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 Most 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 Occurs 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 normal indigenous flora sources external to the body Modes of Transmission disease causing microbes can be acquired from one of two places 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 HPV Direct 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 Vehicle Transmission Sources of pathogen Wound infections such as tetanus 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 Vector Types Vectors are a type of invertebrate animal that parasitizes a vertebrate animal often blood sucking arthropods mosquitoes fleas ticks lice etc 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 system Pathogen 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 soil Vibrio cholerae 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 Acute Chronic Time Course of Infection Typical Course of Infection Virulence Virulence Virulence the degree or intensity of the ability of a pathogen to cause disease Infectivity Invasiveness Pathogenic potential Degree of signs and symptoms Often measured as LD50 Bacterial Virulence Factors External Structures Cell Wall Membrane Components 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 Streptococcus prevents destruction by certain host immune system chemicals and aides in attachment to host cells used in the attachment of bacteria to surface of host cells Neisseria gonorrhoeae Streptococcus pyogenes Streptococcus pneumoniae Pneumococcus Enzymes Toxins Bacterial Virulence Factors Fimbriae Bacterial Virulence Factors Capsules prevents phagocytosis Bacterial Virulence Factors Cell wall components techoic and lipotechoic acids LPS lipopolysaccharide Bacterial Virulence Factors Mycolic acids Bacterial