Microorganisms and Disease Processes BIOL2010 F24 PDF

www.udst.edu.qa Microorganisms and Disease: Disease Processes Microorganisms and Disease Infectious: a disease caused by an organism that can be transmitted from person to person Communicable Can occur through ingestion, bites, coughs, etc Non-infectious: diseas...

www.udst.edu.qa Microorganisms and Disease: Disease Processes Microorganisms and Disease Infectious: a disease caused by an organism that can be transmitted from person to person Communicable Can occur through ingestion, bites, coughs, etc Non-infectious: diseases caused by genetics, the environment, lifestyle and not disease Non-communicable – cannot be passed from person to person Stress, genetics, allergies, nutritional/metabolic issues Microorganisms and Disease Infectious Agents Can be viruses, bacteria, protozoans, fungi and worms We are only concerned with the first four Process of infection occurs in stages: Exposure to infectious particles Establish a focus of infection Colonize some surface and overcome host defenses Surfaces can be skin or mucosal membranes Skin, gastrointestinal, respiratory, urogenital tract Pathogenicity The pathogenicity of an agent: The ability of a pathogen to cause disease in an organism Pathogenic organisms have differing abilities to cause illness Differing levels of pathogenicity High Pathogenicity – easily cause disease Yersinia pestis, Listeria sp., Clostridium tetani Low Pathogenicity – does not easily cause disease Staphylococcus aureus (opportunistic) Virulence The severity of an illness caused by a pathogen All pathogens cause disease High virulence pathogens cause severe illness Low virulence pathogens cause less severe illness Pathogenicity versus Virulence Pathogens = ability to cause disease Virulence = severity of illness caused by pathogen Virulence All Pathogens can cause disease Pathogens with HIGH virulence cause a severe illness Pathogens with a LOW virulence case less severe illness Example: Colds Common influenza causes fever, cough, sore throat and runny nose Generally over in a matter of days H5N1 causes similar symptoms Contribute to pulmonary failure Pneumonia, multi organ failure H5N1 > virulence than Common influenza Sources of Infection: Reservoirs The variety of sources where infection can be stored until passed to a host A reservoir where the pathogen can survive until transmission Reservoir can be a living or non-living object Common cold can be transmitted by hugging someone Transmission of body fluids can transmit infection Blood, semen, vaginal fluids, saliva, tears Food borne illness Pathogen exists on food item Humans as Reservoirs Pathogens can survive quite happily in humans A person can be an active carrier of infection May not show symptoms Known as an asymptomatic carrier Examples include: Typhoid Fever – consuming infected food Pneumonia – viral/bacterial transmission Polio – can be spread by an immunized individual AIDS – No visible sign of infection Human Carriers - Classifications Passive – carry the pathogen but never show outward sign of the disease Incubatory – can transmit during the incubation period of the disease (measles, mumps, polio) Pathogen is incubating but not evident in carrier Convalescent – can transmit while recovering from the disease (cholera, typhoid fever, diphtheria) Clinically recovered but can still transmit Active – have recovered or does not show the disease but can transmit indefinitely Typhoid Mary – Asymptomatic Carrier Animals as Reservoirs Microorganisms can infect both humans and animals Transmission from animal to human = zoonoses Monkeys can act as a reservoir for malaria Cats can act as a reservoir for disease Toxoplasmosis/rabies Toxoplasma gondii and rabies virus Dogs can act as reservoirs for disease Toxocariasis – roundworms Ringworm – fungal Rabies – rabies virus Non-Living Reservoirs Soil – bacterial transmission – Clostridium sp. Tetanus, gangrene Water – Vibrio cholera – secretes a toxin Extreme diarrhea and dehydration Cryptosporidium – weight loss, nausea, diarrhea Air – Anthrax, chicken pox, Influenza, measles, TB Portals of Entry/Exit Portals of Entry An MO has to enter tissues to cause an infection Entry points