Microbiology Exam 1 Study Guide: Infectious Diseases, Respiratory and Nervous System Infections

Chapter 9: Principles of Infectious Disease and Epidemiology

Key Concepts in Infectious Disease

• Opportunistic vs. True Pathogen: Opportunistic pathogens cause disease only in hosts with compromised defenses, while true pathogens can cause disease in healthy individuals.

• Communicable vs. Noncommunicable Disease: Communicable diseases can be transmitted from person to person (e.g., influenza), whereas noncommunicable diseases are not spread between hosts (e.g., tetanus).

• Acute vs. Chronic Disease: Acute diseases have rapid onset and short duration (e.g., common cold), while chronic diseases develop slowly and persist over time (e.g., tuberculosis).

• Endemic vs. Sporadic Disease: Endemic diseases are constantly present in a population (e.g., malaria in some regions), while sporadic diseases occur infrequently and irregularly.

Pandemic vs. Epidemic

• Pandemic: A global outbreak of disease affecting a large number of people across multiple continents (e.g., COVID-19).

• Epidemic: A sudden increase in cases of a disease above what is normally expected in a specific area.

Emerging vs. Reemerging Diseases

• Emerging Disease: A disease that is newly identified in a population or has recently increased in incidence.

• Reemerging Disease: A disease that was previously under control but is now increasing in incidence again (e.g., measles outbreaks).

Herd Immunity

• Definition: When a high percentage of a population is immune to a disease (through vaccination or previous infection), the spread of the disease is limited, protecting those who are not immune.

• Application: Critical for controlling outbreaks of communicable diseases.

Stages of Infectious Disease

• Incubation Period: Time between exposure and onset of symptoms.

• Prodromal Phase: Early, mild symptoms appear.

• Acute Phase: Disease is at its most severe.

• Period of Decline: Symptoms subside as the immune response controls the infection.

• Convalescent Period: Recovery and return to normal health.

• Variation: The length and severity of each stage can differ by pathogen, complicating diagnosis and epidemiological tracking.

Carriers

• Chronic Carrier: Harbors the pathogen for extended periods, potentially spreading disease long-term (e.g., Typhoid Mary).

• Asymptomatic Carrier: Infected but shows no symptoms, yet can transmit the pathogen to others.

Epidemiology

• Definition: The study of the distribution and determinants of health-related states in populations.

• Primary Goals: 1) Identify the cause of diseases and risk factors, 2) Control and prevent disease spread.

Quarantine

• Definition: Restricting the movement of individuals who may have been exposed to a contagious disease.

• Effectiveness: Useful when individuals may be infectious before symptoms appear or when diseases are highly contagious.

Prevalence and Incidence Rates

• Prevalence Rate: The total number of cases (new and existing) in a population at a given time.

• Incidence Rate: The number of new cases in a population during a specific period.

• Formulas:

$\text{Prevalence} = \frac{\text{Total number of cases}}{\text{Total population}} \times 100,000$

$\text{Incidence} = \frac{\text{Number of new cases}}{\text{Population at risk}} \times 100,000$

• Factors Impacting Prevalence: Duration of disease, recovery rate, mortality, and new case rate.

Key Terms

• Population: The group of individuals being studied.

• Morbidity: The state of being diseased or the number of cases of illness in a population.

• Mortality: The number of deaths caused by a disease in a population.

Healthcare-Associated vs. Community-Acquired Infections

• Healthcare-Associated Infection (HAI): Acquired in a healthcare setting (e.g., hospital-acquired MRSA).

• Community-Acquired Infection: Acquired outside of healthcare settings.

• Prevention: Hand hygiene, sterilization, isolation protocols, and vaccination.

Chapter 16: Respiratory System Infections

Defense Mechanisms of the Respiratory System

• Physical Barriers: Mucus, cilia, and the mucociliary escalator trap and remove pathogens.

• Immune Defenses: Secretory IgA, alveolar macrophages, and normal flora inhibit pathogen colonization.

Normal Flora of the Respiratory System

• Location: Upper respiratory tract (nose, throat).

• Examples: Streptococcus spp., Staphylococcus spp., Corynebacterium spp.

Terminology in Respiratory Infections

• Rhinitis: Inflammation of the nasal mucosa.

• Pharyngitis: Inflammation of the throat.

