STIs

Question 1

Neisseria

Answer 1

Aerobic gram negative cocci
Oxidase and catalase +
N. meningitidis = meningitis
N. gonorrhoeae = gonorrhea
All look the same under the microscope
We are all colonized by some non-pathogenic species

Question 2

N. gonorrhoeae
(gram stain, shape, oxidase, catalase, intra/extracellular, media it grows on, transmission, what epithelia does it infect)

Answer 2

Aerobic gram negative diplococci
Oxidase and catalase +
Often appears intracellular on gram stain
Very fastidious (will not grow on SBA, may not survive drying and dies rapidly during transport)
Grow on Thayer Martin media
Transmission from male to female more likely
Primarily infects columnar or cuboidal epithelium

Question 3

Superoxol Test

Answer 3

Performed with 30% H2o2

Really bubbly

Question 4

One way to tell between gonorrhea and chlamydia

Answer 4

GC: copius discharge
C: no discharge

Question 5

2 major virulence factors for N. gonorrhoeae

Answer 5

1. Pili (adherence to mucosal surfaces, inhibit killing by neutrophils)
2. Outer membrane (facilitate invasion, has endotoxin)

Question 6

Sensitivity

Answer 6

The proportion of actual POSITIVES that are correctly identified as positive

Question 7

Specificity

Answer 7

The proportion of NEGATIVES that are correctly identified

Question 8

Positive predictive value

Answer 8

Proportion of patients with positive test results who are correctly diagnosed
Depends on the prevalence of the disease

Question 9

Negative predictive value

Answer 9

Proportion of patients with negative test results who are correctly diagnosed

Question 10

Gonorrhoea culture/diagnosis

Answer 10

Grows on chocolate agars with antibiotics (nutritous medial
Take urethral swabs from male and cervical swabs from females
Does NOT grow on SBA

Question 11

GC culture vs PCR samples for males and females

Answer 11

Culture: males use urethral swabs, females need cervical swabs
PCR: males need 1st voided urine, females need vaginal swabs

Question 12

What do we use to treat GC?

Answer 12

800mg Cefixime or 250mg ceftriaxone intramuscularly

Both are cephalosporins

Question 13

3 primary Chlamydia pathogens

Answer 13

C. psittaci (resp tract infections from birds)
C. pneumoniae
C. trachomatic

Question 14

Chlamydia life cycle

Answer 14

Biphasic
Elementary bodies (infective form) attaches to host cell, endocytosed, morphs into reticulate body (undergoes multiplication by binary fission), then differentiates back to elementary body, released from cell, on to infect others

Question 15

Chlamydia causes __ in men vs women

Answer 15

Men: urethritis
Women: cervicitis and PID

Question 16

Lab Diagnosis for Chlamydia (4)

Answer 16

Antigen detection
Immuno-fluorescence
Cell culture
PCR

Question 17

Chlamydia treatment (1st and 2nd line)

Answer 17

1st line: 1 gram Azithromycin (4 pills, single dose)

2nd line: 100 mg BID doxycycline (2 doses a day for 10 days)

Question 18

Haemophilus ducreyi

Answer 18

Produces Chancroid lesions
Tender, non indurated irregular ulcers
Infection is localized, but frequently spreads to regional lymph nodes
Lymph nodes enlarged and painful
Intra or extracellular bacteria, appear as cocco-bacilli or short rods
Gram varibale
Arranged in parallel chains (school of risk or rail road track appearance)
2 hotspots: Nairobi and Winnipeg
Fastidious - grows slowly on chocolate but using 2 media is optimal

Question 19

Media for H. ducreyi

Answer 19

Gonococcal agar based or a Mueller Hinton based medium can be used, and add:
1% IsoVitalex, 5% chocolatized horse blood or 1% hemoglobin, 5% fetal calf serum, Vanco

Question 20

Molluscum contagiousum

Answer 20

Large enveloped DNA, poxvirus family
Only found in humans (no animal reservoir)
Diagnosis: EM, clincal appearance, PCR
Not painful but can be itchy (can lead to secondary infections and scarring)
Affects any area of the body
High incidence in children, immunocompromised, sexually active adults
Transmitted through direct contact and fomites
Long incubation period and lasts a long time, but will go away on its own (does not stay in body)
Treat with chemical or surgical removal of lesions

Question 21

Clinical appearance of Molluscum contagiousum

Answer 21

Flesh coloured lesions
Dome-shaped with dimpled center
Diameter 1-5 mm

Question 22

Herpes simplex virus

Answer 22

Enveloped, icosahedral capid, dsDNA
Thymidine kinase and DNA polymerase (acyclovir)
Spectrum of disease: asymptomatic, lesions, encephalitis, recurrent meningitis, ocular infections

Question 23

HSV 1 versus HSV 2

Answer 23

1: frequently associated with oral/ocular infections (rising in cases of genital herpes though) - less reoccurrences, less asymptomatic shedding
2: most frequently associated with genital infections

Question 24

Molleret’s

Answer 24

Meningitis from herpes
Recurrent
Will go away on its own without treatment

Question 25

Latency and Reactivation of herpes

Answer 25

1. Local replication and entry of virus into cutaneous neurons 2. Centipetal migration in the axon 3. Reactivation and replication 4. Centrifugal migration to the epidermis

Question 26

Melt curve analysis

Answer 26

Way to diagnose herpes Real time PCR Uses the primers for both 1 and 2 and based on what temperature they probes melt off you can generate a melting temperature which is characteristic for one of them

Question 27

Acyclovir

Answer 27

Nucleoside analog - chain terminator Blocks viral DNA polymerase Has to be phosphorylated to be activated First activation with HSV thymidine kinase, next 2 with host enzymes

Question 28

Human Papilloma Virus

Answer 28

Papillomaviridae Non-enveloped, dsDNA virus Most prevalent STD Cannot be grown in culture - molecular detection possible and use Pap test Oncogenic virus Contact transmission Acquisition shortly after onset of sexual activity

Question 29

Respiratory papillomatosis

Answer 29

Benign warts in the upper airway (may cause obstruction, can surgically remove) Caused by HPV 6 and 11

Question 30

Treating genital warts

Answer 30

Usually for aesthetic reasons Podophyllin resin, trichloroacitic acid, cryotherapy Burn or freeze them off

Question 31

Why are only some HPV strains oncogenic?

Answer 31

High risk HPV has a circular gene Gets integrated into the genome and splits a gene that regulates expression of E6 and E7 These have effects on the cell that will lead to its proliferation

Question 32

E6 vs E7

Answer 32

E6: binds and leads to degradation of p53 (low risk types do NOT bind p53) E7: binds the retinoblastoma TSG product so the transcription factor is free to activate the cell cycle (low risk types bind poorly to this)

Question 33

Gardasil vs Cervarix

Answer 33

G: Types 16, 18, 6, 11 C: Types 16, 18 only

Question 34

HPV L1 Virus-Like-Particle Vaccine

Answer 34

``` Give a pseudovirus from the capsid proteins Very safe (no replication) ```