapsing fever

Leptospira interrogans - leptospirosis. Although this is a spiral organism, it is a leptospiraceae as opposed to spireochaetaceae

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15
Q

Syphilis enters the body through minute abrasions on skin or mucus membranes, and requires close contact. Organism does not survive outside body, and is sensitive to drying, heat, disinfectants.

Horizontal spread via sex
Vertical spread via transplancental

What is average incubation time?

What is length of latent period of syphilis?

A

3 weeks

3-30 years

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16
Q

What are stages of syphilis infection?

A

Primary infection - primary chancre - painless ulcer which heals spontaneously after 2 months. Lymphadenopathy. Teponemas multiply at site of infection/ lymph node

Secondary syphilis - flu like illness, myalgia, headache, fever, mucocutaenous rash. Resolves spontaneously

Latent syphilis - 3-30 years. Treponemas dormant in liver or spleen.

Tertiary syphilis - reawakening and multiplication of treponemas. Neurosyphilis, tabes dorsalis (demyelination of spinal cord), cardiovascular syphilis, heart failure. Gummas in skin, bone, testis

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17
Q

How does newborn present with congenital syphilis?

A

Intrauterine death

Congenital abnormalities - various

Silent infection - facial/ tooth deformities may only be seen by 2 years of age

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18
Q

T pallidum cannot be grown in vitro.

How is it diagnosed?

A

Dark field microscopy of exudate immediately after collection

Serology

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19
Q

Non-specific treponemal tests are

VDRL - veneral disease research laboratory
RPR - rapid plasma reagin test

How do they work and why are they non-specific?

A

Antigens are non-treponemal in origin

They are from extracts of cardiolipin from beef heart tissue, which allows detection of anti-lipid IgG/IgM formed in patient in response to lipoidal material released from cells damaged by infection (in addition to lipids on surface of T. Pallidum)

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20
Q

Non-specific syphilis tests are positive 1-2 weeks after primary chancre appears. Useful for initial screening test

Decline in positivity in tertitary syphilis or after treatment - can be used as vague indicator of treatment response.

What can cause false positive non-specific test? VDRL/ RPR

A 
Acute febrile disease
Collagen vascular disease
Drug abuse
Pregnancy
Malaria
Yaws/ Pinta
Viral infection
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21
Q

Specific treponemal test use recombinant proteins/ treponemal antigens extracted from T. pallidum

What are examples of these?

Specific tests remain positive life-long. Therefore cannnot be used to assess treatment response

A

Enzyme immunoassay (ELISA) test. Checks for syphilis antibodies IgM/ IgG

FTA-ABS - fluorescnet treponemal antibody absorption. Non-pathogenic treponemes added to blood, to remove cross-reacting antibodies, before reacting with actual host T pallidum antigens

TP-PA - based on the agglutination of coloured particle carriers sensitized with T pallidum antigen

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22
Q

What can cause false positive specific treponemal tests?

A 
AI disease- SLE
DM
Drug misuses
Lyme disease
Pregnancy
Viral infections
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23
Q

Interpretation of spyhilis tests

Nontreponemal/Treponemal 
                \+	+	
                \+	–	
                –	+	
               –	–
A

Nontreponemal tests/ Treponemal tests

+ + Syphilis, yaws or pinta

+ – False positive – No syphilis

– + Primary or latent syphilis; previously treated or untreated syphilis; yaws or pinta

– – No syphilis; incubating syphilis

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24
Q

Babies born to infected mothers need to be tested. How to distinguish congenital infection, from passive transfer antibodies across planeta?

A

Test sypihlis IgM at birth, and 6 weeks age. Maternal antibodies will wane, and if still raised indicates cognenital syphilis

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25
Q

What is treatment for syphilis?

A

Penicillin - also treats unborn baby
Doxycycline - but can’t be used pregnancy

Screen for other STIs
Contact tracing

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26
Q

Gonorrhoea caused by neisseria gonorrhoea. Often asymptomatic, which facilitates its transmission.

How is it transmitted?

A

Rquires close contact, as very sensitive to drying.

Sexual

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27
Q

What unique characteristic help gonorrhoea evade host reponse?

A

Adhesive pili prevent being washed away. Can bind to epithelium of vagina, penis, rectum, oropharynx. Have constant/ variable regions (like immunoglobulins), so provides antigenic diversity

Capsule resists phagocytosis

IgA protease protects from host secretory antibodies

Invade non-ciliated epithelial cells, which allow bacteria to multiply in intracellular vacuoles. Vacuoles move down through cell and fuse with basement membrane, discharging content into connective tissues. Stimulates inflammatory process and damage

28
Q

What symptoms does gonorrhoea cause?

