S1: Virology of Sexually Transmitted Infections Flashcards

1
Q

Describe the structure of HIV virus (Human Immunodeficiency Virus)

A
  • Has an envelope with viral proteins on the the envelope
  • Important viral proteins are glycoprotein 120 and glycoprotein 41
  • Host cell proteins are found on the envelope
  • Viral nucleic acid is RNA and there are 2 copies
  • Important proteins include reverse transcriptase, integrase, protease
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2
Q

How does HIV enter cells?

A

HIV binds to the CD4 receptor on CD4+ T-helper cells - another receptor called chemokine receptor is also used

The viral protein used for attachment is glycoprotein 120.

Then glycoprotein 41 changes shape and helps the virus fuse with the cell membrane

The virion then enters the cell ans loses its envelope

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3
Q

How does HIV integrate into hosts DNA?

A

First, HIV gets into hosts cell and loses its envelope

Viral RNA is reverse transcribed into DNA, and complementary DNA (cDNA) is made.

The cDNA is made into a double stranded copy that becomes circular and travels to the nucleus

It then integrates into the hosts DNA

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4
Q

What happens once HIV integrates into host’s DNA?

A

Viral messenger RNA is made in the nucleus and it is translated into proteins in the cytoplasm. The virus capsid is made and some proteins are glycosylated.

It then travels to the cytoplasmic membrane and buds off - a new HIV particle is made

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5
Q

How does HIV kill cells?

A
  • HIV mainly infects T-helper cells

There are cells that function as assistants to Th cells and these are antigen presenting cells and they bring the antigen to the Th cells attention

The Th cells their T cell receptors to touch and recognise these antigens

Once they recognise the antigens, the Th cells make interleukins IL-2. They also make interleukin receptors and cell is said to be activated

In activated cells, the virus replicates fast and viral proteins are made fast ultimately leading to cell death

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6
Q

What are the clinical manifestations of HIV?

A

They are similar to normal illness

  • General clinical manifestations
  • Fever
  • Lethargy
  • Malaise (uneasy)
  • Headache
  • Sore throat
  • Myalgia (muscle pain)
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7
Q

How long does it take for the onset of acute illness to occur from time of infection with HIV?

A

2-4 weeks

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8
Q

What are the symptoms of HIV?

A
  • Rash
  • Urticaria
  • Loss of hair
  • Ulcerations in mucocutaneous areas
  • Headache
  • Other neurological symptoms
  • Gastrointestinal
  • Diarrhoea
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9
Q

What are the lab based diagnoses for HIV?

A

Polymerase chain reaction (PCR) which is used to amplify RNA. Scientists are looking for viral DNA to be present

Look for viral proteins

Look for antibodies (IgM is patient has come early with symptoms , IgM may disappear after 3 months)

  • IgG if no IgM
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10
Q

Explain the general course of an herpes simplex virus

A

0-6 days
Vesicular pustile

6-12 days
Wet Ulcer

12-20 days
Dry crusts

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11
Q

What happens after the lesions have healed?

A

There is establishment of the latent infection in the dorsal root ganglia innervating the mucosal areas involved in acute infection

In other words…
The virus is on the skin until it migrates up inside the axon to the dorsal root ganglion. Then, at any time, the virus can start replicating again and migrates back down the axon towards the skin where it causes a recurrent infection

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12
Q

What does latency mean?

A

Virus replication stops and few virus proteins are made

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13
Q

What does reactivation mean?

A

There is release of the latent virus from the infected ganglia, this causes infection of the epithelial cells, leading to a recurrent infection (clinical or subclinical)

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14
Q

How is herpes simplex 1 transmitted?

A

You can get infected with herpes simplex 1, even if you only have one sexual partner, the more sexual partners the higher the risk of infection with HSV-1.

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15
Q

Do all individuals with HSV get recurrences?

A

Some individuals will not have any recurrences, while others may have over 15.

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16
Q

Explain the structure of Herpes Simplex Virus (type 1 and 2)

A
  • They are enveloped
  • There is an nucelocapsid inside the envelope made of capsomeres. The nucleocapsid has a icosaherdral structure.
  • There is a tegument between nucleocapsid and envelope.
  • The nucleic acid is a double stranded DNA virus and the DNA is linear (not circular)
17
Q

What are the lab based diagnosis for HSV?

A

Virus culture (with human cells) and HSV has a short replication cycle so there is rapid spread in the culture and destruction of cells –> this may take a few days to occur and get the diagnosis

More urgent diagnosis–> immunofluorescence labelling of infected cells can be used.
This is done by culturing a viral sample and then use of fluorescent labelled antibodies which are directed against the viral proteins. Hence, the viral proteins can be seen under a fluorescent microscope.

18
Q

Explain HSV replication

A

The virus attaches to the cell epithelium using specific receptors (which ones are uncertain) and there is fusion of the viral envelope with the cell envelope.

It penetrates into the cell losing its envelope in the process with the nucleocapsid entering the cell.

There is the transport of the nucleocapsid through the cytoplasm to the nucleus. The viral DNA is then released into the nucleus and becomes circular. There is then replication of viral DNA in the nucleus and mRNA is generated

Translation of the mRNA takes place in the cytoplasm. The capsids are transported back to the nucleus and DNA is packaged into the empty capsid.

The nucleocapsid containing DNA buds through the inner lamella of the nuclear membrane and then virus then agresses through the cell

19
Q

Explain the structure of Hepatitis B

A
  • There are complete viral particles and incomplete viral particles
  • The incomplete particles are surface antigen proteins (that lack a core) so can be found in the serum of infected individuals
20
Q

What are the clinical and epidemiological features of Hep B?

A

Incubation (days) – 35 to 150, mean is 75
Onset can be insidious or acute
Age preference is young adults, babies and toddlers
Transmission can’t be foecal-oral
Transmission can be percutaneous (e.g. needles), perinatal (from mother-baby), or sexual

21
Q

How is Hep B diagnosed?

A
  • Looking for viral antigens in serum

- Testing antibodies to viral proteins

22
Q

How can Hep B be transmitted?

A

Heterosexual activity, Transfusion or dialysis
Homosexual activity -Health care Employment
Household contact
Intravenous drug use Perinatal (mother to baby)

23
Q

Name some areas that are high risk in the world for Hep B

A

Africa

Indonesia

24
Q

What has caused Hep B numbers to go down?

A

Hep B immunisations
Introduction of testing
New treatment