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

Chapter 9: Principles of Infectious Disease and Epidemiology

Key Definitions and Concepts

• Opportunistic Pathogen: A microorganism that causes disease only when the host's defenses are compromised.

• True Pathogen: An organism capable of causing disease in healthy individuals.

• Communicable Disease: An infectious disease that can be transmitted from one host to another.

• Noncommunicable Disease: A disease that is not transmitted from person to person.

• Acute Disease: Disease with rapid onset and short duration.

• Chronic Disease: Disease that develops slowly and persists over a long period.

• Endemic Disease: Disease constantly present in a population or region.

• Sporadic Disease: Disease that occurs occasionally and at irregular intervals.

• Pandemic: An epidemic that spreads over several countries or continents, affecting a large number of people.

• Epidemic: A sudden increase in the number of cases of a disease above what is normally expected in a population.

• Emerging Disease: A disease that is new or increasing in incidence.

• Reemerging Disease: A disease that was previously under control but is now increasing in incidence again.

• Herd Immunity: When a high percentage of the population is immune to a disease (through vaccination or previous infection), reducing its spread.

• Chronic Carrier: An individual who harbors a pathogen for a long time and can transmit it, often without symptoms.

• Asymptomatic Carrier: An individual who carries and spreads a pathogen but does not show symptoms.

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

• Quarantine: The separation and restriction of movement of people who may have been exposed to a contagious disease.

• Population: The group of individuals being studied.

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

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

• Healthcare-Acquired Infection (HAI): Infections acquired in healthcare settings.

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

Comparisons and Classifications

• Opportunistic vs. True Pathogen: Opportunistic pathogens require a compromised host; true pathogens can infect healthy hosts.

• Communicable vs. Noncommunicable Disease: Communicable diseases spread between hosts; noncommunicable do not.

• Acute vs. Chronic Disease: Acute is rapid and short; chronic is slow and long-lasting.

• Endemic vs. Sporadic Disease: Endemic is consistently present; sporadic occurs irregularly.

Pandemic vs. Epidemic

• Pandemic: Global outbreak (e.g., COVID-19).

• Epidemic: Local or regional outbreak (e.g., Ebola in West Africa).

Emerging vs. Reemerging Diseases

• Emerging: New or rapidly increasing (e.g., Zika virus).

• Reemerging: Previously controlled, now increasing (e.g., measles).

Herd Immunity

• Protects non-immune individuals when a critical portion of the population is immune.

• Reduces the likelihood of disease spread.

Stages of Infectious Disease

1. Incubation Period: Time between infection and symptom onset.

2. Prodromal Phase: Early, mild symptoms.

3. Acute Phase: Peak of disease symptoms.

4. Period of Decline: Symptoms subside as immune response overcomes pathogen.

5. Convalescent Phase: Recovery and return to normal.

• Duration and intensity of each stage can vary by pathogen, complicating diagnosis and control.

Carriers

• Chronic Carrier: Long-term harboring and shedding of pathogen.

• Asymptomatic Carrier: No symptoms but can transmit disease.

Epidemiology: Goals and Definitions

• Primary Goals: Identify causes of disease and control/prevent their spread.

Quarantine

• Used to limit disease spread when exposure is suspected but infection is not confirmed.

• Effective for diseases with long incubation periods or high transmission rates.

Prevalence and Incidence Rates

• Prevalence Rate: Proportion of a population with a disease at a specific time.

• Incidence Rate: Number of new cases in a population over a period of time.

Formulas:

• Prevalence Rate: $\text{Prevalence} = \frac{\text{Total cases}}{\text{Total population}} \times 100$

• Incidence Rate: $\text{Incidence} = \frac{\text{New cases}}{\text{Population at risk}} \times 100$

• Factors impacting prevalence: duration of disease, recovery rate, mortality, and new case rate.

Healthcare-Acquired vs. Community-Acquired Infections

• HAIs: Acquired in hospitals/clinics; often involve antibiotic-resistant organisms.

• Community-Acquired: Acquired outside healthcare settings.

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

Chapter 16: Respiratory System Infections

Factors Limiting Respiratory Infections

• Mucociliary escalator (cilia and mucus trap and remove microbes).