A

Often asymptomatic - 50% women. Men more likely to be symptomatic

Dysuria
Urethral discharge
Vaginal discharge

Without diagnosis/ treatment -
Pelvic inflammatory disease
Infertility
Opthalmia neonatorum 
Endocarditis
Necrotic skin lesions - septic emboli
Septic arthritis
29
Q

How is gonorrhoea diagnosed?

A

Microscopy of exudate

Culture - resistance testing

30
Q

What is treatment for gonorrhoea?

A

Ceftriaxone and azithromycin (this also treats chlamydia)

Resistance to penicillin/ fluorquinolones

31
Q

What are the three difference chlamydia species, and what infections do they cause?

A

C trachomatis - trachoma, STI. Human natural host

C psitacci - pneumonia. Birds natural host

C pneumoniae - acute respiratory disease. Human natural host

32
Q

Chlamydia trachomatis has three different groups, causing different diseases. What disease do these serotypes cause?

A, B, C

D-K

L1, L2, L3

A

A, B, C - trachoma

D-K - cervicitis, urethritis, conjunctivitis, pneumonia neonates

L1, L2, L3 - lymphogranuloma venereum

33
Q

What is life cycle of chlamydia trachomatis?

A

Elementary body (EB) adapted for extracellular survival, binds to host receptor.

Endocytosis

Intracellular chlamydia differentiates intareticulate body, adapted for intracellular replication.

After replicaiton, some differentiate into EB, then released by cell to infect nearby cells

34
Q

How is chlamydia diagnosed?

A

Direct fluorscent antibody test DFA - smear of specimen stained with fluorescein conjugated monoclonal antibodies, viewed by UV microscopy

Rapid molecular test

35
Q

What is treatment of chlamydia infection?

A

Not susceptible to beta-lactams, which are used for gonorrhoea/syphilis. Which is why azithromycin is recommended when treating those conditions.

Azithromycin
Doxycycline

36
Q

What are causes of inguinal lymphadenopathy?

A 
Chancroid
Donovanosis
Gonorrhoea
Lymphogranulonum venereum
Syphilis
37
Q

What causes lymphogranuloma venereum, and what is its geographical spread?

A

Chlamydia trachomatis L1, L2, L3

Africa/ Asia/ SA
Occasionally occurs in other continents

38
Q

What clinical picture does LVG cause?

A

Primary ulcerating lesion at inguinal lymph nodes, which suppurates and discharge through skin

Can spread via lymphatics to cause systemic disease - fever, hepatitis, pnuemonitis, meningoencephalitis

39
Q

Diagnosis of LVG

Treatment LVG

A

Cell culture
Immunofluorescence
Nucleic acid tests

Doxycycline
Erythromycin

40
Q

Which bacteria causes chancroid?

What is clinical picture?

A

Haemophilus ducrei

Painful genital ulcers - as opposed to painless in syphilis

41
Q

What is treatment of chancroid?

A

Azithromycin/ erythromycin

Ceftriaxone

42
Q

Which bacteria causes donovanosis?

What is clinical picture?

A

Klebsiella granulomatis

Nodules on genitalia, which erode to form granulomatous ulcers that bleed on contact

43
Q

How is donovanosis diagnosed?

What is treatment?

A

Smear examination for itnracellular donovan bodies in cytoplasm of mononuclear cells

Azithromycin
Doxycycline

44
Q

Candida is normal commensal of vagina. At risk of infection if using oral contraceptivesm diabetes, antimicrobials, HIV.

How may it present if causing disease?

A

Irritant vaginitis
Cheesy vaginal discharge
Dysuria

45
Q

How is candida diagnosed?

What is treatment?

A

Microscopy and culture

Topical - clotrimazole
Oral - fluconazole

46
Q

Trichomonas vaginalis is protozoan parasite.

What is clinical picture?

A

Vaginitis with foul-smelling discharge

Men - often asymptomatic

47
Q

How is trichomonas diagnosed?

A

Wet preparation of vaginal secretions

Nucleic acid detection tests (NAT) used if microscopy negative in suspected patients

48
Q

What is treatment of trichomonas?

A

Metronidazole/ tinidazole

49
Q

When there is significant increase in gardnerella vaginalis, changes to enviroment allow increase in obligate anaerobes such as bacterioides - causing bacterial vaginosis

What are clinical criteria for diagnosing bacterial vaginosis?

A

Excessive vaginal discharge

Fish-smelling discharge

Vaginal pH >4.5

Presence of clue cells - vaginal epithelial cells coated in bacteria give it a stippled appearance

50
Q

What is treatment of bacterial vaginosis?

A

Metronidazole

51
Q

HSV-2 is most common cause of genital herpes - usually transmitted sexually.

But HSV-1 being detected more frequently, although usually cause oropharyngeal infection, and cold sores

What is clinical picture?

A

Ulcers start as vesicles, which break down to form painful shallow ulcers

Local lymphadenopathy

Usually heals in 2 weeks. But virus can travel up sensory nerve endings to establish latent infection in dorsal root ganglion neurones. It can then reactivate - genital cold sores.

