Disease and Immunity Chapter 10 Pathogen A pathogen is a microorganism which causes disease Examples: Various types of bacteria, viruses, fungi, and parasites Types of Pathogens Bacteria: are tiny, singlecelled organisms, that get nutrients from their surroundings Viruses: are even smaller than bacteria. They are simply a genetic material (DNA or RNA) packaged inside of a protein coating. They need to use another cell’s structures to reproduce Fungi are eukaryotes, and their diseases are particularly dangerous to immunocompromised people Parasites: are also eukaryotes, usually larger than bacteria, can either be unicellular or multicellular. Immune System Immune system is a large network of organs, white blood cells, proteins (antibodies) that work together Immune system works together to protect you from foreign invaders like bacteria, virus, fungi and parasites which causes infection, illness and disease Difference between pathogen and antigen A pathogen is an agent that can cause diseases in the host An antigen is a molecule capable of inducing an immune response in the host Two types of transmissible diseases • Communicable disease : passed form person to person Examples: flu, hepatitis A • Non-communicable disease: cannot be passed from person to person Examples: cardiovascular diseases, diabetes, cancers Videos What are Pathogens? • https://youtu.be/WsZS4RCWpcE Immune System • https://youtu.be/Ky-gNIlejwM Endemic Vs Epidemic Vs Pandemic Endemic level of a disease is the amount that is usually present in a given community Epidemic is a drastic increase in the numbers of people infected with that disease, in that same community Pandemic is an epidemic that has spread to several countries or continents, affecting a large number of people Epidemics and pandemics in the past decade Ebola virus (2013 – 2016) Zika virus (2015 – 2016) Covid-19 virus (2019 – present) Time to do a brief research work on the above viruses. Brief history: Summer of 1976, a mysterious epidemic struck2 central African towns, Yambuku (Zaire) and Nzara (Sudan), killing many people Ebola virus (2013 – 16) Medical researchers suspected the deadly Marburg virus to be the culprit To their surprise found a new pathogen under the microscope, named as Ebola after the nearby Ebola river. Ebola virus Disease caused by Ebola virus is a severe type of haemorrhagic fever After contracting the virus from 2 to 20 days, symptoms are high temperature, aching, sore throat, resembles a typical flu, but quickly escalates to vomiting, diarrhoea Finally attacks the lymph nodes, kidneys and liver, causing them to lose their functions What causes death of Ebola victims? Mounting cell deaths, trigger an immune system overload, known a cytokine storm, damages blood vessels Causes both internal and external bleeding Excessive fluid loss and resulting complications can be fatal within 6 to 16 days of the first symptoms Proper care and rehydration therapy can significantly reduce mortality rates in patients Ebola can only exists in bodily fluids like saliva, blood, mucus, vomit or faeces Some factors limits Ebola virus’s contagiousness It has to transmitted from one infected person to another person’s body through passageways like, eyes, mouth, or nose – DIRECT CONTACT Once the outbreak has been contained, the virus does not exist in the human population until the next outbreak begins Though it is an ideal situation, but scientists feel this makes the study of the Ebola virus very difficult Countries where Ebola virus occurred are mainly due to poor infrastructure and sanitation – enabling the virus to spread Ebola virus – Conclusion Governments are spending to find an effective vaccine Poverty of these regions coupled with relatively low amount of overall cases means there is little incentive for drug companies to invest in research Only effective solution to Ebola outbreak remains, isolation, sanitation, information Zika Virus (2015 – 16) History : It was first isolated from the monkeys in 1947, in the Zika rainforest, Uganda, since then it did not bother the humans at all In 2015, Brazil, more than a million people were infected with the Zika virus Zika virus infection is carried by the mosquitoes Zika Virus 80% of the population have no symptoms at all Mild symptoms such as fever, rash, joint pain, red eyes, muscle pain , headache Why is Zika virus : of so much concern? Causes congenital abnormalities in the foetus of the pregnant women Microcephaly is the condition caused in foetus Microcephaly is an incomplete head and brain development – so they the new-born seems to have very small head, means mentally disabled, shorter life expectancy Zika virus - Precautions No protection Vaccines are in research stages Pregnant women to avoid traveling to destinations where Zika virus is spreading Knowledge and awareness of virus to be shared with pregnant women Covid -19 infection Caused by the SARS-CoV-2 Spreads in crowded places, closed spaces with poor ventilation, or prolonged contact with infected person In closed spaces, social distancing helps, open windows, wear a mask, limit the time spent in these settings Protection from Covid -19 infection Follow these 6 precautions: • Keep at least 1m distance from others • Wash your hands with soap • Cough or sneeze into your elbow • Wear a mask • Open a window • Get vaccinated when it is your turn How a pathogen is transmitted? Session 3 How a pathogen is transmitted? Two ways a pathogen can be transmitted Direct transmission Indirect transmission In direct contact, some pathogens pass from one person to another when there is a direct contact between an infected person and an uninfected one Direct transmission Such diseases are called as transmissible diseases ( contagious diseases) Example: Human immunodeficiency virus (HIV) causes AIDS, can be transmitted when an infected person’s blood comes into contact with another person’s blood Example: Athlete’s foot fungus It happens through: Indirect transmission • Breathing in droplets containing pathogens, ex: cold, Covid-19 virus • Touching a surface that someone with the pathogen has touched (fomites), ex: Cold, Covid-19 Virus • Eating food or drinking water that contains pathogens, ex: Salmonella (bacteria), larger the number of bacteria causes food poisoning • Contact with animals that are carrying pathogens, ex: malaria, zika, plague Always wash fruits and vegetables before you eat Precautions to be taken in order to eat safe Cooking destroys bacteria, so recently cooked food is generally safe Governments do check on food sellers to ensure that they are following good hygiene, their food is safe to eat Viruses transmitted in water Virus that causes polio and bacterium that causes cholera are transmitted in water Mode of transmission of the above virus/bacterium – when you either swim in this water or drink this water Types of disease transmission – Direct transmission Disease transmission Mode of transmission Diseases caused Direct transmission Spread through droplets Covid_19 Direct transmission Spread by skin Chicken pox Direct transmission Spread through blood or body fluids HIV Direct transmission Person to person Measles, HIV Types of disease transmission – Indirect transmission Disease transmission Modes of disease transmission Diseases caused Indirect transmission Airborne transmission Influenza, Indirect transmission Contaminated object (fomite) Covid-19, cold Indirect transmission Vector-borne transmission malaria Indirect transmission Transmission through food and water Cholera, diarrhoea Indirect transmission Transmission through animals rabies Indirect transmission Environmental factors Hookworm, Legionnaire’s disease Body Defences Session 4 and 5 Body defences Body has many natural defences such as skin, hairs (in the nose), mucus, WBC, to fight against the pathogens Purpose: To prevent the pathogens from getting to various parts of the body, where they could breed What if the pathogen manage to get through all of these defences? The pathogens are usually destroyed by WBC Some of these WBC take in digest pathogens, by phagocytosis B cells produce chemicals called antibodies that incapacitate or directly kill the pathogens • The first line of defence against pathogens is called physical barriers Body defences – Physical barriers • The skin – secretions such as sweat • Cornea of the eyes – secretes tears • Membranes lining the digestive, respiratory systems - mucus First line of defence Skin • Skin prevents pathogens from entering the body. • If the skin is broken, a blood clot forms to seal the wound and stop pathogens from getting in First line of defence – hairs in the nose • It helps to filter out particles from the air, which could contain pathogens • Smell or taste food which is bad, don’t want to eat as it would make us sick First line of defence – mucus membrane (chemical barrier) Mucus in airways traps bacteria They are then swept up to the back of the throat and swallowed, rather than being allowed to get into the lungs First line of defence – stomach containing hydrochloric acid (chemical barrier) Stomach contains HCl, which kills a lot of bacteria in our food Second line of defence – WBC(white blood cells) WBC travel through the blood stream, into the tissues, searching for and attacking microorganisms and other pathogens One type of WBC are phagocytes – ingest the pathogens (phagocytosis) Antibodies are proteins produced by a type of WBC, called B cells Antibodies tightly binds to the antigen of an invader, directly neutralizes it Each antibody is specific to a given antigen Certain factors are important in controlling the spread of the disease A clean water supply Hygienic food preparation Good personal hygiene Sewage treatment 1) A clean water supply Clean water supply is one of the most basic health need Water supply is treated with chlorine to kill all the microorganisms, before being supplied to homes Another source of clean water supply is deep well or tap (communal source) When water has not been made safe to drink? It