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Questions and Answers

What defines prokaryotic microorganisms?

  • Presence of membrane-bound organelles
  • Lack of a nucleus (correct)
  • Presence of a protein coat
  • Complex cellular structure

    • What is a prion?

  • A microscopic plant pathogen
  • A pathogen with a protein coat
  • A noncellular infectious agent composed of misfolded proteins (correct)
  • A type of eukaryotic cell

    • Which organism is known to cause Lyme disease?

  • Treponema pallidum
  • Borrelia burgdorferi (correct)
  • Leptospira interrogans
  • Campylobacter spp

    • Which of the following are characteristics of viruses?

    <p>Consist of nucleic acid and a protein coat (C)</p> Signup and view all the answers

    What do viroids primarily affect?

    <p>Plant cells (C)</p> Signup and view all the answers

    Which of the following describes the bacteria known as Campylobacter spp?

    <p>Aerobic, slightly curved, or helical Gram-negative bacteria (A)</p> Signup and view all the answers

    Which classification of microorganisms are characterized by the presence of a nucleus?

    <p>Eukaryotes (A)</p> Signup and view all the answers

    What distinguishes the methods of reproduction in microorganisms?

    <p>Binary fission, mitosis, or meiosis (C)</p> Signup and view all the answers

    What is a key factor in the transition of normal flora to opportunistic pathogens?

    <p>Imbalance in the immune system (D)</p> Signup and view all the answers

    Which of the following is considered an endogenous source of infection?

    <p>Normal flora entering wounds (D)</p> Signup and view all the answers

    What stage follows contamination in the process of infection?

    <p>Infection (D)</p> Signup and view all the answers

    Which type of pathogen frequently uses the respiratory tract as a portal of entry?

    <p>Viruses (D)</p> Signup and view all the answers

    What is a common effect of a compromised immune system?

    <p>Higher susceptibility to infections (D)</p> Signup and view all the answers

    Through which portal do enteric bacteria typically enter the body?

    <p>Gastrointestinal tract (B)</p> Signup and view all the answers

    Which factor is least likely to contribute to the opportunistic nature of pathogens?

    <p>Maintaining a balanced diet (B)</p> Signup and view all the answers

    What type of microorganisms can act as opportunistic pathogens when normal flora balance is disrupted?

    <p>Bacteria, viruses, and fungi (C)</p> Signup and view all the answers

    What type of host do Rickettsiae require for replication?

    <p>Both vertebrate and arthropod hosts (C)</p> Signup and view all the answers

    Which of the following is a characteristic of Gram-Positive Cocci?

    <p>They can be both aerobic and anaerobic (D)</p> Signup and view all the answers

    Which of the following bacteria is known for causing food poisoning?

    <p>Clostridium perfringens (D)</p> Signup and view all the answers

    Which type of virus carries RNA as genetic material and does not replicate using DNA?

    <p>RNA virus (A)</p> Signup and view all the answers

    What is a common mechanism of host cell damage caused by viral infections?

    <p>Increased membrane permeability (A)</p> Signup and view all the answers

    Which of the following describes an abortive viral infection?

    <p>Infection without viral production (D)</p> Signup and view all the answers

    Which of the following statements is true regarding mycobacteria?

    <p>They can colonize in the host without symptoms (A)</p> Signup and view all the answers

    What is the main role of Lactobacilli in food production?

    <p>Convert lactose and other sugars to lactic acid (B)</p> Signup and view all the answers

    Which of the following does NOT describe Chlamydiae?

    <p>Can infect invertebrates (D)</p> Signup and view all the answers

    What distinguishes reverse transcribing viruses from other types of viruses?

    <p>They replicate via a DNA intermediate (D)</p> Signup and view all the answers

    What term describes the degree of pathogenicity or disease-provoking power of a microbe?

    <p>Virulence (A)</p> Signup and view all the answers

    Which of the following is NOT a mechanism by which microbes evade host defenses?

    <p>Interfering with metabolic processes (D)</p> Signup and view all the answers

    What type of immunity does NOT result in apparent symptoms but can be carried for long periods?

