STI's Flashcards
Give examples of STI’s
Herpes Simplex Virus Human Papilloma Virus Molluscum Contagiosum Hepatitis B Virus Human Immunodeficiency Virus
What are the risk factors for STI’s?
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
Describe the features of Herpes Simplex Virus
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
Describe the epidemiology of HSV-2
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
Describe the pathology of HSV
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
What is neonatal HSV?
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%
How is HSV treated?
Acyclovir (Zovirax)
What is the mechanism of action of Acyclovir (Zovirax)?
Interferes with DNA polymerase to inhibit DNA replication via chain termination
What is HPV?
Human Papilloma Virus (HPV)
Describe the features of HPV
Family Papovaviridae
Genera Papillomaviruses
> 100 serotypes
55nm icosahedral ds DNA
Non-enveloped
72 pentamers of protein L1 (basis of current HPV vaccine)
Describe the features of genital HPV
Widely distributed Most common sexually transmitted virus Infection may be - clinically apparent -subclinical - latent
Give examples of low risk HPV
(HPV type 6 or 11)
Genital warts (condyloma acuminata)
Anal warts
Cervical dysplasia
Give examples of high risk HPV
(HPV 16,18,45 & 31)
Carcinomas of cervix, vagina, vulva, anus, penis & oropharynx
What is Cervical Intra-epithelial neoplasia (CIN)?
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.
Describe the features of CIN
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
Describe the oncogenesis of HPV
Multifactorial process that involves the modification of cellular genes
What are the risk factors for the oncogenesis of HPV?
Genetic susceptibility of host
Impaired cell-mediated immunity
Sex steroid hormones
Smoking
Describe the features of the HPV vaccine
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
How can HPV be detected and prevented?
Papanicolaou (“Pap”) smear
HPV DNA testing
In contrast to other STIs, condoms provide limited protection
Topical microbicides e.g. Carrageenan
Describe the features of Molluscum Contagiosum
Poxvirus, genus Molluscipoxvirus
Large 200-300nm ds DNA
4 subtypes
Subtype not significant in pathogenesis
What is the mechanism of disease for Molluscum Contagiosum?
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
What is hepatitis?
Inflammation of the lived
What are the symptoms of hepatitis?
Malaise Anorexia Nausea Abdominal discomfort Pyrexia (fever) Pale stool/dark urine Jaundice Myalgia & Arthralgia
What are the various clinical outcomes of Hepatitis B Virus?
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
Describe HBV pathology
HBV not directly cytopathic
Immune response – major cause of symptoms
Enhanced immune response - fulminant hepatitis
Weak Immune response - symptoms mild but chronicity ensues
How are HBV and Hepatocellular carcinoma (HCC) associated?
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
What are the proposed mechanisms of how HBV causes HCC?
- Direct models
cis-acting sequences deregulate host growth genes
or
trans-acting factors interfere with cellular growth control - Indirect models
HBV-induced liver injury triggers host liver cell regeneration
~ increases probability of mutation and malignant transformation
How can HBV be prevented?
- Hepatitis B specific immunoglobulin (HBIG)
- Hepatitis B vaccine
Recombinant yeast- derived HBsAg
How can HBV be treated?
Pegylated Interferon - immune modulator
Lamivudine, Adefovir, Entecavir (nucleotide analogue reverse transcriptase inhibitors)
What is HIV?
Human immunodeficiency virus
Describe the structure of HIV
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.
