BIO101 Infection and Disease Lecture 10 PDF

Infection and Disease BIO101 LECTURE 10  What is infection? Infection is the invasion of a host organism’s bodily tissues by pathogens or infectious agents ,multiplication of pathogens and the reaction of host tissue against them.  Chain of in...

Infection and Disease BIO101 LECTURE 10  What is infection? Infection is the invasion of a host organism’s bodily tissues by pathogens or infectious agents ,multiplication of pathogens and the reaction of host tissue against them.  Chain of infection  Chain of infection is a set of 6 intertwined links that allow for communicable diseases to spread.  Each step of the chain is required to effectively transmit infectious illness.  Breaking any one of the 6 links can slow the spread of infectious disease. Pathogens ▪ A pathogen is a living thing that causes disease. ▪ Pathogenicity refers to the ability of a pathogenic agent to cause disease.  Reservoir It refers to any human being, animal, plant, soil, or inanimate matter in which a parasite lives, multiplies, and depends for its survival. a. Human cases and carriers: The Commonest source of infection is man. i. Healthy carrier: harbors the pathogen but never suffered from the disease caused by a particular pathogen. ii. Convalescent carrier: one who has recovered from the disease but continues to harbor the pathogen in his body.  Reservoir iii. Temporary carrier: this carrier state lasts for about 6 months. iv. Chronic carrier: harbors the pathogen for several years and sometimes for the rest of one’s life. v. Paradoxical carrier: A person who acquires the pathogen from another carrier. vi. Contact carrier: one who acquires the pathogen from a patient.  Reservoir b. Animals Infectious diseases transmitted from animals to man are called zoonoses. Zoonotic diseases may be: Bacterial – bovine tuberculosis Viral- rabies from dogs Protozoal – Toxoplasmosis from cats Helminthic – Taeniasis from cattle Fungal- dermatophytes from dogs  Reservoir c. Insects Diseases transmitted by insects are called arthropod-borne diseases. Insects transmitting diseases are called vectors. Mechanical vectors: carry the organisms on their wings, legs, and body. Eg transmission of typhoid bacilli to man through food by domestic flies. Biological vectors: the pathogen multiplies in the body of the vector. E.g. female anopheles mosquito in malarial parasite. Extrinsic incubation period: after the entry of the pathogen in the vector the time required for the vector to become infective. d. Soil and Water Some pathogens survive in the soil for long periods. E.g. spores of tetanus and gas gangrene bacilli, the fungus causing histoplasmosis, and parasites such as roundworm and hookworm. Contamination of water with Vibrio cholera and hepatitis virus act as the source of infection.  Reservoir e. Food Contaminated food acts as a source of infection in the case of food poisoning, gastroenteritis, diarrhea, and dysentery.  Modes Of Transmission i. Contact a. Direct contact – directly through physical contact. STDs such as syphilis, gonorrhea, herpes simplex type 2, and AIDS. b. Indirect contact- indirectly acquired through fomites. ii. Airborne transmission: a. Droplets of respiratory infection are spread by inhalation. b. Droplet nuclei (1-10 micron diameter) remain airborne as aerosols act as a source of infection. iii. Ingestion Intestinal infections like cholera, dysentery, food poisoning, etc are acquired by ingestion of food or drink contaminated by pathogens.  Modes of Transmission iv. Inoculation Direct inoculation in the tissues e.g. rabies virus inoculation through dog bite or spores of Cl. tetani leading to tetanus. v. Transplacental Transmission of the pathogen from mother to fetus via placenta. Eg rubella virus, toxoplasma, CMV. Also known as vertical transmission. vi. Iatrogenic infection Infections like AIDS and Hepatitis B are transmitted during lab and surgical procedures such as lumbar puncture, blood transfusion, dialysis, and surgery. What if you can fight against disease- causing organisms ? Immune system Organs and tissues important to the proper functioning of the immune system include the thymus and bone marrow, lymph nodes and lymphatic vessels, spleen, and skin.  Immune system White blood cells circulate in the blood and lymphatic vessels. The lymphatic system forms a network similar to the blood circulation. It carries a substance called lymph instead of blood. Lymph is a fluid that carries immune-related cells to areas that need them. White blood cells work as a guard against pathogens. When they find germs, they begin to multiply and send signals to other cell types for defending. The body stores white blood cells in different places which are known as lymphoid organs. Major organs of immune system Thymus: The thymus is an organ located in the upper chest where T cells mature. First, lymphocytes (a type of white blood cell) that are destined to become T cells leave the bone marrow and find their way to the thymus where they are then “educated” to become mature T cells.  