Bellwork: How has humanity s understanding of how disease s spread changed over the course of history

Transcription

1 Bellwork: How has humanity s understanding of how disease s spread changed over the course of history

2 Chapter 35 - immune system and disease Section Infectious disease

3 What causes an infectious disease? During the mid 19th Century, Louis Pasteur and Robert Koch established a scientific explanation for infectious diseases They concluded that microorganisms cause physiological changes that disrupt normal body functions Referred to as germ theory (microorganisms were referred to germs) Nowadays germ has no scientific significance! Instead - there are a variety of agents of disease Viruses Bacteria Fungi Protists Parasites All (apart from parasites) are called pathogen

4 Pathogens defined...

5 What is a postulate? Definition: A thing suggested or assumed as true as the basis for reasoning, discussion, or belief. Koch developed a series of specific rules for identifying the microorganism that caused a disease The pathogen must always be found in the body of a sick organism and should not be found in a healthy one The pathogen must be isolated and grown in the laboratory in pure culture When the cultured pathogens are introduced into a healthy host, they should cause the same disease that infected the original host The injected pathogen must be isolated from the second host. It should be identical to the original pathogen Koch received a nobel prize in 1905 for his work

6 What is the difference between a symbiont and a pathogen? We have a number of microorganisms in our body that are harmless, or can actually be beneficial - symbionts Example - yeast and bacteria in your mouth and throat, bacteria in your large intestine They all obtain nutrients, grow and reproduce without causing trouble Pathogens cause problems in a number of different ways Some viruses and bacteria directly destroy the cells of their hosts Other bacteria and single cell parasites release poisons that kill the hosts cells, or interfere with their normal functions Parasitic worms may block blood flow through blood vessels or organs, take up the hosts nutrients, or disrupt other body functions.

7 How are diseases spread? Diseases can be spread through coughing, sneezing, physical contact or exchange of bodily fluids Pathogens are also often spread to surfaces such as doorknobs, lying in wait to infect other unsuspecting people Can be controlled through frequent hand washing Pathogens transferred via bodily fluid can be transferred through sex, shared syringes amongst drug users, or blood contact Contaminated food and water can also spread diseases Many diseases are spread through water contaminated with feces from infected people or other animals Diarrhea is aver common symptom - exasperates the problem in areas of poor sanitations Contaminated water can be consumed, or may be carried on fruits and vegetables - always wash in clean water! Meat and seafood can also contain bacteria - also cook properly!

8 What is zoonosis? A zoonosis is any disease that can be transmitted from an animal to a human Mad cow disease, SARS, west nile disease, Ebola, Lyme disease, Bird Flu are all zoonoses Transmission can occur in a variety of ways A vector, is a carrier who transports the pathogen but does not get sick themselves A bite from an infected animal, or eating the meat of an infected animal may also transfer the disease

9 Key points What types of organisms can cause a disease? How can pathogens cause a disease in their hosts? How can infectious diseases be spread? What is a vector? How does it contribute to the spread of a disease? Why is it a beneficial adaptation for a pathogen to make a host very sick, but not kill the host?

10 Defense against infection Section 35.2

11 How does your body protect itself from infection? The body has a series of nonspecific defenses - physical and chemical barriers, which act against a wide range of pathogens Skin acts as the first line of defense, but does not cover the entire body Saliva, mucus and tears all contain an enzyme - lysozyme, which breaks down bacterial cell walls Mucus will trap pathogens before it is expelled. Stomach secretions also destroy pathogens The second line of defense kicks in if pathogens make it into the body - for example through a cut Inflammatory response, interferons and fever

12 Why do cuts go red and get inflamed? Inflammatory response is the result of mast cells releasing chemicals called histamines Histamines increase the flow of blood and fluids to affected area Swelling caused by excess fluid White blood cells move from blood vessels into infected tissues Phagocytes engulf and destroy bacteria All this activity can cause an increase in temperature

13 Why do humans develop fevers? The immune system can release chemicals that increase the body temperature Increased body temperatures can slow down or stop the growth of some pathogens Higher body temperatures can also speed up several parts of the immune response Interferons are proteins that interfere with viral growth Can be produced by host cells when infected

14 What does your immune system do? The role of the immune system is to distinguish between self and other, and they inactivate or kill any foreign substance or cell that enters the body Specific defenses can respond to specific pathogens Chemical markers acts like a secret passwords, allowing the body to identify everything that belongs to it. Chemical markers are unique to an individual The body recognises invaders, and signals the attack using cellular and chemical weapons Once an invader has been attacked, your immune system will remember it, enabling a rapid and more effective response if encountered again - immune response

15 What is the difference between an antigen and an antibody Specific immune responses are triggered by antigens An antigen is any foreign substance that can stimulate an immune response Located on the outer surface of bacteria, viruses or parasites Immune system responds by either attacking invaders or producing proteins called antibodies Antibodies tag antigens for destruction Can be attached to immune cells, or free float in plasma The body makes up to 10 billion antigens

16 What do lymphocytes do? Lymphocytes are the main working cells of the immune response Two types - B lymphocytes and T lymphocytes B cells are produced and mature in red bone marrow T cells are produced in the bone marrow, but mature in thymus - an endocrine gland Each B and T cell is capable of recognizing one specific antigen Travel to lymph nodes and spleen, where they encounter antigens B cells have embedded antibodies, and discover antigens in body fluids T cells must be presented with antigens that have already been discovered

17 What are the body s specific defenses against pathogens? Humoral immunity is depends on the actions of antibodies that circulate in blood and lymph Activated when antibodies embedded on a few existing B cells bind to antibodies on the surface of an invading pathogen When a B cell binds to antigen, T cells stimulate B cells to grow and divide rapidly Two types of B cells are produced Plasma Cells - produce and release antibodies that are carried through the bloodstream - bind to antigens, and act like signal flags Only temporary, die after infection has gone Memory cells - remain alive for a long time, allow body to respond rapidly by producing new plasma cells if specific antigen encountered again Explains how vaccinations and immunity work..

18 Cell mediated immunity Depends on macrophages and several types of T cells Defends against viruses, fungi and single celled pathogens that work inside specific cells When a cell is infected, or when a macrophage consumes a pathogen, a small amount of the antigen is displayed on outer surface Acts as a signal to helper T cells, which when activated divide into more T cells that activate B cells, cytotoxic T cells and memory T cells Cytotoxic T cells hunt down and kill body cells infected with a particular antigen by puncturing membrane or initiating apoptosis Memory T cells ensure swift future response to same antigen Suppressor T cells prevent immune response getting out of control

19 Why can cytotoxic T cells cause problems? Organ transplants Would be recognized as an invader and signalled for destruction by the immune system Known as rejection Doctors search for organ donors whose cell markers are nearly identical to that of the recipient Recipient will also need to take drugs, often for the rest of their lives, to suppers the cell mediated immune response

20 Humoral immunity and cell mediated immunity compared

21 Key points What are the body's nonspecific responses against pathogens? How does the immune system identify a pathogen? How are the roles of B and T cells different? How are their roles similar? What are the two main pathways of specific immune repsonse?

22 Bellwork: How do vaccinations work?

23 Fighting infectious disease Section 35.3

24 How does a vaccine work? The injection of a weakened form of a pathogen, or a similar but less dangerous pathogen has lead to immunity for specific diseases Comes from Edward Jenner s work in smallpox He noted that people who contracted cowpox did not go on to develop smallpox He tested his theory on a young boy (James phillips) Injected with cowpox, and then smallpox. james was fine

25 So how do vaccinations actually work? A vaccination stimulate the immune system with an antigen. Memory B cells and memory T cells are produced that quicken and strengthen the body's response to a repeated infection Referred to as active immunity Can be the result of natural of deliberate exposure Passive immunity is the result of externally produced antibodies being released into a person s blood Only lasts a short time Can be useful - for example for fetus and newborn babies Effective way of treating rabies virus

26 Public health and medication In 1900, more than 30% of all deaths in america were caused by infectious disease. By 2005, less than 5% of all deaths were due to infectious disease - what caused this change? Public health measures were introduced Monitoring and regulating food and water supplies Promoting vaccination Educating and promoting behaviors that avoid infection Introduction of new medications Antibiotics which kill bacteria were first discovered by Alexander Flemming in 1928 He noticed that a type of mold inhibited bacterial growth - penicillin Do not work on viruses, but antiviral drugs inhibit the ability of viruses to invade cells and multiply

27 New and Re-Emerging diseases By 1980, medicine was thought to have conquered infectious diseases Vaccinations and public health measures had wiped out polio in the US and smallpox globally Antibiotics controlled bacterial diseases Epidemics were thought to be a thing of the past However, in recent years there have been a number of new diseases appearing AIDS, SARS, Ebola, Bird Flu, and old diseases are reemerging - why? Merging of human and animal habitats Trade of exotic animals Misuse of medication Tuberculosis and malaria are developing resistance to a wide variety of antibiotics People are failing to follo vaccination recommendations, which for some diseases such as measles is thought to relate to them making a comeback.