Aspeptic meningitis can occur
Spread from mother to infant at time of delivery can give rise to disseminated herpes or encephalitis

52
Q

How is herpes diagnosed?

What is treatment?

A

HSV DNA from vesicle fluid or ulcer

Aciclovir
If recurrent - can take for 6-12 months, or take at start of symptom recurrence

53
Q

HPV has over 120 different types.

Which types are associated with cervical cancer?

Which types are associated with genital warts?

A

16 + 18 + 31. highly infectious. 40% of females infected two years after starting sexual activity

6 + 11 cause genital warts

54
Q

What is treatment of genital warts due to HPV?

What is treatment of cervical dysplasia due to HPV?

A

Podopyllin topically

Laser of loop excision

55
Q

Which primarily GI infections, can be transmitted “opportunistically” as STI?

Particularly in HIV patient

A

CMV
HAV
HBV

Cryptosporidiosis
Giardia
Entamoeba histolytica

Shigella
Salmonella

Usually during oral-anal contact

56
Q

What is treatment for pubic lice?

A

Permethrin cream

Malathion lotion

57
Q

Scabies can affect genital region. What is treatment?

A

Permethrin cream

IVermectin if immunocompromised

58
Q

What is differential diagnosis for vaginal discharge?

A 
Candida
Trichomonas
Bacterial vaginosis
Gardnerella
Chlamydia
Neisseria

Also consider foreign body, trauma, malignancy of cervix/ vagina, atrophic vaginitis

59
Q

Who is targeed in HPV vaccination program?

A

12-13 year old females
Recently extended to MSM

Targets HPV 6/11/16/18

60
Q

34 year old MSM presented with one dya history of painless ulcer on penis. Lesion firm and round. No rash, systemic symptoms or urethral discharge.

What is next test to perform?

Chlamydia NAAT
Dark ground microscopy on swab from lesion
Herpes simplex PCR
Light microscopy from lesion
RPR
A

Dark field microscopy - likely chancre from primary syphilis.

RPR may not detect antibody in early syphilis

HSV lesions likely to be painful, but important to sent swab for viral PCR

Chlamydia, particularly LGV serovars, can cause ulceration, but less likely

61
Q

23 year old pregnant women presents 28 week gestation, with two day history of painful genital ulcers. No previous history of any similar lesions. Swab taken reveals HSV2 by PCR

What test is most useful to assess risk of transmission to baby?

HSV DNA load of lesion
HSV DNA testing of blood
HSV susceptibility test for aciclovir
HSV antibody of her partner
HSV antibody on her booking blood
A

HSV antibody on her booking blood

Greatest risk to baby if primary infection occurs to mother during late trimester. There will not be time for mother to develop antibodies, so baby will not receive enough passive maternal antibodies to resist infection.

Testing booking sample can help determine primary or secondary infection.

Mother should receive aciclovir therapy to suppress virus until delivery.

Obstetric team will inspect genital area for lesions at time of delivery. If present, will advise C-section

62
Q

what are symptoms of congenital HSV2 infection?

A

Symptoms congenital -
- Localized skin infection–small, fluid-filled blisters on the skin and around the eyes and mouth that burst, crust over and heal

  • Encephalitis–an inflammation of the brain, which can cause problems with brain and spinal cord function, including seizures
  • Disseminated herpes infection–the most dangerous type of herpes infection. The herpes virus is spread throughout the body and can affect multiple organs, including the liver, brain, lungs and kidney.
63
Q

Mycoplasma genitalium (MGen) is second most common cause of STI after chlamydia

What symptoms can it cause?

What are risks in pregnancy?

A

Often asymptomatic

Urethritis

PID

In pregnancy - risk transmission to baby linked to preterm birth and miscarriage?

64
Q

How to diagnose mycoplasma genitalium?

Is not part of normal STI screen, despite being more common than gonorrhoea. If STI screen negative, and asymptomatic, then consider testing

A
  • Vaginal swab
  • First void urine sample
  • If positive, should prompt investigation for other STI/ HIV and contact tracing

Not blood test for mycoplasma pneumoniae CFT

65
Q

What is treatment for mycoplasma genitalium?

A

Doxycycline 100 mg twice daily for seven days

or
Azithromycin 1 g as a single dose, then 500 mg daily for two more days;

or
Moxifloxacin 400 mg daily for 10 days. This is currently reserved for cases known to be resistant to azithromycin. Resistance to moxifloxacin is already problematic in Asia.

Advise to refrain from sexual intercourse until finished treatment

66
Q

Which STIs are associated with sero-negative arthrpathy?

A

Chlamydia - strongest association

Gonorrhoea

Mycoplasma genitalium

Shigella

Medical Microbiology and Virology (60 decks)

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