Human viral disease

Who gets them?

• Mammals and birds

• amphibians, reptiles and fish

• plants and fungi

• insects

• even bacteria are infected by viruses

• Most viruses are species specific

• Most, but not all

And of course, in us humans…

Classification of human viruses

Source of infection:

Shedding virus susceptible

Man > 99%

animals zoonosis

Routes of entry:

sexual

Inhalation

inoculation

Bloodorgan t/plant

ingestion

Congenital / vertical

“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

Chicken Pox

Shingles

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:

Primary infection reactivation

++++++++++ +++

B Latency:

e.g. herpes simplex virus