28 Key points How do vaccinations and externally produced antibodies help the immune system fight disease? What is the difference between active and passive immunity? Why are public health measures important? Why does a doctor need to know if a disease is caused by a virus or by a bacterium? Why are new and re-emerging diseases spreading? Has the ease and accessibility of global travel affected the spread of emerging diseases?

29 Immune system disorders Section 35.4

30 Why do some people suffer from allergies? Because their immune system goes into overdrive When a person suffers from allergies, allergens (such as pollen) enter the body, and trigger an inflammatory response Mast cells release histamines If in respiratory system, mucus production is increased, and the person sneezes. Antihistamines counteract the effects of histamines

31 What is Asthma? A chronic disease in which air passages narrow, causing wheezing, coughing and difficulty breathing Can be related to hereditary and environmental factors Asthma attacks can be triggered by respiratory infections, exercise, stress, medication, pollen, dust, tobacco smoke, pollution, mold and pet dander (dead skin) Can be serious and lead to permanent damage and destruction of lung tissue Inhaled medications can relax smooth muscles around the airways and relieve asthma symptoms

32 What is an autoimmune disease? This is when the immune system fails to recognise self and attacks cells that belong to it s body as though they were pathogens Type I diabetes, rheumatoid arthritis and lupus are all examples In type 1 diabetes antibodies attack insulin producing cells in the pancreas In rheumatoid arthritis, antibodies attack tissues around joints In lupus, antibodies attack organs and tissues causing chronic inflammation Some can be treated with medications that alleviate symptoms Example type 1 diabetes and insulin Others are treated with medication that suppress ordinary immune system, although these need to be used carefully!

33 What is AIDS? In the 1970s doctors began to recognise that people were developing diseases that are usually prevented by a healthy immune system (rare types of skin cancer, pneumonia, fungal infections in mouth and feet - all opportunistic diseases The conclusion was that these people had weakened immune system All linked to a new disorder (auto-immune deficiency syndrome - AIDS) :ayer research showed that this syndrome was in actual fact an infectious disease caused by a pathogen new to science. The cause of AIDS was shown to be the human immunodeficiency virus in 1983

34 Why is HIV deadly? HIV can hide from defenses of the immune system HIV attacks key cells within the immune system, leaving the body with inadequate protection against other pathogens HIV is a retrovirus, so it carries the genetic material in RNA rather than DNA Virus binds to receptor molecules, and inserts content into cell

35 What does the HIV virus actually do? How is it transmitted? It attacks helper T cells, which cripples the ability of the immune system to fight both HIV and other pathogens The fewer T cells, the more advanced the disease, and the more susceptible a person is to other diseases A person is diagnosed with AIDS when their T cell count is less than 1/6th the normal level Although deadly HIV is hard to transmit - only happens through contact with infected blood, semen, vaginal secretions, or breast milk Sexual intercouse, sharing needes, contact with infected blood or blood products or from mother to child through pregnancy, birth or breast feeding are the main ways that it is transmitted

36 How to prevent HIV infection? Is there a cure? Abstinence from sexual activity, and not injecting yourself with drugs People who have sex with drug abusers are at the highest risk Before 1985, HIV was inadvertently transmitted to people through blood transfusions - nowadays all blood is screened for HIV antibodies, and potentially infected people are discouraged from donating blood Currently there is no cure, but drugs make it possible to live with an HIV infection for years Fighting the virus relies on a combination of very expensive drugs, that fight the virus in several ways Interfere with the enzymes HIV uses to insert RNA into cell, converting RNA to DNA, and integrating new DNA into host cell Drugs are not available in large parts of the world Despite drugs used to try and control the disease, it remains a highly infectious and dangerous disease

37 Key points What happens during an allergy attack? What is an autoimmune disease? What can cause asthma? What virus causes AIDS? How is it spread? Why does a person with HIV find it hard to fight off other infections?