INFECTIOUS DISEASES

Infectious diseases

Diseases that result from interactions between microorganisms and hosts

Microorganisms

Organisms that interact with hosts and can cause infectious diseases

Disease

Result of microbial factors interacting with host factors, leading to tissue injury and clinical manifestations

Microbial factors

Factors from the microorganism that contribute to disease development

Host factors

Factors from the host that influence development and severity of disease

Tissue injury

Damage resulting from microbial and host factors during infection

Clinical manifestations

Signs and symptoms resulting from tissue injury caused by infection

Infection

Entry and multiplication of a microorganism within a host

Infectious dose

Amount of microorganism required to establish infection

Route of entry

Pathway through which a microorganism enters the host

Virulence

Degree to which a microorganism can cause disease

Microbial tropism

Preference of a microorganism for particular host cells or tissues

Host immune status

Condition of the host's immune defenses that influences susceptibility to infection

Genetic susceptibility

Host genetic factors that influence susceptibility to infection

Adherence

Attachment of microorganisms to host cells

Colonization

Establishment and multiplication of microorganisms at a host site

Invasion

Penetration of microorganisms into host tissues

Evasion of host defenses

Ability of microorganisms to avoid or overcome host immune defenses

Replication

Multiplication of microorganisms within the host

Tissue injury

Result of microbial replication and host

Innate immunity

Immediate, nonspecific defense against microorganisms

Adaptive immunity

Specific immune response that develops against microorganisms

Inflammation

Host response that helps eliminate microorganisms and initiate tissue repair

Tissue repair

Process that restores damaged tissue after infection and inflammation

Respiratory tract

Major portal of entry for infectious microorganisms

Gastrointestinal tract

Major portal of entry for infectious microorganisms

Genitourinary tract

Major portal of entry for infectious microorganisms

Skin

Major portal of entry for infectious microorganisms

Mucous membranes

Major portal of entry for infectious microorganisms

Blood

Portal of entry for infectious microorganisms

Placenta

Portal through which some infections can reach the fetus

Respiratory droplets/aerosols

Mode of transmission through respiratory particles

Fecal

oral transmission

Direct contact

Transmission through physical contact with an infected host or contaminated source

Sexual transmission

Transmission through sexual contact

Arthropod vectors

Organisms such as insects or ticks that transmit infectious microorganisms

Contaminated food/water

Sources of infection through ingestion

Vertical transmission

Transmission of infection from mother to fetus or newborn

Route of entry

Often determines the initial organs affected and the type of disease

Direct cellular damage

Microbial injury mechanism in which microorganisms directly damage host cells

Toxins

Microbial products that can injure host tissues

Enzymes

Microbial products that contribute to tissue injury

Nutrient depletion

Microbial injury mechanism in which microorganisms consume nutrients needed by the host

Induction of inflammation

Microbial injury mechanism in which microorganisms trigger inflammatory responses

Immune

mediated tissue injury

Alteration of cellular growth

Microbial injury mechanism that changes normal cellular proliferation or growth

Immune response

Can cause as much or more tissue damage than the microorganism itself

Virulence factors

Microbial characteristics that allow microorganisms to cause disease

Adherence

Function of virulence factors that allows microorganisms to attach to host cells

Invasion

Function of virulence factors that allows microorganisms to penetrate host tissues

Phagocytosis evasion

Function of virulence factors that allows microorganisms to avoid being engulfed by phagocytes

Complement resistance

Function of virulence factors that allows microorganisms to resist complement

Intracellular survival

Ability of microorganisms to survive inside host cells

Nutrient acquisition

Ability of microorganisms to obtain nutrients needed for survival and replication

Toxin production

Ability of microorganisms to produce substances that cause tissue injury

Capsules

Virulence factor that inhibits phagocytosis

Inhibition of phagocytosis

Function of bacterial capsules

Adhesins

Virulence factors that promote attachment to host cells

Attachment to host cells

Function of adhesins

Protein A

Virulence factor that interferes with antibody function

Interference with antibody function

Function of Protein A

Coagulase

Virulence factor that promotes fibrin formation

Fibrin formation

Function of coagulase

Endotoxin

Virulence factor that triggers systemic inflammation

Skin and mucosal barriers

Innate defenses against microorganisms

Antimicrobial peptides

Innate defenses that inhibit or kill microorganisms

Complement

Innate immune defense against microorganisms

Neutrophils

Innate immune cells that respond rapidly to infection

Macrophages

Innate immune cells that engulf microorganisms and contribute to immune responses

Natural killer (NK) cells

Innate immune cells that kill infected or abnormal cells

Pattern recognition receptors (PRRs)

Receptors that detect pathogen

Pathogen

associated molecular patterns (PAMPs)

Humoral immunity

Immune response mediated mainly by B cells and antibodies

B cells

Lymphocytes that produce antibodies

Antibodies

Products of B cells important in defense against extracellular bacteria, toxins, and some viruses

Extracellular bacteria

Organisms against which humoral immunity is particularly important

T cells

Lymphocytes responsible for cell

Cell

mediated immunity

Macrophage activation

Function of T cells important against intracellular organisms

Cytotoxicity

T

Intracellular organisms

Organisms against which cell

Viruses

Organisms against which cell

Mycobacteria

Organisms against which cell

Certain fungi

Organisms against which cell

Suppurative pattern

Tissue response characterized by neutrophils, pus, and abscess formation

Neutrophils, pus, and abscess formation

Tissue response pattern known as suppurative

Mononuclear pattern

Tissue response characterized by lymphocytes and macrophages

Lymphocytes and macrophages

Tissue response pattern known as mononuclear

Granulomatous pattern

Tissue response characterized by activated macrophages and giant cells

Activated macrophages and giant cells

Tissue response pattern known as granulomatous

Cytopathic pattern

Tissue response characterized by cellular enlargement and inclusions

Cellular enlargement and inclusions

Tissue response pattern known as cytopathic

Necrotizing pattern

Tissue response characterized by extensive tissue destruction

Extensive tissue destruction

Tissue response pattern known as necrotizing

Suppurative inflammation

Inflammation characterized by neutrophil accumulation, liquefactive tissue destruction, pus, and abscess formation

Pus

Collection of neutrophils and necrotic material produced during suppurative inflammation

Abscess

Localized collection of pus caused by suppurative inflammation

Staphylococcus

Common bacterial cause of suppurative inflammation

Streptococcus

Common bacterial cause of suppurative inflammation

Pyogenic bacteria

Bacteria that commonly cause pus