• Normal flora outcompete pathogens.

• Immune defenses (e.g., IgA antibodies, alveolar macrophages).

Normal Flora of the Respiratory System

• Upper respiratory tract harbors normal flora (e.g., Streptococcus spp., Staphylococcus spp., Corynebacterium spp.).

• Lower respiratory tract is typically sterile.

Terminology: Respiratory Inflammation and Infections

• Rhinitis: Inflammation of the nasal mucosa.

• Pharyngitis: Inflammation of the pharynx.

• Laryngitis: Inflammation of the larynx.

• Bronchitis: Inflammation of the bronchi.

• Pneumonia: Infection of the lungs.

Comparison of Common Respiratory Infections

Disease	Symptoms	Notes
Common Cold	Sneezing, runny nose, mild cough	Usually caused by rhinoviruses; no vaccine
RSV	Severe in infants; wheezing, difficulty breathing	Respiratory Syncytial Virus; can cause bronchiolitis
HPIV	Croup (barking cough), fever	Human Parainfluenza Virus; affects young children
Influenza	Fever, chills, muscle aches, cough	Annual vaccine needed due to antigenic drift/shift

Vaccines and Immunity

• Annual flu vaccines are needed due to frequent changes in influenza virus antigens (antigenic drift and shift).

• No vaccine for the common cold due to high number of causative viruses and antigenic diversity.

Severe Acute Respiratory Syndrome (SARS)

• Caused by a coronavirus (SARS-CoV).

• Symptoms: high fever, cough, shortness of breath, pneumonia.

• Transmitted via respiratory droplets.

Typical vs. Atypical Pneumonia

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

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

Otitis Media in Children

• Children have shorter, more horizontal Eustachian tubes, making them prone to middle ear infections after colds.

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)

• Symptoms: chronic cough, weight loss, night sweats, hemoptysis (coughing blood)

Organisms Causing Typical Pneumonia

• Streptococcus pneumoniae: most common cause; can cause severe, lobar pneumonia.

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

• Klebsiella pneumoniae: often in healthcare settings; can cause severe, necrotizing pneumonia.

Chapter 18: Nervous System Infections

Blood-Brain Barrier and Molecular Transport

• The blood-brain barrier (BBB) is a selective barrier that protects the brain from pathogens and toxins.

• Only certain molecules (e.g., glucose, some amino acids) can cross via specific transport mechanisms.

• Most pathogens cannot cross the BBB unless it is compromised.

Viral vs. Bacterial Meningitis

Feature	Viral Meningitis	Bacterial Meningitis
Severity	Usually mild	Often severe, life-threatening
Common Causes	Enteroviruses	Neisseria meningitidis, Streptococcus pneumoniae, Haemophilus influenzae
Treatment	Supportive care	Antibiotics

Polio: Signs and Symptoms

• Caused by poliovirus.

• Symptoms: fever, sore throat, headache, muscle weakness, paralysis (in severe cases).

Bacterial Meningitis: Causative Agents

• Neisseria meningitidis: causes meningococcal meningitis; rapid onset, can cause outbreaks.

• Streptococcus pneumoniae: most common in adults.

• Haemophilus influenzae: previously common in children, now reduced by vaccination.

Leprosy: Lepromatous vs. Tuberculoid Forms

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

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

Tetanospasmin vs. Botulinum Toxin

Toxin	Source	Effect	Transmission
Tetanospasmin	Clostridium tetani	Muscle spasms, rigidity (lockjaw)	Entry via wounds
Botulinum Toxin	Clostridium botulinum	Flaccid paralysis	Ingestion of contaminated food

Arboviruses and Nervous System Infections

• Arboviruses (e.g., West Nile virus) are transmitted by arthropods (mosquitoes, ticks).

• Can cause encephalitis and meningitis.

Toxoplasmosis

• Caused by Toxoplasma gondii, a protozoan parasite.

• Transmitted via undercooked meat or cat feces.

• Can cause severe disease in immunocompromised individuals and congenital infections.

Additional info: These notes are based on the exam study guide and blueprint, with expanded academic context for each topic to ensure completeness and clarity for exam preparation.