Unit 4 – Immunology and Public Health

Infectious Disease and Epidemiology

Learning Intention:

To learn about infectious diseases and epidemiology

Success Criteria:

By the end of the lesson I should be able to

• State that infectious diseases can be transmitted by direct physical contact, water, food, body fluids, inhaled air or vector organisms.

• State that infectious diseases can be controlled b quarantine, antisepsis, vector control, individual responsibility (e.g. good hygiene, care in sexual health, appropriate storage and handling of food) and community responsibility (e.g quality water supply, safe food webs, appropriate waste disposal systems).

• Describe the following spreads of disease:– Sporadic (occurring occasionally)– Endemic (regular cases occurring in an area)– Epidemic (unusually high numbers of cases in an area)– Pandemic (a global epidemic)

• Describe disease control measures to include preventing transmission, drug therapy, immunisation or a combination of these.

Infectious Disease

• Infectious diseases are caused by pathogens such as – viruses, (e.g. measles)– bacteria, (e.g. cholera)– fungi, (e.g. athlete’s foot)– protozoa (e.g. malaria)– multicellular parasites (e.g. hookworm)

BacteriaBacteria are single-

celled organisms and can cause diseases such as:

- Cholera- Typhoid- Salmonella- Pneumonia- Tuberculosis

Case Study - How do malaria, sleeping sickness, influenza, TB and HIV evade the host

immune response? What do we need to know?

1. Background on the disease –

· cause (virus, protozoa, fungi, bacteria)

· transmission

· epidemiology

2. How it evades the hosts immune system

· Antigenic variation or direct attack?

· Explain the method using the chosen disease as an example

3. How are scientists trying to combat these diseases if they can evade the immune system?

VirusesA virus can only survive

outside a host for a very short time, however they are responsible for many diseases;

- AIDS- Chicken pox- Influenza- HerpesAnd some cases of cancer,

e.g. Cervical cancer caused by the Human papillomavirus (HPV)

Fungus

Fungi are widely used by humans but some can cause diseases like:

- Thrush

- Ringworm

- Athlete’s Foot

Protozoa

Protozoa are single-celled organisms which are typically mobile. They can cause:

- Malaria

- Sleeping sickness

- DysenteryMalarial infestation by Plasmodiumhttp://www.youtube.com/watch?v=OEDhe4MPEMc

Multicellular parasites

Multicellular parasites include tapeworms and hookworms (pictured).

They can cause

- Anaemia

- Diarrhoea

- Low birth weightShort clip of tapeworms in situhttp://www.youtube.com/watch?v=JeDD0HdecGk

Pathogen Transmission

These pathogens can be transmitted in many ways:

- Direct physical contact

- Inhaled air

- Indirect physical contact

Pathogen transmission

- Exchanging body fluids

- Faecal-oral route

- Vector organisms

Transmission Summary

• Disease can be transmitted by :– direct physical contact, – water, – food, – body fluids, – inhaled air – vector organisms.

Controlling transmissionBecause we know how pathogens are

transmitted we can interrupt it by the following;

- Antisepsis – inhibiting or destroying a microorganism by sterilising everything that could carry a pathogen or prevent them reaching somewhere.

Controlling transmissionQuarantine – isolating the person who is

infected or has been in contact with an infected person to prevent spreading of the disease.

The length of the quarantine is usually just over the length of time it usually takes for someone to display symptoms after being infected.

Individual responsibilityKnowing what we do about transmission of

pathogens there are a number of things that can be used to prevent it;

- Good hygiene – washing hands, brushing teeth, showering

- Care in sexual health – use of condoms to prevent sexually transmitted diseases

- Handling and storage of food – washing hands, keeping raw and cooked food separate and at the appropriate temperatures.

Community responsibilityClean water supply – our water is filtered and

chlorinated to prevent growth of microorganisms… is everyone as lucky?

Safe food webs – for example, milk pasteurisation (heating at 72o C to kill any microorganisms)

Waste disposal – keeping any refuse collected regularly and buried or incinerated.

Community responsibility

Control of vectors – Taking care to eradicate any animals which can carry diseases e.g.

Bubonic plague was caused by bacteria carried by fleas on rats so being in close proximity to rats carrying those fleas put you at high risk.

Malaria is caused by a protozoa carried by female mosquitoes in their saliva. How could you protect people from this animal vector?

Swine flu in Scotland – Data Handling Exercise – Collect worksheet

Epidemiology of infectious diseases

Epidemiology is the study of the characteristics of an infectious disease.

We would look at:

- The location of an initial outbreak- The pattern and speed of the spread- The geographical distribution

Patterns of distribution

Sporadic – occurs in scattered or isolated instances with no connection between them

Endemic – recurs as a regular number of cases in a particular area

Epidemic – affects an unusually high number of people in a particular area

Pandemic – occurs as a series of epidemics spreading across continents or the whole world

Methods of Controlling Disease

• Based on epidemiological studies control measures can be considered

• Control measures include – preventing transmission, – drug therapy, – immunisation – a combination of these.

Preventing Transmission

• It is important to put measures in place to stop the transmission of disease from person to person and region to region

• Millions of school days are lost each year by pupils because of transmissible disease.

Drug Therapy

• For people already infected with a transmissible disease then drug treatment is important to reduce spread

TB antibiotics

Immunisation• Immunisation is what

happens in your body after you have had a vaccination.

• The vaccine, which contains inactivated or weakened viruses or bacteria (or parts of them), stimulates your immune system so that it can recognise and protect you from future infection (i.e. you become immune to the infection).

QuestionsThe uptake of vaccine against measles and the number of reported cases of measles in Scotland over a ten year period is shown in the table below

Year Vaccine Uptake (%) Number of reported cases (all ages)

2002 93.0 395

2003 91.0 315

2004 90.0 396

2005 87.5 412

2006 83.0 530

2007 79.5 792

2008 86.0 482

2009 91.5 322

2010 95.0 112

1. Draw a line graph of this information – hint: you will need to create a graph with TWO Y axis, one for each set of information with the Year along the X axis.

2. Describe the trend in vaccine uptake between 2002 and 2009.

3. Use the data in the graph to justify the following statement: “As vaccine uptake increases the number of reported cases falls”.

4. Are there any results which contradict this statement

5. Calculate the percentage decrease in the number of reported cases of measles from 2002 to 2003.

Answers

1. Marks – two scales and labels, plotted and joined dots

2. Decreased from 2002 to 2007 then increased – bonus if use data to support this.

3. Vaccine uptake increases from 79.5% in 2007 to 95% in 2010, the number of cases falls from 792 in 2007 to 112 in 2010.Or converse of data for 2002 to 2007.

4. 2003.

5. 395-315=80/395 x 100 = 20.25 or 20%