Cf E Higher Human Biology Section 2 of

Cf. E Higher Human Biology Section 2 of Unit 4 Infectious Diseases & Immunity

Learning Objective 2. 1 Infectious Diseases and Immunity 2. 2 Infectious Diseases and Immunity – Transmission

Classification of microbes Giardia Algae Fungi Trichophyton. ATHLETES FOOT Bacteria E. coli Protozoa Viruses Cold /flu

Pathogens and disease An infectious disease is a disease resulting from infection of a host organism by a pathogen, a disease-causing organism. There are several different types of pathogen including bacteria, fungi, viruses and parasites. Infectious disease is a major cause of death worldwide. It is estimated that 14. 7 million people died in 2002 due to infectious diseases.

Trichophyton-ATHLETES FOOT Cause- fungal growth on surface of skin Symptoms-Dry flaking skin on the soles of the feet. Unpleasant foot odour. Small itchy bubbles or blisters on the soles of the feet. Transmission- Athlete's foot is mildly contagious. It can be spread through direct contact with the infection and by skin particles left on towels, shoes, floors of shower cubicles and changing rooms, and around pools. Treatment- Most cases of athlete's foot can be cured with over-the-counter antifungal products and basic good hygiene.

E. coli Cause- most strains are harmless and are found in the intestines of most animals. The strain E. coli 0157 is harmful. Symptoms- cramping vomiting, diarrhoea, fever dehydration Transmission- eating undercooked meat or consumes unpasteurised milk or cheese. Having contact with infected animals, such as on farms and at children's petting zoos. Contact with other people who have the illness, through inadequate hand-washing after using the toilet and before handling or eating food. Eating unwashed vegetables which have come into contact with manure from infected cattle. Drinking or swimming in infected water. Treatment- Drink plenty of fluids

Influenza Cause- viral infection Symptoms- It usually causes aching muscles and joints, headaches fevers and coughs. Can lead to pneumonia, nerve and brain damage and even death Transmission- person to person through the air Treatment- rest sleep plenty of fluids antiviral drugs, vaccination

How easily can a disease be transmitted by hand to hand contact? Activity

Transmission l The main ways a disease can spread from person to person are: l 1. Air - when someone coughs or sneezes, a spray of tiny watery droplets enters the air. These may contain microbes. l If someone else breathes in the droplets they may become infected with the microbes and get a disease l Colds, flu, measles, chickenpox and TB are all spread in this way

How virus attacks body l

Transmission l 2. Touch – some diseases are passed on by touching an infected person l Athlete’s foot can be spread by touch or indirectly, by treading barefoot on a wet floor where an infected person has recently trodden l MRSA can be spread from person to person by touch or by contact with sheets, clothing or equipment

Transmission

Transmission l 3. Water – in overcrowded conditions, people’s sewage can get into the drinking water l Cholera can spread in this way l Why do you think cholera often occurs in areas hit by wars or natural disasters?

Transmission l 4. Food – food poisoning is caused by bacteria in food l Animals learn to avoid eating certain foods that make them ill l Humans have learned to cook – which should thoroughly kill bacteria

Transmission l 5. Vectors – Some microbes are carried by animals l E. g. mosquitoes carry the microbe that cause malaria & yellow fever

l E. g. mosquitoes carry the microbe that cause malaria & yellow fever

l

Transmission l Direct physical contact l Water l Food l Body fluids l Inhaled air l Vector organisms.

Vector l Vectors organisms provide a pathway for a pathogen to be transmitted between animals and humans or other animals. l Some vector organisms provide this transport by the means of blood-sucking. l Malaria caused by the protozoa Plasmodium spread by mosquitoes l Dengue Fever (DF) is a virus-caused disease also spread by mosquitoes.