are called portals of entry Examples: Eyes, ears, cuts, abrasions, mouth Portal of Exit Disease spreads when infectious agents leave the host All exit points are called portals of exit Examples: Eyes, ears, anus, mouth, blood/body fluids Modes of Transmission Transmission of a disease occurs when a reservoir spreads infection from a portal of exit to a portal of entry Passed on to another organism There are three means of transmission: 1. Contact 2. By vehicles 3. By vectors Disease Transmission Contact Transmission Contact: occurs when an infectious disease is transmitted from an infected individual to a new host. Contact can be: Indirect Direct Droplet Contact Transmission Direct occurs from body contact Horizontal – shaking hands, kissing, sexual contact Vertical – from parent to offspring via egg/sperm, through the placenta, breast milk or birth canal Example: Herpes Simplex I &II Baby is exposed traveling through birth canal Fecal-Oral – unwashed hand to mouth transfer Contract Transmission Indirect occurs from contact with non- living objects Also called fomites Examples include soiled tissue, gloves, dishes, doorknobs, eating utensils, toys, soap, lipstick, lip gloss, money Contact Transmission Contact: occurs when an infectious disease is transmitted from an infected individual to a new host. Droplet – obtained from the aerosol from sneeze, cough or talking to an infected individual A proximity of ~1 m is sufficient for transfer Vehicle Transmission Vehicle: non-living carrier of a pathogen From reservoir to a host Waterborne diseases - cholera Airborne transmission - flu Food borne transmission - salmonella Vector Transmission Vector: transfer from reservoir to host via a living organism Examples include: Mosquitos – Plasmodium (malaria) Fleas – Yersinia pestis – bubonic plague Lice – mange/dermodectic mange Flies – Trypanosomiasis – African Sleeping Sickness Nosocomial Transmission Nosocomial Infections – a type of infection acquired in a health care facility Secondary to the original condition Appear shortly after admission or within 14 days of discharge Iatrogenic Infections – infections that are the result of medical treatment Caused by healthcare workers, surgeons, or physicians Cross infection of patients, materials from surgery left behind Nosocomial Infections Most common is the bacterium Staphylococcus aureus. Other examples: Escherichia coli, Enterococci, Candida Normally found on the skin and mucous membranes. Antibiotic-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA) can be especially dangerous and difficult to treat. How do bacteria cause Disease? Virulence Factors Structural or physiological characteristics that help the organism cause infection. Adherence – How a pathogen ‘sticks’ to a target cell/tissue. Evasion – How a pathogen can escape the hosts immune system defenses. Toxins – How a pathogen damages cells/tissue Bacterial Infection - Adherence Capsule - Antiphagocytic Pili (fimbriae) - Antiphagocytic Adhesins – Proteins or glycoproteins that are found on attachment pili (fimbriae) that allow the bacteria to attach to specific receptors on target cells Just sticking to the surface of the cells is often not enough to cause infections, there needs to be other characteristics or factors acting as well. Bacterial Infection - Evasion Invasiveness Hyaluronidase (Enzyme) breaks down material that holds tissues together separating cells allowing bacterial to penetrate deeper into tissues. Evasiveness Coagulase (Enzyme) allows bacteria to coagulate blood cells, effectively protecting them from the immune system allowing them to reproduce unhindered. Streptokinase (Enzyme) breaks down coagulated blood (clots). Bacteria Infection - Toxins Endotoxin Part of the cell wall of many Gram-Ve bacteria that are released when the bacteria is killed or dies or divides. Not as acute or severe, cause general symptoms such as as fever, drop in blood pressure or tissue damage. Salmonellosis, Tularemia, Endotoxic shock Exotoxin Soluble substance secreted into host tissues. Produced by several Gram Positive and some Gram negative bacteria More powerful toxins, can be enzymes such as Hemolysins, Leukocidins. Botulism, Tetanus, Cholera, Plague