Post on 03-Jan-2016
Who gets them?
• Mammals and birds
• amphibians, reptiles and fish
• plants and fungi
• insects
• even bacteria are infected by viruses
“vertical transmission”
• Some viruses can cross the placenta
• Infection during pregnancy can damage the foetus
e.g. Rubella, Cytomegalovirus
Infection during first trimester:
Congenital infection syndrome:cataractsheart defectsmicro-cephaly mental retardationdeafness
Rubella:
After entry into the body:• Viral infections can
be localised, to the site of inoculation
• e.g.– Human
papillomaviruses - skin (warts)
http://hpvvirusinwomen.com/pictures-of-hpv.php
or the body surfacee.g. Rotavirus
Infantile gastro-enteritisFever, vomiting, diarrhea. dehydration, abdominal pain
http://www.gmchospital.com/newsletter/0711/rotavirus.php
http://newsatjama.jama.com/2013/01/24/vaccinating-infants-against-rotavirus-may-also-protect-adults/
Respiratory tract
e.g. Influenza
Virus replicates and is shed from the body surface, highly infectious
http://micro.magnet.fsu.edu/cells/viruses/influenzavirus.html
http://cbppatient.com/health-conditions/influenza/
Some examples of generalised viral infections:
http://www.npr.org/blogs/health/2011/05/27/136727069/your-health-podcast-doctors-misbehaving-and-measles-raging
Measles
http://summitpediatrics.blogspot.com/2011/04/measles.html
It starts out with cold-like symptoms for 2-4 days: cough, runny nose, fevers, body aches, and sometimes red, watery eyes or diarrhea. Then a red, bumpy rash develops and lasts for about 5-6 days.
http://vdsstream.wikispaces.com/Mumps
MUMPSspread among people through coughing and sneezingfever, headache, muscle aches, tiredness, loss of appetite, and swollen glands
Rabies
Motor neurone
http://news.bbc.co.uk/2/shared/spl/hi/health/03/travel_health/diseases/html/rabies.stm
Brain disease- once symptoms of rabies have developed the condition is almost always fatal
Cell surface receptor:
Factors required for virus replication
Virus receptor cell type
HIV CD4 T cellsEpstein-Barr CR2 B cellsInfluenza sialic acid many cell typesRhinovirus ICAM-1 many cell typesPoliovirus poliovirus receptor neuronsMeasles CD46 many cell typesHHV6-herpes CD46 many cell types
How do viruses cause disease?
1. by damaging/killing cells outright2. by inducing immuno-pathology 3. by transforming cells
cancer
…. by damaging/killing cells
e.g.Poliomyelitis• the virus is cytolytic• destroys motor neurons in the spinal cord,
and so causes paralysis
X-section of the spinal cord
showing severe inflammation of anterior horn cells
http://upload.wikimedia.org/wikipedia/commons/7/7e/Rooseveltinwheelchair.jpg
…. by inducing immunopathology
The patient’s T cells attack and destroy virus-infected cells
Inflammation and cell death
“Help!
T cell
by transforming cells cancer
• When a virus infects a cell, it expresses proteins that cause the cell to multiply and/or block apoptosis (programmed cell death)
• Cancer is multi-factorial: Oncogenic viruses are very common, only a small % of people infected actually get cancer
Major viral cancers
Copyright John Valentine DMD 1999
– Cancer of the cervix– Cancer of the liver– Certain leukemias &
lymphomas– Kaposi’s sarcoma
Viruses are involved in about 15% of human cancers:
Acute
Viral replication
Incubation periodViral replicationImmune responseClearanceimmunity
Virus replication in the body over time:
++++++++++symptoms
exposure
Role of Antibodies:
YYY
Neutralize extra-cellular virus
Protects from re-infection
Prophylaxis- prevention or protection from disease
Our immune response protects us from viruses:
T cells- group of white blood cell that rid the body of foreign invaders
Persistent infections:
HIVHepatitis CHepatitis B
++++++++ + + + + + + +symptoms
On-going replication: