Viral STIs Flashcards
What kind of virus is Molluscum contagiosum?
A large enveloped DNA poxvirus
What/who is the reservoir for M. contagiosum?
humans, no animal reservoir
What is the clinical presentation of Molluscum contagiosum? (2 symptoms)
- Flesh coloured lesions
- Dome shaped and have a dimpled centre
- 1-5 mm wide - Itchiness but not usually painful
What is the usual method of diagnosis of M. contagiosum?
visual identification
- you could submit PCR or do EM but it’s unnecessary
What can happen if you scratch at the M. contagiosum lesions?
then you can spread them to other parts of the body
What tissues does M. contagiosum infect?
Skin and mucous membranes anywhere on the body
What 3 populations of people are at higher risk of contracting M. contagiosum?
- Children (ages 1-10)
- Immunocompromized people
- Sexually active adults*
What are 3 modes of transmission for M. contagiosum?
- Skin to skin contact
- Sexual contact
- Indirect via fomites (clothing or towels)
What is the incubation period for M. contagiosum?
2-7 weeks
How long is a person infectious with M. contagiosum?
until the lesions have cleared
How long does M. contagiosum take to resolve typically?
6-8 weeks
What should be avoided with M. contagiosum to let it clear? what can be the result?
Shaving should be avoided to prevent bleeding and autoinoculation/spread
What happens once the lesions clear? is there established immunity/latency?
No latency, MCV clears (unlike HSV) but there is also no permanent immunity so you can be infected again
What treatments are there for M. contagiosum?
no antivirals
you can burn off or surgically remove the lesions
What kind of morphology do the herpes viruses have?
enveloped icosahedral
What kind of genome do the herpes viruses have?
dsDNA
What are two enzymes that are unique to HSV?
- Thymidine kinase
2. viral DNA polymerase
What is HSV (HHV) 1 most often associated with?
oral/ocular infections
HSV(HHV)-2 is most commonly associated with?
Genital infections
What has changed recently in the epidemiology of HSV-1?
now is causing more genital infections
Which form of HSV can cause a self limiting type of meningitis? what is it called?
HSV-2 can cause Molleret’s meningitis
What are the 3 stages of a herpes virus infection?
- primary infection
- latency
- reactivation
What % of primary infections are asymptomatic?
80-90%
When do primary infections tend to occur? where?
Generally occur between the age of 6 months and 3 years of life
Infection via oral, genital, ocular epithelium or breaks in skin
Where are the locations of latent infection for HSV-1 and HSV-2? what kind of migration occurs from the epidermis to the ganglia?
HSV-1 = trigeminal ganglia HSV-2 = dorsal root ganglia
centipetal movement towards the ganglia along the axon
what occurs during reactivation of an HSV infection? what kind of movement is this?
virus can reactivate, multiply in the nerve cell and be transported along the axon to the nerve terminals in the skin
- centrifugal movement to the epidermis
What are two triggers for an HSV reactivation?
Immunosuppression and stress
For people infected with HSV-1 how many recurrences are there in the 1st year? how common is asymptomatic shedding?
usually less than 1 in the first year
asymptomatic shedding is uncommon
For HSV-2, how common is asymptomatic shedding? what % of people have a recurrence in the first year?
90% have 1 reoccurrence/year
Asymptomatic shedding has been shown to occur on 28% of days
When would someone be given acyclovir? Does it prevent asymptomatic shedding?
If someone presents with lots of recurrences a year
No acyclovir doesnt
What is the lab diagnostic method of choice for diagnosing HSV?
RT-PCR with melt curve analysis
How does melt curve analysis work?
The temp at which the primer will melt off of the sequence (and expose fluorochorme?) will tell you what virus you have
Review: what accomplishes the first step of acyclovir activation?
Viral thymidine kinase (phosphorylation)
What are the rates of acyclovir resistance in competent vs. immunocompromised people?
0.1 in competent
4-7 in immunocompromised
What is the more common source of acyclovir resistance?
Thymidine kinase (TK) mutants (95%) Viral DNA polymerase (5%)
What are two alternate drugs to acyclovir? How do they work?
Cidofivir = phosphorylated nucleotide analog (doesn’t need TK)
Foscarnet = pyrophosphate analog (blocks viral DNA polymerase)
What family of viruses does human papilloma virus belong to?
Papillomaviridae
What kind of genome/structure does HPV have?
dsDNA virus
non-enveloped
What % of adults are infected with HPV?
80%
Can HPV be grown in culture?
no
What are two methods of testing for HPV?
- Molecular detection possible
2. Papanicolaou test (Pap test or Pap smear)
What are the two types of HPV? How are they contracted?
High (through sexual contact) and low (dermal type) risk
What 3 things are high risk HPV associated with?
Cervical cancer, Head and neck cancer, other anogenital cancers
What 2 things are low risk HPV associated with?
- recurrent respiratory papillomatosis
2. anogenital warts
What are the two important serotypes of high risk HPV?
16 and 18
What are the two important serogroups for low risk HPV?
6, and 11
What types of symptoms are congruent with a skin to skin (contact) transmission of HPV?
plantar, common and flat warts
What is respiratory papillomatosis?
Benign warts in the upper airway that can cause airway obstruction
What can be done to treat respiratory papillomatosis?
surgical removal
What serotypes cause respiratory papillomatosis? When is it acquired?
6 and 11
Childhood - usually acquired at birth
Adult acquisition - usually related to oral intercourse
What are 3 treatments for genital warts?
- Podophyllin resin
- Trichloroacitic acid
- Cryotherapy
When does infection with HPV normally occur? Can multiple co-infections occur?
Typically very shortly after onset of sexual activity
Co-infections can occur, pretty common
How long do individual episodes of infection with HPV last? What occurs in the majority of people?
4-20 months
Most often it is a transient infection that the immune system clears. Reappearance of the same type is uncommon
- only a small subset of people continuously shed the virus
HPV 16 and 18 are associated with what % of cervical cancer?
75%
In women, infection with HPV 16 or 17 will lead to formation of first…
precancer or high grade precursors and then full blown cervical cancer
What is detected on a PAP test?
Detection of patients with cervical cells abnormalities
- Atypical squamous cells of unknown significance (ASCUS)
What results in some HPV strains being oncogenic while others are not? What is increased in expression?
Disruption/deletion E2 transcriptional repressor leads to them having a selective growth advantage and later cancer
Increased expression of E6 and E7
What is the role of E6? how is this different in the low risk types?
Binds and leads to degradation of p53 (tumor suppressor)
HPV E6 from low risk types do not bind p53 or don’t result in degradation
What are the two HPV vaccines and how are they different?
- Gardasil - quadrivalent (against 6, 11, 16 and 18)
2. Cervarix (16 and 18 only)
