Infection and Disease Host-Microbe Relationship Symbiosis : a close association between two species of organism Mutualism both species directly benefit example intestinal microbes of many animals Marine nematode and sulfide oxidizing bacteria Host-Microbe Relationship Commensalism one species benefits, the other neither benefits or is harmed example skin bacteria, many intestinal microbes, dental plaque microbes Parasitism one species benefits, the other is harmed disease causing microbes (pathogens) many levels of parasitism mild harm death of host Normal (Indigenous) Microflora Concepts Human body surfaces habitat for many microbes microbes either mutualists or commensals All may be mutualists indirectly by: out competing pathogens for space and nutrients normally not parasites (pathogens) Normal (Indigenous) Microflora žMost have preferred residence on the human body!resident microflora = always present on host!transient microflora= only present under certain conditions or at certain times Indigenous microbes as opportunistic pathogens žOccurs when:!—numbers increase greatly over normal!○Candida albicans, Clostridium difficile! Indigenous microbes as opportunistic pathogens Occurs when: gain entrance into sterile areas of the body portions urinary tract portions reproductive tract lower respiratory tract blood and other body fluids subcutaneous and connective tissues host has failure of immune system (immunocompromised) Disease Transmission General Concepts disease causing microbes can be acquired from one of two places: normal indigenous flora sources external to the body Modes of Transmission 1) Contact Transmission - spread of disease from one host to another by close contact 2) Vehicle Transmission - spread of disease from host to host by means of a non-living substance acting to transport the pathogen. 3) Vector Transmission - spread of disease from host to host by means of a living organism (the vector) acting to transport the pathogen Contact Transmission 1) Communicable Disease spread of disease from one human to another Direct Contact Transmission Sexually Transmitted (STD or venereal) gonorrhea, genital herpes, AIDS,HPVDirect Fecal-Oral shigellosis, hepatitis A Vertical Transmission syphilis, AIDS, chicken pox Indirect Contact Transmission Droplet common cold, influenza Fomites nonliving objects intestinal “flu”, salmonella Contact Transmission 2) Zoonotic Disease - spread of disease from animals to humans Animal Bites rabies Contact with infected animal tissue, fluids, feces leptospirosis, tularemia 3) Non-communicable Fomites Wound infections such as tetanus Vehicle Transmission Sources of pathogen Infected organism sheds the pathogen Contamination of vehicle may be from either human or animal (zoonotic) source Inanimate object sheds the pathogen air conditioning systems, fungi growing on walls Stachybotrys Vehicle Transmission Types: 1) Waterborne Transmission (indirect fecal-oral) water contaminated with fecal material usually gastrointestinal diseases rotavirus infections, Giardia infections, Vibrio cholerae infection, salmonellosis!2)Airborne Transmission (aerosol transmission)!○microscopic particles (aerosols) containing pathogen suspended in the air; travels farther than 1 meter!○usually respiratory diseases!—tuberculosis, influenza, fungal infections Vehicle Transmission Types (cont.): 3) Foodborne Transmission food contaminated with pathogens and/or their toxins usually gastrointestinal diseases salmonella infections, staphylococcus food poisoning, hepatitis A, Norovirus Vector Transmission Vectors are a type of invertebrate animal that parasitizes a vertebrate animal. often blood sucking arthropods (mosquitoes, fleas, ticks, lice, etc.) Vector Types Mechanical Vectors - vector is physically contaminated with the pathogen and only serves to carry the pathogen to a new host Biological Vectors - vector is a required part of the life cycle of the pathogen; for disease transmission to occur the pathogen must replicate or undergo some developmental change within the vector Malaria Life Cycle Vector Transmission Types of Vector Transmitted Disease Non-Communicable Disease Infected Person Vector Person Malaria Epidemic typhus Zoonotic Disease Infected Animal Vector Person Lyme disease, murine typhus Factors Involved in Disease Transmission Host Characteristics: number of hosts, host immune systemPathogen Characteristics number of pathogens (ID50), virulence of pathogen Environment moisture, temperature, other physical factors vector and/or reservoir present if needed for transmission Where are Pathogens when not causing human disease? Reservoirs: places where human pathogens persist and serve as a source of infection Types of Reservoirs Animal Reservoirs pathogen persists in animal population. pathogen may or may not cause disease in the reservoir animal pathogen transmitted to humans when human come in proximity of the animal reservoir Examples encephalitis viruses and various bird reservoirs, rabies Human Reservoirs Carriers: persons who harbor a human pathogen without having the disease can be chronic or intermittent carriers Examples typhoid, polio, some staphylococcal disease Non-Living Reservoirs water Vibrio cholerae soil tetanus, fungi pathogens Mechanism of Infectious Disease How do microorganisms cause disease? Basic Events: Gain access to host Multiply within host Overcome host defense mechanisms Effect/Damage host tissues Disease Mechanisms Methods of Tissue Damage toxins enzymes reaction of host immune system to pathogen Patterns of Damage Local Systemic Time Course of Infection Acute Chronic Typical Course of Infection Virulence žVirulence the degree or intensity of the ability of a pathogen to cause disease —Infectivity ---Invasiveness ---Pathogenic potential -(Degree of signs and symptoms) žOften measured as LD50 Virulence Virulence Factor - a specific characteristic or aspect of a pathogen that is responsible (either in whole or in part) for the pathogens ability to cause disease. Bacterial Virulence Factors External Structures Cell Wall/Membrane ComponentsEnzymes Toxins Bacterial Virulence Factors Fimbriae used in the attachment of bacteria to surface of host cells Neisseria gonorrhoeae, Streptococcus pyogenes Bacterial Virulence Factors Capsules prevents phagocytosis Streptococcus pneumoniae (Pneumococcus) Bacterial Virulence Factors