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 virussusceptible Man > 99% animals zoonosis

Routes of entry: sexual Inhalation inoculation Blood organ 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: cataracts heart defects micro-cephaly mental retardation deafness Rubella:

After entry into the body: Viral infections can be localised, to the site of inoculation e.g. –Human papillomaviruses - skin (warts)

or the body surface e.g. Rotavirus Infantile gastro-enteritis Fever, vomiting, diarrhea. dehydration, abdominal pain accinating-infants-against-rotavirus-may- also-protect-adults/

Respiratory tract e.g. Influenza Virus replicates and is shed from the body surface, highly infectious s.html conditions/influenza/

Some examples of generalised viral infections: /your-health-podcast-doctors-misbehaving- and-measles-raging

Measles ml 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.

MUMPS spread among people through coughing and sneezing fever, headache, muscle aches, tiredness, loss of appetite, and swollen glands

Chicken Pox Shingles

Rabies Motor neurone h/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 Virusreceptorcell type HIVCD4T cells Epstein-BarrCR2B cells Influenzasialic acidmany cell types RhinovirusICAM-1many cell types Polioviruspoliovirus receptorneurons MeaslesCD46many cell types HHV6-herpesCD46many cell types

How do viruses cause disease? 1. by damaging/killing cells outright 2. 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

…. 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 period Viral replication Immune response Clearance immunity Virus replication in the body over time: symptoms exposure

Role of Antibodies: Y Y Y 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: HIV Hepatitis C Hepatitis B symptoms On-going replication:

Primary infection reactivation B Latency: e.g. herpes simplex virus