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Medical Microbiology > STI's > Flashcards

STI's Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Give examples of STI’s

A 
Herpes Simplex Virus 
Human Papilloma Virus
Molluscum Contagiosum
Hepatitis B Virus
Human Immunodeficiency Virus
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2
Q

What are the risk factors for STI’s?

A 
Young age for 1st sexual encounter
Unprotected sex
Rough / anal sex
Multiple sexual partners
Sex with prostitute
History of previous STI
Use of alcohol / drugs
Living in urban areas
Immunodeficiency
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3
Q

Describe the features of Herpes Simplex Virus

A

120 - 200nm diameter.
Icosahedral capsid.
Linear ds DNA (~150 kb)
Enveloped

Two antigenic types 1 and 2
50 - 70% homology, share several cross-reactive epitopes

Traditionally: HSV-1 infections above the belt
HSV-2 infections below belt

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4
Q

Describe the epidemiology of HSV-2

A

Major cause of genital ulcer disease worldwide
Highly infectious, lifelong infection
Often transmitted in absence of symptoms
Higher prevalence in developing world, urban areas and women

Seroprevalence - USA 13-40%

- Europe 7-15 %

	            - Sub-Saharan Africa, Caribbean 30-50%

HSV-2 infection is a co-factor for HIV transmission

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5
Q

Describe the pathology of HSV

A

Neurotropic virus -
Disease at site of inoculation
Infects epithelial cells
Short replication cycle
Destruction of basal cells of squamous epithelium
Formation of virus filled vesicles
Inflammatory response
Development of humoral and CMI – infection resolves
Severe protracted and disseminated disease in IS
Establishes latency in sensory ganglia

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6
Q

What is neonatal HSV?

A

Complication of maternal genital HSV
Transmission from infected birth canal
Disseminates in unprotected newborn

Primary Maternal HSV
70% mortality
Mainly encephalitis and meningitis

Recurrent Maternal HSV
Severe damage in 3%

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7
Q

How is HSV treated?

A

Acyclovir (Zovirax)

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8
Q

What is the mechanism of action of Acyclovir (Zovirax)?

A

Interferes with DNA polymerase to inhibit DNA replication via chain termination

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9
Q

What is HPV?

A

Human Papilloma Virus (HPV)

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10
Q

Describe the features of HPV

A

Family Papovaviridae
Genera Papillomaviruses

> 100 serotypes

55nm icosahedral ds DNA
Non-enveloped

72 pentamers of protein L1 (basis of current HPV vaccine)

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11
Q

Describe the features of genital HPV

A 
Widely distributed
Most common sexually transmitted virus
Infection may be - clinically apparent
			        -subclinical 
			        - latent
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12
Q

Give examples of low risk HPV

A

(HPV type 6 or 11)
Genital warts (condyloma acuminata)
Anal warts
Cervical dysplasia

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13
Q

Give examples of high risk HPV

A

(HPV 16,18,45 & 31)

Carcinomas of cervix, vagina, vulva, anus, penis & oropharynx

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14
Q

What is Cervical Intra-epithelial neoplasia (CIN)?

A

Cervical intra-epithelial neoplasia (CIN) is a term that describes changes in the squamous cells of the cervix.

CIN is not cancer, but may need treatment to stop cervical cancer developing. CIN is a pre-cancerous condition.

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15
Q

Describe the features of CIN

A

Most CIN arise from transformation zone

CIN graded 1, 2 or 3 (3 most severe)

Progression from CIN 1 to 2 is not inevitable

50% of all CIN lesions regress

Low risk - associated with condyloma and CIN I (HPV 6 & 11)

> 50% CIN 2 & 3 associated with HPV 16 & 18

> 90% invasive cancers associated with HPV 16 & 18

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16
Q

Describe the oncogenesis of HPV

A

Multifactorial process that involves the modification of cellular genes

17
Q

What are the risk factors for the oncogenesis of HPV?

A

Genetic susceptibility of host
Impaired cell-mediated immunity
Sex steroid hormones
Smoking

18
Q

Describe the features of the HPV vaccine

A

Recombinant virus-like particles based on HPV capsid protein L1
Elicits HPV-neutralizing antibody responses

Two vaccines available:
“Gardasil” (Merck) produced in yeast quadrivalent, protects against HPV 6,11, 16,18
“Cervarix” (GlaxoSmithKline) produced in baculovirus bivalent, protects against HPV 16 & 18

19
Q

How can HPV be detected and prevented?

A

Papanicolaou (“Pap”) smear
HPV DNA testing
In contrast to other STIs, condoms provide limited protection
Topical microbicides e.g. Carrageenan

20
Q

Describe the features of Molluscum Contagiosum

A

Poxvirus, genus Molluscipoxvirus
Large 200-300nm ds DNA
4 subtypes
Subtype not significant in pathogenesis

21
Q

What is the mechanism of disease for Molluscum Contagiosum?

A

Replicates in epithelial cells
Incubation 2-7 weeks
Characterized by 2 to 20 discrete, 5-mm diameter, flesh-coloured dome-shaped papules, with a dimpled centre
Self-limiting disease, resolves 6-12 months
Widespread, persistent atypical MC seen in AIDS

22
Q

What is hepatitis?

A

Inflammation of the lived

23
Q

What are the symptoms of hepatitis?

A 
Malaise
Anorexia
Nausea
Abdominal discomfort
Pyrexia (fever)
Pale stool/dark urine
Jaundice 
Myalgia & Arthralgia
24
Q

What are the various clinical outcomes of Hepatitis B Virus?

A

Adult -
0.5% fulminant hepatitis
95% recover
5% chronic carriers

Children
< 5 years 30% chronic carriers

Neonates
> 95 % chronic carriers
30-90% eventually develop cirrhosis/ liver cancer-HCC

25
Q

Describe HBV pathology

A

HBV not directly cytopathic

Immune response – major cause of symptoms

Enhanced immune response - fulminant hepatitis

Weak Immune response - symptoms mild but chronicity ensues

26
Q

How are HBV and Hepatocellular carcinoma (HCC) associated?

A

Lifetime risk of HCC in a chronically infected person is 10-25%

Accounts for:
50% of HCC cases worldwide
70-80% of HCC cases in endemic regions

27
Q

What are the proposed mechanisms of how HBV causes HCC?

A
  1. Direct models
    cis-acting sequences deregulate host growth genes
    or
    trans-acting factors interfere with cellular growth control
  2. Indirect models
    HBV-induced liver injury triggers host liver cell regeneration
    ~ increases probability of mutation and malignant transformation
28
Q

How can HBV be prevented?

A
  1. Hepatitis B specific immunoglobulin (HBIG)
  2. Hepatitis B vaccine
    Recombinant yeast- derived HBsAg
29
Q

How can HBV be treated?

A

Pegylated Interferon - immune modulator

Lamivudine, Adefovir, Entecavir (nucleotide analogue reverse transcriptase inhibitors)

30
Q

What is HIV?

A

Human immunodeficiency virus

31
Q

Describe the structure of HIV

A

HIV is different in structure from other retroviruses. It is roughly spherical with a diameter of about 120 nm.

It is composed of two copies of positive single-stranded RNA that codes for the virus’s nine genes enclosed by a conical capsid composed of 2,000 copies of the viral protein p24.

Medical Microbiology (13 decks)

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