Infectious diseases

What is a pathogen?

What is a pathogen?

Pathogen- from Greek pathos (emotion/suffering); gene – to give birth toAn agent causing illness or disease in the host/ an infectious particle able to produce disease

Are all pathogens infectious?

• Not necessarily

Infectious agents

• Pathogenic bacteria• Pathogenic viruses (not considered organisms)• Pathogenic fungi• Pathogenic protists (protozoa)• Pathogenic parasites – e.g. helminth worms• Pathogenic prion (not organisms)

What are the top ten infectious diseases?

10. Smallpox9. Typhoid

8. Influenza7. Bubonic Plague

6. Cholera5. Anthrax4. Malaria

3. SARS Coronavirus2. EBOLA or Nanta haemorrhagic virus

1. HIV

WHO

Non-specific defences: External Defences

Innate Immunity: commensal (non-pathogenic) bacteria

• Of the 100 billioncells in our bodies, only 10 billion are actually human cells!

• The rest are commensal bactseria, fungi, protozoa and even arhropods!

• They perform essential housekeeping functions in our bodies…

Summary of external defencesAnatomical Defences

– skin– mucous membranes

Body secretions/excretions– mucous– tears, saliva, urine (wash-out)– lysozyme in tears/nose/saliva– lactoperoxidase in breast milk– Acidic pH (sweat, urine,

gastric fluid, vaginal secretions)

– Zinc and spermine in semen

Normal commensal flora– Inhibitory substances– Compete for nutrients

CiliaMucociliary escalator in respiratory tract

Cells of the innate Immune System

• Phagocytes – monocytes, macrophages and neutrophils (polymorphonuclear neutrophils)

• Natural Killer Cells• Dendritic Cells

Phagocytes

Macrophages

Neutrophils

• Most common type of white blood cell (50 – 70%)

• Phagocytic – but die immediately!

• First immune cells to reach a site of infection – attracted by chemotaxis

• PUS is made of dead neutrophils (that’s what makes pus white…)

Phagocytosis (1)

Phagocytosis (2)

Natural Killer CellsThe NK releases "perforin" molecules onto the target

cell, which punches holes in its plasma membrane. The

NK cell then releases cytotoxins which will induce apoptosis (programmed cell

death) in the target cell. Nasty!! )

Dendritic Cells

A dendritic cell slide show…

• Dendritic Cells are beautiful...