    <p>Subclinical infection (D)</p> Signup and view all the answers

    Which of the following best describes a systemic infection?

    <p>Spreads to multiple sites and tissue fluids (B)</p> Signup and view all the answers

    Which type of toxin is characterized as being less potent and less specific than its counterpart?

    <p>Endotoxin (D)</p> Signup and view all the answers

    What is the main function of adhesins in the infection process?

    <p>To facilitate the binding of bacteria to host cells (B)</p> Signup and view all the answers

    Which pattern of infection is defined as having several infectious agents establish themselves at the same site?

    <p>Mixed infection (B)</p> Signup and view all the answers

    What is the term used to describe the permanent place where causative agents of infection reside?

    <p>Reservoir of infection (C)</p> Signup and view all the answers

    Which type of infection has rapid onset and quickly resolves?

    <p>Acute infection (A)</p> Signup and view all the answers

    Where do pathogens typically colonize in the human body?

    <p>Tissues exposed to the external environment (B)</p> Signup and view all the answers

    Which organization serves as the central source of epidemiological information in the United States?

    <p>Centers for Disease Control and Prevention (C)</p> Signup and view all the answers

    Which category of disease occurs with greater frequency than usual in a given population?

    <p>Epidemic disease (A)</p> Signup and view all the answers

    What is typically the portal of entry for microbes in vaginal yeast infections?

    <p>Urogenital tract (D)</p> Signup and view all the answers

    Which of the following describes a phenomenon where pathogens are directly introduced to subcutaneous tissue?

    <p>Parenteral route (B)</p> Signup and view all the answers

    Which of the following viruses is known to cause smallpox?

    <p>Poxviruses (A)</p> Signup and view all the answers

    What type of virus is primarily responsible for causing respiratory and enteric diseases, including SARS?

    <p>Coronaviruses (B)</p> Signup and view all the answers

    Which of the following groups includes the causative agent of hepatitis B?

    <p>Hepadnaviruses (A)</p> Signup and view all the answers

    What is the smallest known DNA virus that causes disease in humans?

    <p>Parvovirus B19 (D)</p> Signup and view all the answers

    What type of organism is typically characterized as eukaryotic, unicellular, and lacking a cell wall?

    <p>Protozoans (B)</p> Signup and view all the answers

    Which of the following is a characteristic of nematodes?

    <p>Can be seen with the naked eye (D)</p> Signup and view all the answers

    In which type of symbiotic relationship do both organisms benefit from the interaction?

    <p>Mutualism (C)</p> Signup and view all the answers

    Which fungi-associated structure plays a major role in symbiosis with plant roots?

    <p>Mycorrhizae (C)</p> Signup and view all the answers

    Which of the following viruses is highly pathogenic and belongs to the Paramyxovirus group?

    <p>Nipah virus (D)</p> Signup and view all the answers

    What describes a parasite that causes disease?

    <p>Pathogen (A)</p> Signup and view all the answers

    How do many protozoans ensure survival during unfavorable environmental conditions?

    <p>By entering a dormant cyst stage (A)</p> Signup and view all the answers

    Which of the following is a typical characteristic of resident flora in humans?

    <p>Remain part of the flora throughout a person's life (A)</p> Signup and view all the answers

    What role do fungi commonly play in the ecosystem?

    <p>Decomposers (A)</p> Signup and view all the answers

    Which of the following statements about transient flora is true?

    <p>They exist in the body for brief periods. (C)</p> Signup and view all the answers

    What are nonliving reservoirs that can harbor pathogens?

    <p>Soil, water, and food (D)</p> Signup and view all the answers

    What term is used to describe diseases primarily occurring in animals that can be transmitted to humans?

    <p>Zoonoses (A)</p> Signup and view all the answers

    Which of the following is a mode of transmission for infectious diseases?

    <p>Vector transmission (C)</p> Signup and view all the answers

    What is the most effective form of droplet transmission?

    <p>Sneezing (A)</p> Signup and view all the answers

    What is a biological vector?

