Viruses - what they are and pathogenesis Flashcards
attributes of viruses
They can replicate in hours
They replicate to very high numbers
They have error-prone polymerases (particularly RNA polymerases)
Viruses generate a lot of variants. Most of these are unfit, but some are able to escape existing immunity
A wide range of immune responses is needed to deal with them
You can’t possibly have antibodies and T cells against everything you will be exposed to
Two ways that a virus can leave the cell
They can cause lysis – causing damage to host as they leave
Form an envelope from the host membrane to cause budding – non cytopathic
Common virus diseases of man
Influenza Common cold Measles Mumps Chicken pox/Shingles Glandular fever Hepatitis Papillomas (Warts) AIDS Kaposi’s sarcoma
Diseases that may have viral aetiology
Multiple sclerosis Schizophrenia Type I diabetes Myalgic encephalitis (chronic fatigue syndrome) Other cancers (colorectal)
General patterns of viral infection
Acute infection
Latent, reactivating infection
Persistent infection
Acute Infections - a huge spectrum of disease and range of outcomes
Mumps (Paramyxovirus) Measles (Paramyxovirus) Calicivirus (Norwalk-like) Rotavirus (Reoviridae) Poliovirus (Picornaviridae, enterovirus) SARS (Coronavirus) Ebola Smallpox Colds (rhinovirus) Flu
Latent/reactivating infections - Human Herpes Viruses
Herpes simplex virus type 1 Herpes simplex virus type 2 Varicella zoster virus (3) Epstein-Barr virus (4) - glandular fever, kissing disease Cytomegalovirus (5) Human herpesvirus 6 Human herpesvirus 7 Human herpesvirus 8
Life-long infection, controlled by immunity
Herpes simplex virus type 1
Primary Gingivostomatitis as a child
Cold Sore when you are older and immune system is weak
Varicella zoster virus (3)
chickenpox as a child
possible shingles during reactivation as an adult, appears in very defined sectors
Herpes Simplex & VZV latency
Retrograde axonal transport involving microtubules to neuronal nucleus
These viruses have ways to evade the immune system, they will hide in dorsal ganglion and go into latency not presenting antigens to present to your immune system.
Common trigger of cold sore is immunosuppression event, older people get shingles because if immunosuppression, it goes back down the nerve, it affects the area that is innervated by that dorsal root ganglia
Persistent Infections in the absence of an active immune response
First, a virus that gets in to an animal to cause immunotolerance where it doesn’t cause an immune response
HIV - retrovirus
HCV - flavivirus
Get a peristent virus that is controlled by the immune system
Bovine Viral Diarrhoea Virus
Usually a classical acute infection; makes the animals sick and immunosuppressed for a couple of weeks; symptoms very much like foot-and-mouth
Virus can be spread by aerosols and faeces
Reservoir of virus is a small pool of persistently infected animal.
These animals acquire the virus as foetuses before the development of the adaptive immune response, in a largely asymptomatic infection.
These animals see the virus as self!
These animals constantly shed the virus.
Eventually the virus in these animals mutates and generates a cytopathic virus that kills the animal because they do not see the virus as foreign.
How does virus infection of a host lead to disease?
Many infections are apathogenic or associated with relatively mild symptoms; it is important to realize that from the virus’ point of view these are not always failed or resolved infections – a successful virus is one that replicates well enough to spread to the next host.
Pathogenesis results from cell tissue damage cause by viral infection usually lysis of cell - caused by cytopathic viruses
Cytopathic damage: EBOLA targets Vascular Endothelial Cells
Ebola targets endothelial cells
The receptor is only on endothelial cells hence why affects it only
Causes lysis of them
Therefore causes massive blood vessel leakage, blood in the skin and organs -> organ failure
Cytopathic damage: Influenza A virus targets lung epithelia
Lack of cilia - inabillity to effectively clear infection
