Chapter 16: Mechanisms of Infectious Disease

Infectious Disease
the disease state brought about by the interaction with another organism
any organism capable of supporting the nutritional and physical growth requirements of another
the presence and multiplication of a living organism on or within the host. An example, at the onset of a cold, a respiratory virus causes illness, it has colonized and is multiplying
the bacteria inhabiting exposed surfaces of the body. An example would be micro-organisms found on the surface of your skin
micro-organisms so virulent that they are rarely found in the absence of disease
free-living organisms obtaining their growth from dead or decaying organic material from the environment. There are typically harmless but like all micro-organisms including normal flora, they too can cause opportunistic disease in a weaken host
the organism has disease-inducing potential
the microorganism and the host both derive from the interaction, for example the flora of the gut
a situation where organisms acquire nutrition needs and shelter but the host body is not affected for example normal skin flora
a situation whereby only the invasive organism benefits from the relationship for example, a tapeworm
protein particles that have the capability to cause infectious disease but are unique that they do not contain RNA and DNA or a genetic master plan when reproducing or coding for essential proteins and enzymes necessary in most cases for survival, Examples: Creutzfeldt-Jakob disease and Mad Cow disease. They typically cause neuronal degeneration, ataxia, dementia and death
are the smallest pathogens, they are unique as they have no organized cellular structure, they have a protein coat surrounding a nucleic acid core of DNA or RNA, but never both, incapable of replication outside a living cell, they depend on living cells for reproduction. Examples: Rotovirus', herpes virus', CMV, EB virus
infect and cause diseases in animals and humans. Animals can also transmit disease to humans by parasitic infection. Protozoans (transmitted by sexual contact, food water or arthropod vector such as through a mosquito) Examples: malaria, amebic dysentery, Helminths (roundworms, tapeworms, flukes etc.) Arthropods (ticks, mosquito, flea vectors)
classified according to microscopic appearance, as either aerobic or anaerobic, according to staining of the cell
Rickettsiaceae, Anaplasmataceae, Chlamydiaceae, and Coxiellai
oraganisms that combine charateristics of viral and bacterial agents to produce disease in humans. Obligate intracellular pathogens like the viruses, produce a rigid peptidoglycan cell wall, reproduce asexually by cellular division, contain RNA and DNA similar to the bacteria
saprophytes found on all creatures and part of the normal flora of humans, they are usually harmless however can cause disease in a weakened host, for example: dermatophytes, ringworms, candida albicans, they are divided into two groups: yeast and molds that reproduce by budding, because their cell wall is unlike bacteria, antibiotics do not work
the study of factors, agents and circumstances that influence the transmission of infectious disease among humans
the number of new case of an infectious disease that occur within a defined population
the number of active cases at any given time
found in a particular geographic region, the incidence and prevalence are expected relatively stable
abrupt and unexpected increase in the incidence of disease over endemic rates
spread of disease beyond continental boundaries
Organisms Portal of Entry
penetration-disruption of bodily integrity causing potential for invasion i.e. surgical incision, cut. Direct contact-exposure of pathogens with intact membranes i.e. STDs. Ingestion-invasion via oral or GI pathway. Inhalation-invasion by inhalation i.e. bacterial PNA, meningitis (2), TB, flu, measles, mumps, chicken pox, the common cold
Infectious Disease defined by Location
Nosocomial infection develop in hospitalized patients. Community-acquired infections are acquired outside of healthcare facilities. A host may be the victim or an object, or substance from which the infectious agent was acquired
reflects the site of infection (e.g., diarrhea, rash, convulsions, hemorrhage, pneumonia)
can be shared by a number of diverse infectious diseases (e.g., symptoms such as fever, myalgia, headache)
predictable patterns (e.g., chicken pox and measles)
may require lab testing to detect (e.g., hepatitis or increased white blood cell count)
Incubation Period
phase during which the pathogen begins active replication without producing recognizable symptoms in the host, the duration can be long or short in some cases
Prodromal Stage
initial appearance of symptoms in the host, although the clinical presentation during this time may be only a vague sense of malaise. The host may experience mild fever, myalgia, headache, and fatigue. The duration can vary considerably from host to host.
Acute Stage
period which the host experiences the maximum impact of the infectious process corresponding to rapid proliferation and dissemination of the pathogen. During this phase, toxic byproducts of microbial metabolism, cell lysis, and the immune response mounted by the host combine to produce tissue damage and inflammation. The symptoms of the host are pronounced and more specific than in the prodromal stage, usually typifying the pathogen and sites of involvement
Convalescent Stage
characterized by by the containment of infection, progressive elimination of the pathogen, repair of damaged tissue, and resolution of associated symptoms. The duration can either long or short depending on the type of pathogen and the voracity of the host's immune system.
Resolution Stage
the total elimination of a pathogen form the body without residual signs or symptoms of disease
Virulence Factors
substances or products generated by infectious agents that enhance the ability to cause disease
proteins released during bacteria growth that damage/kill host cells (botulism, tetanus, diptheria)
potent activators from gram negative bacteria that cause problems such as endotoxemia
Adhesion Factors
no interaction between microorganisms and humans can progress to infection or disease if the pathogen is unable to attach to and colonized the host
Evasive Factors
work to counteract the immune system or take advantage of immune incompetence (H. pylori, HIV)
Invasive Factors
penetrate anatomical barriers allowing entry
Antibacterial Agents
usually called antibiotics. Most antibiotics are usually produced by other microorganisms, primarily bacteria and fungi, as byproducts of metabolism and usually are effective only against other prokaryotic organisms
Antiviral Agents
viral replication requires the use of eukaryotic host cells enzymes, and the drugs that effectively interrupt viral replication are likely to interfere with host cell reproduction as well
Anti-fungal Agents
the target site of the two most important families are the cytoplasmic membranes of yeast or molds, they differ from human cells membranes in that they contain the sterol ergosterol instead of cholesterol
Anti-parasitic Agents
because of the extreme diversity of human parasites and their growth cycles, a review of therapies and agents would be highly impractical and lengthy. Similar to other infectious diseases caused by eukaryotic microorganisms, treatment of parasitic illnesses is based on exploiting essential components of the parasite's metabolism or cellular anatomy that are not shared by the host
Bacterial Resistance Mechanisms
inactivate antibiotics, genetically alter antibiotic binding sites, bypass antibiotic activity, changes in bacterial cell wall of bacteria cause resistance
Intravenous Immunoglobin & Cytokine Therapy
methods supplementing or stimulation the host's immune response so that the spread of a pathogen is limited or reversed from example, the use of IgG IV. Pathogen-specific antibodies infusions facilitate neutralizations, phagocytosis, and clearance of infectious agents above and beyond the capabilities of the diseased host
Nonpharmacologic Intervention
providing access to an infected site by antimicrobial agents (drainage of an abscess), cleaning of the site (debridement), removing infected organ or tissue (e.g., appendectomy)
Antibiotic Mechanisms
inference with a specific step in bacterial cell wall synthesis, inhibition of bacterial protein synthesis, interruption of bacterial nucleic acid synthesis, interference with normal bacterial metabolism
causes irreversible and lethal damage to the bacterial pathogen
inhibitory effects on bacterial growth are reversed when the agent is eliminated
Category A Agents
plague, tularemia, smallpox, hemorrhagic fever viruses
Category B Agents
agents of food-borne and water-borne disease, zoonotic infections, viral encephalitides, toxins from castor bean
Category C Agents
mycobacterium tuberculosis, nipah virus and hantavirus, tick-borne and yellow fever viruses, cryptosporidium parvum