becomes a source for pathogens Can be very dangerous, such as bacterium which causes cholera or virus that causes polio 2) Food hygiene Food prepared with good hygiene will or may not cause any sickness Food poisoning is mainly caused by bacteria Ways to follow good food hygiene: (A) Always wash your hands before touching/eating food. Never cough or sneeze over food. People working in the food and beverage industry often wear uniforms, or aprons, hairnets, gloves for safe handling of food (B) Keep animals away from food. For example, houseflies have harmful bacteria on their feet (as they may have been walking on rubbish, faeces or dead animals). These houseflies in turn sit on the food and transmit the bacteria. Rats often carry pathogens. Ways to follow good food hygiene (C) Avoid keeping food at room temperature for long hours. Refrigerating food slows down the bacterial growth. Cooking at high temperature too will kill most of the bacteria. While reheating food, make sure the food is heated up nicely. Below 1 degree Celsius – most growing bacteria does not reproduce From 10 degree Celsius to 48 degree Celsius – most growing bacteria grow well Above 65 degree Celsius – most growing bacteria are killed 120 degree Celsius – bacterial spores are even killed Ways to follow good food hygiene (D) Raw meat must always be stored separately from other foods. Raw meat contains bacteria, which can be killed while cooking. Raw vegetables and salads have to be washed in clean water before eating, unless they have been packaged, where they do not contain bacteria 3) Good personal hygiene Keeping body clean reduces risk of being infected or passing on transmissible diseases Oil (skin makes an oil to keep the skin supple, waterproof), dirt ( from things we have touched), and sweat (from sweat glands) become the breeding grounds for bacteria Washing regularly with soap prevents this from happening Brushing twice a day helps us to fight bad breadth and tooth decay Mouthwash keeps the harmful bacteria under control Rubbish such as waste food, paper packaging materials, cardboard, bottles, cans, newspapers, magazines, plastic bags are all thrown away Waste accumulates in places where people live and work. 4) Waste Disposal Animals such as rats, flies, stray dogs feed on the waste Bacteria breed in the waste food Waste is further taken to landfill sites Rubbish is also decomposed by bacteria. This produces methane gas, which could cause explosions, if it builds up. Placing pipes in the rubbish can allow methane gas to escape to the air. Sewage is a waste liquid that has come from houses, industry and other parts of villages, towns and cities Mainly contains water, includes urine, faeces, toilet paper, detergents, oil and many other chemicals 5) Sewage treatment Sewage has to be treated before being discharged into sea or rivers. As untreated sewage contains pathogens People who come in contact with raw sewage, can fall ill Poliomyelitis and cholera are two of the serious diseases transmitted through water polluted with untreated sewage Cholera Transmissible disease caused by a bacterium called vibrio cholerae bacteria Dr John Snow discovered the source of cholera outbreak in London He traced it to the poor sewer wastewater management in the city His discovery allowed for the improvement of water sanitation and waste management Cholera Most common cause of bacterial gastroenteritis in the developing world Mode of transmission: living in areas of poor sanitation which leads to contaminated food and water This Photo by Unknown Author is licensed under CC BY-ND Link to YouTube video https://youtu.be/kXf8MkpALrc What happens if one contracts the infection? • Cholera bacteria first needs to make its way past the acidic environment of the stomach, into the small intestine • The wall of the small intestine has epithelial cells • Once the bacteria is near the epithelial cells, it will start to produce the cholera toxin, which enters the epithelial cell • It causes a whole range of biochemical reactions • It causes secretion of whole bunch of things from within the cell into the lumen What happens in the lumen? • Lumen is a space through which food and water passes through the small intestine • Mostly ions get secreted out such as sodium ions, potassium ions, chloride ion, bicarbonate ion, water is also going to leave. • As a result the cells are squeezed, not only they are absorbing water but all contents are removed from the cells – that is the source for dehydration and cause for diarrhoea Cholera bacteria produces toxin The toxin attaches to the walls of the small intestine Toxin stimulates the release of chloride ions Cholera infection Chloride ions are secreted into the small intestine Chloride ions lower the water potential of the intestinal lumen or create a water potential gradient between the intestinal lumen and the surrounding cells Water moves into the intestine by osmosis Salts (in the form of chloride ions) are lost from the blood Diarrhoea/ dehydration can