A small organism which lives within or upon a larger organism of a different species at whose expense it obtains some advantage
Parasite
The larger organism that is parasitized
Host
Entrance, mulitplication, and colonization of a host--need not cause disease and may be "normal flora"
Infection
The agent that causes disease
Etiological Agent
The disease producing organism
Pathogen
A parasite that ordinarily does not cause disease. Occurs in compromised host
Opportunist (Opportunistic Infection)
Sequence of Infection (4)
Exposure
Multiplication
Recovery/Death
Convalescence
Period prior to the development of symptoms (days to weeks)
Incubation Period
The very first symptoms of an infection
Prodrome
Symptoms when disease is fully manifest
Syndrome
Shortly after eradication of an infection
Convalescence
The method for entry of the pathogen into the body
Transmission
First and most important step in infection. Involves contact with a mucosal cell surface molecule (receptor). Involves specificity, antagonism, and synergy
Adherence
Study of how a disease is transmitted (geographical distribution, animal reservoirs, season occurence)
Epidemiology
Routes of Transmission (5)
Direct contact
Aerosol droplets
Fomites
Ingestion
Arthropod vectors
True or False:
Adherence molecules extend from bacterial surface as lipoteichoic acid, proteins, and carbohydrates
True
Degree of virulence is measured by (3)
Minimal Lethal Dose (MLD)
Lethal Dose50 (LD50)
Infectious Dose50 (ID50)
Smallest dose that will result in death of the host
minimal lethal dose (MLD)
Dose that kills 50% of infected hosts
Lethal Dose50
Dose that infects 50% of treated hosts
Infectious Dose50
Ability to cause disease
Pathogenicity
Ability to invade tissues and multiply
Invasiveness
Antibody with phagocytosis and killing of pathogen
Extracellular Pathogen
Cell-mediated immunity
Intracellular pathogen
Mechanisms to avoid host defenses by extracellular bacterial pathogens
Capsules (anti-phagocytic)
Fimbriae (adherence)
M-protein (anti-phagocytic)
B cells produce specific antibodies (with Th2 cells) that _____ bacteria
Opsonize
______ can also opsonize bacteria
Complement
Phagocytosis can happen via (3)
Chemotaxis
Engulfment
Intracellular killing
These parasites require an intracellular environment. Examples include rickettsia, chlamydia, and viruses
Obligate intracellular parasites
These parasites grow intracellularly or on artificial media. Examples include mycobacteria, salmonella, brucella, legionnaire's disease, & listeria
Faculatative Intracellular Parasites
How do intracellular pathogens avoid host defenses?
by preventing intracellular killing
Secreted from bacterial cells into the surrounding medium
Exotoxins
Neurotoxin producing flaccid paralysis
Botulism
Neurotoxin producing spastic paralysis
Tetanus
Causes cells of the body to produce large amounts of cytokines
Toxic Shock Syndrome Toxin
Enterotoxin--activates adenyl cyclase
Cholera Toxin
Part of the cell wall of Gram-negative bacteria. Activates macrophages causing them to make IL-1, TNF-alpha, and IL-6. Fever, hypotension, DIC. Lethal shock can occur
Endotoxins
The number of cases or incidence of a specific notifiable disease per unit population
Morbidity Rate
The number of deaths due to a specific notifiable disease per unit population