Control l Quarantine l Antisepsis (prevent disease infection through inhibition or arresting the areas of growth of the infection). l Individual responsibility (good hygiene, care in sexual health and appropriate storage/handling of food), l Community responsibility (quality water supply, safe food webs and appropriate waste disposal systems) l Control of vectors

Success Criteria l Due to its role in maintaining health and combating infectious diseases on a global level, the immune system is at the centre of much of the research in public health. l Infectious diseases are caused by pathogens such as viruses, bacteria, fungi, protozoa and multicellular parasites. l Infectious diseases are transmitted by direct physical contact, water, food, body fluids, inhaled air or vector organisms. l The transmission of infectious disease can be controlled by quarantine, antisepsis, individual responsibility (good hygiene, care in sexual health and appropriate storage/handling of food), community responsibility (quality water supply, safe food webs and appropriate waste disposal systems) and the control of vectors.

Learning Objective 2. 3 Infectious Diseases and Immunity – Epidemiology

Epidemiologists l the outbreak and pattern of infectious diseases to determine the factors which affect the spread of infectious disease

Outbreaks of disease can occur on different levels: l sporadic – (occasional occurrence) the disease occurring occasionally, singly or in scattered instances. l endemic – (regular cases occurring in an area) it is continually present in a population but at a low level (for example the common cold). l epidemic – (unusually high number of cases in an area )it ) has suddenly increased above the normal endemic level and infects many people. l pandemic – (a global epidemic ) it is epidemic over a very wide area (usually a continent or the world).

Depending on epidemiological studies, measures are considered to control the spread of diseases. lpreventing transmission ldrug therapy limmunisation

Success Criteria l Epidemiologists study the outbreak and pattern of infectious diseases to determine the factors which affect the spread of infectious disease. l The spread of infectious diseases are classified as: sporadic (occasional occurrence), endemic (regular cases occurring in an area), epidemic (unusually high number of cases in an area) or pandemic (a global epidemic). l Based on epidemiological studies control measures can be considered that include preventing transmission, drug therapy, immunisation or a combination of these.

Learning Objective 2. 4 Infectious Diseases and Immunity – Active Immunisation and Vaccination

Types of Immunity - note Active immunity- antibodies made by individual in two ways l. Natural Acquired Active – Antibodies made by individual in response to antigen l. Artificially Acquired - In response to vaccine. Two Kinds of Passive immunity- Antibodies given to individual l. Natural - Ingested with milk shortly after birth l. Acquired – injection of antibodies to combat a disease e. g. rabies

Active immunity Antigens usually mixed with an adjuvant to form the active vaccine and enhance the immune response Vaccines include linactivated pathogen toxins ldead pathogens lparts of pathogens lweakened pathogens.

Antibody responses Memory Cells – lymphocytes specific to antigen from first exposure to it.

l The immune system can also be activated artificially by the use of vaccines

Who is Edward Jenner? l Edward Jenner

Smallpox

Edward Jenner & the Small Pox Vaccine l Use this website: l http: //www. jenner. ac. uk/edwardjenner to find out about how Edward Jenner developed the Small Pox Vaccine. l Write a short note including: l When he did this work l How he linked cowpox and smallpox l How he tested the vaccine l When smallpox was eradicated

The Independent - Thursday 22 May 2014 l The General Assembly of the WHO will take a vote on Friday (23 rd May) on whether to eradicate the variola virus completely and forever by ordering the incineration of stockpiles in Russia and the United States, which are kept under an agreement signed in 1983 when Ronald Reagan was US President and the Soviet Union was still a country. l http: //www. independent. co. uk/news/science/h ealth-experts-to-vote-on-whether-to-destroy-the -last-few-samples-of-smallpox-9412451. html

Any further news? Google smallpox to find out!

Success Criteria l Antigens from infectious pathogens, usually mixed with an adjuvant to form the active vaccine and enhance the immune response, include inactivated pathogen toxins, dead pathogens, parts of pathogens and weakened pathogens. l These agents induce a primary immune response and immunological memory in the individual but not disease symptoms.