Major organs of immune system Liver: The liver is the major organ responsible for producing proteins of the complement system. In addition, it contains large numbers of phagocytic cells (a specific type of white blood cell) that ingest bacteria in the blood as it passes through the liver. Bone Marrow: The bone marrow is the location where all cells of the immune system begin their development from stem cells. Tonsils: Tonsils are collections of lymphocytes in the throat. Lymph Nodes: Lymph nodes are collections of B cells and T cells throughout the body. Cells congregate in lymph nodes to communicate with each other. Lymph nodes can become swollen when they are fighting an infection. Spleen: The spleen is a collection of B cells, T cells, and monocytes. It serves to filter the blood and provide a site for invaders/germs and cells of the immune system to interact. Blood: Blood is contained within the circulatory system that carries cells and proteins of the immune system from one part of the body to another. Origins of cells of immune system All cells shown here arise from the hematopoietic stem cell. Platelets – cellular fragments produced by megakaryocytes – are released into the circulation. Polymorphonuclear granulocytes and monocytes pass from the circulation into the tissues. Mast cells are identifiable in all tissues. B cells mature in the fetal liver and bone marrow in mammals, whereas T cells mature in the thymus. The origin of the large granular lymphocytes with natural killer (NK) activity is probably the bone marrow. Lymphocytes recirculate  Types of Immunity  In general, cells of the immune system can be divided into two broad functional categories, which work together to provide innate immunity and the adaptive immune response.  Innate immunity represents an ancient defense system that has evolved to recognize conserved patterns characteristic of a variety of pathogens and often serves as the first line of defense.  Adaptive immunity, a more recent evolutionary innovation, recognizes novel molecules produced by pathogens by virtue of a  How does immune system work particularly? Lymphocytes A lymphocyte is a type of white blood cell that is part of the immune system. There are two main types of lymphocytes: B cells and T cells.  B cells produce the antibodies that target diseased cells,  T cells directly destroy bacteria or cells infected with viruses. There are two types of T cells: Cytotoxic T cells & Helper T cells  How do antibodies work? An antigen is unwanted foreign substance that enters our body. Foreign substances can include bacteria, viruses, fungi, allergens, venom, and other various toxins and disease-causing organisms. An antibody is a protein produced by our immune system to attack and fight off these antigens. Immunoglobulin is used as another word for antibody.  How does immune system work particularly? Complement system The complement system, also known as complement cascade, is a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism. Phagocytic cells/ Phagocytes (neutrophils and monocytes) are immune cells that play a critical role in both the early and late stages of immune responses. Their main role is to circulate and migrate through tissues to ingest and destroy both microbes and cellular debris. At the basic level the broad functions of the complement system can be split into three areas: (1) the activation of inflammation; (2) the opsonization (labeling) of pathogens and cells for clearance/destruction; (3) the direct killing of target cells/microbes by lysis. Phagocytic cells/ Phagocytes (neutrophils and monocytes)  How does immune system work particularly? Complement system- Inflammation The cells of the immune system are widely distributed throughout the body. But if an infection occurs it is necessary to concentrate them and their products to the site of infection. This process is called inflammation.  Changes in blood flow,  An increase in permeability of blood vessels,  The migration of fluid, proteins, and white blood cells (leukocytes) from the circulation to the site of tissue damage. What if inflammation keeps going?  How does immune system work particularly? Complement system- Opsonization Complement components (Opsonins) coat the bacterial surface - opsonization - allowing the phagocytes to recognize the bacteria and engulf them.  How does immune system work particularly? Complement system- Direct Killing  How does immune system work particularly? Cytokines Cytokines are proteins produced by cells, and they serve as molecular messengers between cells. Functions  Stimulate the production of blood cells  Aid in the development, maintenance, and repair of tissues  Regulate the immune system  Drive inflammation through interferons, interleukins, and tumor necrosis factor-alpha (TNF-α)  Vaccination Two key elements: Specificity and memory. Immunization with tetanus toxoid. Chemical modification of tetanus toxin produces a toxoid which has lost toxicity but retains it’s epitopes. Diagnosis  ELISA ELISA (which stands for enzyme-linked immunosorbent assay) is a technique to detect the presence of antigens in biological samples. An ELISA, like other types of immunoassays, relies on antibodies to detect a target antigen using highly specific antibody-antigen interactions. Disease detected by ELISA ▪ HIV ▪ Lyme disease ▪ COVID-19 ▪ Pernicious anemia ▪ Rocky Mountain spotted fever ▪ Squamous cell carcinoma The basic setup of an ELISA assay. A ▪ Syphilis capture antibody on a multi-well plate will immobilize the antigen of interest. This ​ antigen will be recognized and bound by a detection antibody conjugated to biotin and Another advanced technology: Biosensor A biosensor is a device that converts biological phenomena into a recordable signal.