Viruses Flashcards
How is the herpes varicella zoster virus transmitted?
What is the incubation period and what are the symptoms?
The virus can also infect what type of cell?
It is transmitted via breathing out infected droplets, which will infect if it makes contact with respiratory mucosal surfaces. The virus will replicate at the mucosal surfaces for 10-20 days causing fever before being transmitted to the blood where it causes a skin rash. Chicken pox also infects sensory ganglia, the genome remaining within the cell until stress signals activate it.
Describe how the influenza virus causes disease.
The influenza virus infects epithelial cells of the lung, which triggers an innate immune response. This is caused through interferons which trigger inflammation and fever. After this the acquired immune system targets and destroys the virus using antibodies. After one year the virus will have mutated enough to cause infection again.
Give some examples of DNA viruses.
Give some examples of positive sense RNA viruses.
Give some examples of negative sense RNA viruses.
Smallpox, herpes and adenoviruses.
Rhinoviruses.
Ebola virus
What are the three types of genome organisation in viruses?
What is the coding capacity of viruses? Give an example.
Linear,
Circular,
Segmented (multipartite).
They have a low coding capacity, smallpox has a large genome of 130-375kb but only codes for 110-200 genes. Polio has a 7-8kb genome and codes for 12 genes.
How do interferons inhibit viral movement?
They induce an antiviral state in neighbouring uninfected cells. Mice engineered to lack interferons are more susceptible to viral infection.
How are RNA viruses detected by host cells?
RNA viruses make double stranded RNA which is not normally made by cells. Cells do not make DNA from RNA, but they make RNA from DNA. Viral nucleic acid is detected by toll like receptors or RNA helicase proteins which activate the cell.
Once interferons bind to neighbouring cells what occurs?
How do + sense RNA viruses prevent detection?
They bind to interferon receptors, the effectors of which slow virus replication and provide innate immunity and an antiviral state.
The replicase proteins of + strand viruses are targeted to the membrane. Here is where replication occurs with the replicase proteins assembling to make membrane spheres that prevent detection of the viral RNA.
Describe arenaviruses.
This a family of viruses that cause haemorrhagic fever that is often fatal. Signs and symptoms include fever and bleeding, flushing of the face and chest, petechiae (capillary rupture), Edema, shock and hypotension. Malaise, headache, muscle pain, diarrhoea and vomiting are also frequent symptoms. These viruses are transmitted by rodents.
How can viruses jump species barriers?
Through single amino acid mutations in some cases, but there must be close contact (urbanisation) for this transfer to take place. These mutation affect viral glycoprotein which allows it to bind to tyrosine 211.
To prevent the same structure of antibody being produced what is employed?
Viruses generate errors to what probability?
VDJ recombination causes gene rearrangements in the variable region of antibodies, this causes antibody diversity.
1 error per 100000 base pairs.
How do adenoviruses suppress immune responses?
They produce early and late genes. The early genes encode E3 19k, which prevents recognition of the infected cell by T cells. The protein binds to the peptide binding pocket of Major Histocompatibility Complexes class 1.
Karposi’s Sarcoma-associated herpes Virus possesses several genes with homologies to host proteins involved in immune responses, where do these come from?
The virus is a DNA virus therefore it obtains them via recombination with the host cell genome. Viruses can steal immune genes and use them in defence of itself. For example, viruses can make decoy receptors and ligands to block signal transduction.
What are the benefits to early HIV diagnosis?
Treatments such as HAART available.
Prophylaxis against opportunistic infections if appropriate.
Appropriate investigations if unwell.
Reduced perinatal transmission.
Minimising risk of infecting others.
Relief of anxiety about knowing HIV status.
What is the infection progress of HIV?
CD4 counts decline and HIV load increases,
There is an increased risk of developing infections and tumours,
The severity of these illnesses increases the lower the CD4 count is,
Most AIDs diagnoses occur at CD4 count
Approximately 30-60% of patients have what approximately 4 weeks post exposure.
A seroconversion illness. The symptoms are generally non-specific but may include: a flu-like illness, fever, malaise and lethargy, pharyngitis, profound damage to the immune system, toxic exanthema and lymphadenopathy.
