ch. 14 Symbiotic Relationships and Infectious Diseases
Symbiotic Relationships Between Microbes and Their Hosts
Symbiosis: Meaning "to live together"; refers to the relationship between various microorganisms and their human hosts.
Types of Symbiosis
Mutualism: Both organisms benefit.
Example: Bacteria in human colon (aid in digestion).
Commensalism: One organism benefits while the other is neither helped nor harmed.
Example: Mites in human hair follicles.
Amensalism: One organism is harmed, the other is unaffected.
Example: Fungus secreting antibiotics that inhibit nearby bacteria.
Parasitism: One organism benefits at the expense of the other.
Example: Tuberculosis bacteria in human lungs.
Microbiome of Humans
Definition: Organisms that colonize body surfaces without causing disease.
Terms:
Normal microbiota / Normal flora / Indigenous microbiota
Types:
Resident microbiota: Permanently in the body, usually commensal.
Transient microbiota: Temporary inhabitants, do not persist.
Resident Microbiota Characteristics
They play significant roles in digesting food and protecting against pathogens.
Develop during the birthing process and establish mainly in the first months of life.
Acquisition of the Microbiome
Started in the womb (sterile environment).
Development continues during birth and beyond, influenced by environmental exposures.
Opportunistic Pathogens
Definition: Normal microbiota that cause disease under specific circumstances.
Conditions that allow opportunistic infections:
Introduction to an unusual site in the body.
Body's immune suppression.
Changes in normal microbiota due to antibiotics.
Stressful conditions affecting the host.
Reservoirs of Infectious Diseases
Definition: Locations where infectious agents normally live and multiply.
Types of Reservoirs
Animal Reservoirs: Zoonoses that are diseases transferred from animals to humans.
Example: Tapeworm from dogs, malaria from monkeys, rabies from bats.
Human Carriers: Asymptomatic individuals who can transmit diseases.
Can be healthy carriers or become symptomatic.
Nonliving Reservoirs: Infections may arise from soil, water, and food.
Often due to contamination with fecal/urine microorganisms.
Infection and Contamination
Contamination: Presence of microbes on the body without causing disease.
Infection: When microbes evade the immune system, multiply, and establish in the host.
Portals of Entry for Pathogens
Skin: Barrier breached through cuts, openings, or burrowing pathogens.
Mucous membranes: Primarily through the respiratory tract, gastrointestinal tract, or urogenital tract.
Placenta: Sometimes pathogens can cross and affect the fetus.
Parenteral route: Entry via injection or trauma bypasses normal portals.
Adhesion in Infection
Adhesion: Critical for establishing infections; pathogens utilize structures like adhesins to latch onto host cells.
Biofilms: Some pathogens can form biofilms, aiding in colonization and persistence.
Nature of Infectious Disease
Infection: Invasion of host by pathogen leading to changes in normal body functions.
Disease: Results from these alterations, often referenced as morbidity.
Disease Manifestations
Symptoms: Subjective; perceived by the patient (e.g., pain, fatigue).
Signs: Objective; measurable manifestations (e.g., fever).
Syndrome: A set of symptoms and signs that characterize a specific condition.
Causation of Disease
Etiology: Study of causes of diseases; may involve infections, genetic factors, lifestyle.
Koch’s Postulates: A systematic method to establish the causative agent of an infectious disease.
Virulence Factors: Attributes that enable pathogens to cause disease (e.g., toxins, adhesion factors).
Stages of Infectious Disease
Incubation Period: No symptoms; pathogen multiplies.
Prodromal Period: Vague symptoms appear.
Illness: Most severe signs and symptoms present.
Decline: Symptoms subside.
Convalescence: Recovery and return to normal health.