• Laryngitis: Inflammation of the larynx.

• Pneumonia: Infection of the lungs.

Comparison of Common Respiratory Illnesses

Disease	Symptoms	Notes
Common Cold	Sneezing, runny nose, mild sore throat	Usually caused by rhinoviruses; no vaccine available
RSV	Cough, wheezing, difficulty breathing	Serious in infants and elderly
HPIV	Croup (barking cough), fever	Common in children
Influenza	Fever, chills, muscle aches, cough	Annual vaccine recommended

Vaccines and Respiratory Viruses

• Annual Flu Vaccine: Needed due to antigenic drift and shift in influenza viruses, leading to new strains each year.

• No Cold Vaccine: The common cold is caused by many virus types, making vaccine development impractical.

Severe Acute Respiratory Syndrome (SARS)

• Definition: A severe viral respiratory illness caused by a coronavirus (SARS-CoV).

• Symptoms: High fever, cough, shortness of breath, and pneumonia.

Typical vs. Atypical Pneumonia

• Typical Pneumonia: Caused by bacteria like Streptococcus pneumoniae; rapid onset, productive cough.

• Atypical Pneumonia: Caused by organisms like Mycoplasma pneumoniae; milder symptoms, dry cough.

Otitis Media in Children

• Reason for Susceptibility: Children's Eustachian tubes are shorter and more horizontal, facilitating pathogen entry from the throat to the middle ear.

Diseases Caused by Streptococcus pyogenes

• Strep throat (pharyngitis)

• Scarlet fever

• Rheumatic fever

• Necrotizing fasciitis

Tuberculosis

• Causative Agent: Mycobacterium tuberculosis

• Forms: Latent TB (no symptoms, not contagious), Active TB (symptomatic, contagious)

Organisms Causing Typical Pneumonia

• Streptococcus pneumoniae: Most common cause; leads to productive cough and fever.

• Haemophilus influenzae: Can cause severe pneumonia, especially in children and elderly.

• Klebsiella pneumoniae: Associated with hospital-acquired infections.

Chapter 18: Nervous System Infections

Blood-Brain Barrier and Molecular Transport

• Blood-Brain Barrier (BBB): A selective barrier formed by endothelial cells that restricts passage of substances from the bloodstream into the brain.

• Molecular Transport: Only small, lipid-soluble molecules and certain nutrients can cross; pathogens must have special mechanisms to breach the BBB.

Viral vs. Bacterial Meningitis

• Viral Meningitis: Generally less severe, caused by enteroviruses; often self-limiting.

• Bacterial Meningitis: More severe, rapid progression; requires urgent antibiotic treatment.

Polio: Signs and Symptoms

• Fever, sore throat, headache

• Muscle weakness, paralysis (in severe cases)

• Most infections are asymptomatic or mild

Bacterial Meningitis: Causative Agents

• Neisseria meningitidis: Meningococcal meningitis

• Streptococcus pneumoniae: Pneumococcal meningitis

• Haemophilus influenzae type b: Hib meningitis (mainly in children)

Leprosy: Lepromatous vs. Tuberculoid Forms

• Lepromatous Leprosy: More severe, widespread skin lesions, high bacterial load.

• Tuberculoid Leprosy: Milder, localized lesions, low bacterial load.

Tetanospasmin vs. Botulinum Toxin

Toxin	Source	Effect	Symptoms
Tetanospasmin	Clostridium tetani	Blocks inhibitory neurotransmitters	Muscle spasms, lockjaw
Botulinum toxin	Clostridium botulinum	Blocks acetylcholine release	Flaccid paralysis

Arboviruses and Nervous System Infections

• Arboviruses: Arthropod-borne viruses (e.g., West Nile virus) transmitted by mosquitoes or ticks.

• Mechanism: Enter bloodstream via bite, cross BBB, cause encephalitis or meningitis.

Toxoplasmosis

• Causative Agent: Toxoplasma gondii (a protozoan parasite)

• Transmission: Ingestion of oocysts from contaminated food, water, or cat feces.

• Effects: Usually mild in healthy individuals; can cause severe disease in immunocompromised patients and congenital infections in fetuses.

Additional info: These notes are based on the exam study guide and expanded with academic context to provide a comprehensive review for exam preparation. Students are encouraged to consult their textbook and class materials for further details and examples.