Infection

Learning objectives

To understand how an infection develops

To learn about the main groups of pathogenic organisms

To introduce examples of pathogens

The life of an infection. (Try to explain the graph)

The main Pathogens (germs)

Bacteria: Prokaryotic organisms that reproduce inside the body and release toxins that harm the body.

Responsible for food poisoning, blood poisoning etc.

Bacteria contd.

Gram + cocci e.g. Staphylococcus aureus responsible for MRSA & Streptococcus pneumoniae responsible for pneumonia

Gram –ve cocci: the STD Gonnorhoea and bacterial meningitis

All treatable with antibiotics Penicillin

Various bacilli

Escherichia coli Harmless in our lower gut but causes sickness if ingested in food, Salmonella, cholera and bubonic plague.

Other bacterial disease

Clostridium spp. Cause Botulism (a serious type of food poisoning) and tetanus (lock jaw) a potentially fatal type of blood poisoning.

Tuberculosis

Leprosy (treatable but not curable) Also not very infectious

Syphilis – another STD

Lyme Disease – spread by a deer tick.

Viruses

Viruses

Very small

Cannot sustain life on their own

Must develop and reproduce as parasites in cells

Kill host cells

Hard to treat because they are protected by host cells.

Viral life cycle

http://www.wisc-online.com/Objects/ViewObject.aspx?ID=SCE404

Viral diseases

Mostly cannot be treated. Many can be prevented by vaccination.

Small Pox/ cow pox/chicken pox

Measles and german Measles (Rubella)

Mumps

Common cold, Influenza

HIV

norovirus and rotavirus, common causes of viral gastroenteritis

Wide a variety of different classes of virusesDepends on whether they have RNA and DNADepends on life cycle and how they reproduce inside the cellExample of viral classification, the chicken pox virus, varicella zoster (VZV), belongs to the order Herpesvirales, family Herpesviridae, subfamily Alphaherpesvirinae, and genus Varicellovirus. VZV is in Group I of the Baltimore Classification because it is a dsDNA virus that does not use reverse transcriptase.

Prions

These are simple infectious proteins

They can only reproduce inside animals where they convert existing proteins to the rogue form.

They are currently only known to cause diseases of the nervous system such as mad cow disease and Creuzfeld Jakob

Protozoans

Single celled Eukaryotes. Most are harmless but some are pathogens:

Amoebae: Amoebic dysentery

Flagellates

• The diarrhoea causing Giardia lamblia; Sleeping sickness Trypanosoma

Sporozoans:

• Malaria caused by Plasmodium

Toxoplasmosis

• Which can cause severe foetal deformities if it infects pregnant women.

Fungi

Athletes foot

Thrush

Other skin infections such as Jock itch and

ringworm

Infections of the toenail.

Multicellular parasites

• Helminthic diseases (caused by types of worms)

• Tapeworms: Pork or beef

Pork tapeworm in brain

Scolex of tapeworm that attaches to gut wall

Flukes: Schistosomiasis (liver flukes and blood flukes)

Nematodes: Various species affect the gastro-intestinal tract notably Ascaris Lumbricoides (Large Intestinal Roundworms)

Also cause Guinea worm

And Elephantiasis

Answer these questions

What things may cause infections?

Why does an infection take a while to develop?

Why does an infection make you ill?

Why do you get better from most infections?

Why might you not be able to catch the same infection again?

Homework• Find out about a disease causing organism and write about it. Your report

must contain the following:• A description of the disease causing organism (include a picture). (5 points)• A description of the symptoms of the disease – include information on

potential morbidity. (3 points)• Methods of treatment and prevention. (3 points)• Methods of transmission of the disease. (2 points)• Discovery of the disease causing organism. (1 point)• Regions of the globe and or sections of society most affected by it. (2 points)• You must not copy and paste! You must include references!• (English 3 points, refs 1 point)• Total 20 points

Alternative

In pairs develop a five minute presentation about one of the diseases named in this lesson:

MRSA, Gonnorhoea, Salmonella, Botulism, TB, Syphilis, Lyme Disease, Leprosy, HIV, chicken pox, mumps, measles, common cold, rota virus, creuzfeld jacob, athletes foot, amoebic dysentry, giardia, sleeping sickness, toxoplasmosis, pork tapeworm, liver flukes, schistosomiasis, ascariasis, guinea worm and elephantiasis.

Use guidance from homework slide to show what must be included in your presentation.