S1: Virology of Sexually Transmitted Infections Flashcards
Describe the structure of HIV virus (Human Immunodeficiency Virus)
- 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
How does HIV enter cells?
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
How does HIV integrate into hosts DNA?
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
What happens once HIV integrates into host’s DNA?
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
How does HIV kill cells?
- 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
What are the clinical manifestations of HIV?
They are similar to normal illness
- General clinical manifestations
- Fever
- Lethargy
- Malaise (uneasy)
- Headache
- Sore throat
- Myalgia (muscle pain)
How long does it take for the onset of acute illness to occur from time of infection with HIV?
2-4 weeks
What are the symptoms of HIV?
- Rash
- Urticaria
- Loss of hair
- Ulcerations in mucocutaneous areas
- Headache
- Other neurological symptoms
- Gastrointestinal
- Diarrhoea
What are the lab based diagnoses for HIV?
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
Explain the general course of an herpes simplex virus
0-6 days
Vesicular pustile
6-12 days
Wet Ulcer
12-20 days
Dry crusts
What happens after the lesions have healed?
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
What does latency mean?
Virus replication stops and few virus proteins are made
What does reactivation mean?
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)
How is herpes simplex 1 transmitted?
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.
Do all individuals with HSV get recurrences?
Some individuals will not have any recurrences, while others may have over 15.