Learning Objective 2. 5 Vaccine Clinical Trials

Few people Larger number Double blind procedure, placebo Long term effects

Success Criteria l Vaccines are subjected to clinical trials in the same way as other pharmaceutical medicines to establish their safety and efficacy before being licensed for use. l Clinical trials use randomised, double-blind, placebo-controlled protocols. Subjects are split into groups in a randomised way in which neither the subjects nor the researchers know which group they are in to eliminate bias. l One group of subjects receives the vaccine, while the second group receives a placebo control to ensure valid comparisons.

Learning Objective 2. 6 Herd Immunity 2. 7 Public Health Medicine

The herd immunity threshold depends on: 1. The disease. 2. The efficacy (effectiveness) of the vaccine. 3. The contact parameters for the population.

Pros Difficulties protects vulnerable The developing worldand the non-vaccinated vaccination is not possible due to malnutrition and poverty reducing the spread of The developed worlddiseases vaccines are rejected by a percentage of the population.

The MMR controversy In 1998, a scientific paper was published in the medical journal The Lancet, speculating that the MMR vaccine could cause autism. The authors thought that the MMR vaccine could damage the bowel, allowing toxins that are normally destroyed in digestion to move into the blood. If these toxins travelled to the brain they might cause autism. The authors did not prove that this was the case but still recommended that doctors stop administering the MMR vaccine until more research was done.

The media’s role in the MMR controversy Many studies have concluded that the MMR vaccine is safe and only a few studies claim that it isn’t. However, this was not reflected by the media coverage. The majority of coverage centred on the possibility of a link between the MMR vaccine and autism, while the government insisted that the vaccine was safe. This mixed message caused confusion among the general public, leading to a drop in the number of children being given the combined vaccine. Should scientists be more careful about how they present their research or should the media be responsible for how they present controversial topics to society?

Evaluating scientific papers

Success Criteria l If a large percentage of a population are immunised, nonimmune individuals are protected as there is a lower probability that they will come into contact with infected individuals. l This herd immunity is important in reducing the spread of diseases and in protecting vulnerable and the non-vaccinated l The herd immunity threshold depends on the disease, the efficacy of the vaccine and the contact parameters for the population. l In most countries, policy in public health medicine is to establish herd immunity to a number of diseases. l Difficulties can arise when widespread vaccination is not possible due to malnutrition and poverty (the developing world), or when vaccines are rejected by a percentage of the population (the developed world).

Learning Objective 2. 8 Evasion of specific immune responses by pathogens 2. 9 Antigenic Variation

l Many pathogens like viruses, bacteria and protozoa can evolve mechanisms that evade the specific immune system of the human body and can affect vaccination strategies globally. l Antigenic variation is a process by which a pathogen is able to change its surface proteins so that it can evade the host immune responses.

l The antigenic profile will change as the pathogen passes through the host population or in the original infected host. l Antigenic variation is particularly important for pathogens as it allows them to: Ø target hosts which are long-lived or susceptible to the pathogen Ø infect a single host on more than one occasion Ø transmit the disease easily This drift results in small antigenic changes in the pathogen population and will reduce the efficacy of B and T cell memory during the host immune response.

Success Criteria l Many pathogens have evolved mechanisms that evade the specific immune system which has consequences for vaccination strategies. l Some pathogens can change their antigens avoiding the effect of immunological memory. l Antigenic variation occurs in diseases like malaria and trypanosomiasis and is one of the reasons why they are still so common in many parts of the world. l Antigenic variation also occurs in the influenza virus explaining why it remains a major public health problem and why at risk individuals require to be vaccinated every year.

Learning Objective 2. 10 Direct attack on the immune system

HIV attacks lymphocytes and is the major cause of acquired immunodeficiency in adults

TB l Tuberculosis (TB) survives within phagocytes and avoids immune detection.

Success Criteria l The absence or failure of some component of the immune system results in increased susceptibility to infection. l HIV attacks lymphocytes and is the major cause of acquired immunodeficiency in adults. l Tuberculosis (TB) survives within phagocytes and avoids immune detection.