result Cure for Cholera Drink fluids, IV fluid, antibiotics Eat and drink clean food and water Vaccination is available An Immune Response is Recognizing Recognizing a potentially harmful foreign antigen Activating and mobilizing Activating and mobilizing forces to defend against it Controlling and ending Controlling and ending the attack Antibodies • Lymphocytes produce antibodies • An antibody is a protein molecule with a particular shape • This shape is going to be complimentary to the shape of another molecule, called an antigen • Antigens are found on the outside of the pathogen Antigens • Each pathogen has its own antigens, which have specific shapes Antibody must have a complementary shape to the antigen • In order to destroy a particular pathogen, antibody molecules must be made, which are perfect complementary shape to the antigens on the pathogens • Diagram to show each lymphocyte produces only one type of antibody Mode of action between antibodies and antigens In some cases, antibody molecules bind with the antigen – which directly kills the pathogen In other cases, antibodies clump the pathogens called agglutination – wherein the pathogen cells cannot move very easily • Sometimes chemicals are released to signal to phagocytes that there are cells present which needs to be destroyed Continued • Pathogen enters the body, meets a large number of lymphocytes • One of the lymphocytes might recognise the pathogen, as its antibody can destroy • This lymphocyte will start to divide by mitosis, making more copies of it Continued The lymphocytes then secrete their antibody, destroying the pathogen This takes time During this time, the pathogen can make you ill. However, the lymphocytes, antibodies, and phagocytes always manage to kill the pathogen, make you get better Lymphocytes Are very important part of your immune system The way in which they respond to pathogens, by producing antibodies, is called immune response • Memory cells are produced during a specific immune response. Memory Cells When an individual’s specific immune system responds to a pathogen, memory cells are produced. They are only produced when the specific immune system is activated – that is the response involving lymphocytes and antibody production Memory cells • Memory cells help protect against future infections by the same pathogen The memory cells can stay in the blood for many years, and if the same pathogen infects again with the same antigen, the memory cells can quickly produce antibodies. Therefore the body’s immune response is much quicker second time around in the secondary response to an antigen. This is why you are unlikely to get a disease like chicken pox again after you had it once. The reason being the body has memory cells and will quickly respond second time around. Memory cells play an important role in vaccination. Active immunity • This is when the body is activated and produces the antibodies needed to fight an infection • Slow acting • Provides long-lasting protection • The primary response when a microorganism enters the body is described as natural active immunity • Vaccines provide artificial active immunity Passive immunity This is when ready-made antibodies, from another source, are introduced to the body Fast-acting Only lasts a short period of time Breastfeeding provides a baby with natural passive immunity Anti-venom provides artificial passive immunity after a poisonous bite Controlling disease by vaccination Vaccination aims to create memory cells. Vaccination basically injects an inactive form of a pathogen into the body. This further activates an immune response and antibody production, memory cells are made This protects the individual in case the real pathogen enters the blood again Vaccinations use inactive or dead pathogens Obviously we do not want to infect the individual using a vaccination, otherwise they could get the disease So instead we give a dead, weakened or inactivated pathogen, which still has the same antigens as the normal pathogen( needed to activate the immune response) but is harmless Vaccines enable the immune response to occur quickly • Data shows that vaccinations can allow the body to rapidly eliminate a live infection for the first time within seven days, with the peak of the immune response occurring within the first three days Herd Immunity • Mass vaccination contributes to herd immunity. When the majority of a population is vaccinated against a pathogen, it breaks the pathogen’s chain of infection, hence vaccination prevents the spread of disease. This means that the virus essentially disappears because it is unable to pass from person to person. Members of population, such as infants, who have not received vaccinations yet, are protected against the pathogen. Vaccinations are often given early in life • We vaccinate against diseases which a person has not encountered before(and therefore the person won’t have memory cells) • It is important to give vaccination early in life before the person gets the disease.
