Infectious Disease Chapter 2 Quiz

Normal Microbiota versus Pathogens

• The human microbiota consists of all microbes residing on the human body, primarily through commensalism or mutualism.
• Commensalism benefits one organism without affecting the other, while mutualism benefits both.
• Colonization is the ability of microbes to attach and replicate on host surfaces via adhesins.
• Pathogens include bacteria, viruses, fungi, protozoa, or helminths that can cause diseases in humans.
• Pathogenicity refers to a microbe's ability to cause infection or disease, while parasites always harm the host.
• Ectoparasites live on the host's surface (e.g., Trichophyton rubrum), while endoparasites reside within the host (e.g., cause of elephantiasis).

Pathogenesis Terminology

• Infection occurs when pathogens enter a host and grow, often without immediate symptoms.
• Disease is characterized by recognizable symptoms arising from infections.
• Acute infections present rapid onset and resolution of symptoms (e.g., common cold).
• Chronic infections develop gradually with prolonged symptoms (e.g., tuberculosis).
• Latent infections exist when pathogens remain dormant until symptoms re-emerge (e.g., herpes virus).

Pathogen Types

• Primary pathogens are likely to cause disease in healthy hosts (e.g., tuberculosis).
• Opportunistic pathogens are usually harmless but may cause illness in immunocompromised individuals.
• Virulence measures the severity of disease caused by pathogens, often assessed by lethal dose (LD50) and infectious dose (ID50).

Microbial Interaction with Host

• Invasion involves a pathogen entering host cells for survival.
• Invasiveness is the ability of a pathogen to spread rapidly within tissues (e.g., Streptococcus pyogenes).
• Host range indicates the diversity of potential hosts a pathogen can infect.

Disease Definition and Symptoms

• Disease disrupts normal bodily structure/function, identifiable by specific signs and symptoms.
• Signs are observable indicators (e.g., rash, fever), whereas symptoms are felt (e.g., pain, fatigue).
• Syndromes represent a collection of signs and symptoms indicating a specific condition.

Host Immune Response

• Immunopathology refers to host tissue damage resulting from the immune response against pathogens.
• Sequelae are long-term consequences after disease resolution, like heart damage post-streptococcal infection.

Pathogen Strategies

• Attachment is aided by adhesins binding to host cell receptors.
• Immune avoidance strategies can include changing pathogen structure or secreting deceptive signals.
• Nutrient theft, such as siderophores capturing iron, is a strategy utilized by some pathogens.

Stages of Acute Infectious Disease

• Incubation Phase: Initial infection until symptoms appear; host may be contagious.
• Prodromal Phase: Mild non-specific symptoms occur; host can still spread the microbe.
• Illness Phase: Characteristic symptoms manifest; pathogens peak in numbers.
• Decline Phase: Symptoms subside as host defenses prevail; body temperature normalizes.
• Convalescence Phase: Complete recovery and strength restoration.

Epidemiology of Diseases

• Morbidity reflects the illness rate while mortality indicates death rates from diseases.
• Modes of transmission encompass both horizontal (person-to-person) and vertical (parent-to-offspring) transmission routes.
• Direct contact transmission involves direct physical transfer (e.g., touching, kissing).
• Indirect transmission may occur via airborne routes, vehicles (food/water), fomites (inanimate objects), or vectors (e.g., mosquitoes).

Disease Reservoirs and Carriers

• Reservoirs are environments or organisms that support pathogen survival without necessarily showing symptoms.
• Asymptomatic carriers, like Neisseria meningitidis, can transmit diseases without exhibiting symptoms.

Disease Classification

• Endemic disease: Consistently low prevalence within a community, often linked to animal reservoirs.
• Epidemic disease: A sudden increase in disease cases within a community.
• Pandemic disease: An epidemic that spreads globally (e.g., influenza, HIV, COVID-19).
• Zoonotic diseases: Infection cycles involving animal reservoirs that can transmit pathogens to humans.