    <p>An organism that harbors a pathogen and transmits it (D)</p> Signup and view all the answers

    What are healthcare-associated infections primarily caused by?

    <p>A combination of endogenous and exogenous factors (A)</p> Signup and view all the answers

    How can antimicrobial resistance in healthcare settings manifest?

    <p>Resistance in over 70% of bacteria to common drugs (B)</p> Signup and view all the answers

    What is a key feature of nosocomial infections?

    <p>They are acquired in hospital settings (B)</p> Signup and view all the answers

    Which of the following is NOT a common route for zoonotic transmission?

    <p>Transmission from infected plants (D)</p> Signup and view all the answers

    What type of infection is caused by the patient's own microbial flora becoming pathogenic?

    <p>Endogenous infections (B)</p> Signup and view all the answers

    Which of the following is a characteristic of indirect contact transmission?

    <p>It involves transmission via fomite (D)</p> Signup and view all the answers

    Which mode of transmission includes pathogens traveling more than 1 meter?

    <p>Airborne transmission (A)</p> Signup and view all the answers

    What is one primary prevention method for infectious diseases?

    <p>Widespread vaccination (A)</p> Signup and view all the answers

    What is a significant challenge posed by healthcare-associated infections?

    <p>Patients have compromised immune systems (A)</p> Signup and view all the answers

    Study Notes

    Microbiology

    • The study of microorganisms, including their visualization, identification, and function.
    • Originated with the invention of the microscope.
    • Microorganisms can be classified as prokaryotes (lacking a membrane-bound nucleus) or eukaryotes (with membrane-bound organelles).
    • Prokaryotes include archaea and bacteria.
    • Eukaryotes include algae, fungi, and protozoans.

    Shared Properties of Microorganisms

    • Reproduce through cell division, including binary fission, mitosis, or meiosis.
    • Contain DNA and RNA for protein synthesis.
    • Possess plasma membranes.

    Viruses

    • Noncellular, submicroscopic particles consisting of nucleic acid surrounded by a protein coat.
    • Obligate intracellular parasites that infect both eukaryotes and prokaryotes.
    • Can be classified based on their genome type: dsDNA, ssDNA, dsRNA, or ssRNA.

    Prions

    • Not cellular or viral, lacking nucleic acids.
    • Misfolded proteins that act as infectious agents, leading to transmissible spongiform encephalopathies (e.g., mad cow disease, kuru).

    Viroids

    • Plant pathogens lacking a protein coat.

    Microbial Ecology

    • Often involves biofilms, which are communities of microorganisms attached to a surface.
    • Microorganisms can interact in various ways, including:
      • Mutualism: Both organisms benefit.
      • Commensalism: One organism benefits, and the other is unaffected.
      • Synergism: Both organisms benefit from the interaction but can survive independently.
      • Parasitism: One organism benefits at the expense of the other.
      • Amensalism: One organism inhibits the growth of another without being affected itself.

    Bacteria

    • A diverse group of prokaryotes with various shapes, sizes, and metabolic capabilities.
    • Classified based on their morphology, staining properties (Gram-positive or Gram-negative), and oxygen requirements (aerobic, anaerobic, or facultative anaerobic).

    Spirochetes

    • Helical, motile bacteria with twisting motions due to axial fibrils.
    • Found in aquatic environments and associated with human or animal hosts.
    • Important pathogens include:
      • Treponema pallidum (syphilis)
      • Borrelia burgdorferi (Lyme disease)
      • Leptospira interrogans (Leptospirosis)

    Aerobic/Microaerophilic Helical Vibrioid Gram-Negative Bacteria

    • Slightly curved or have multiple helical turns.
    • Motile with flagella.
    • Live in aquatic environments.
    • Medically important examples include:
      • Campylobacter spp.
      • Helicobacter pylori

    Gram-Negative Aerobic Rods and Cocci

    • Diverse group, widely distributed in nature.
    • Many are human and animal pathogens.
    • Medically important examples include:
      • Legionella pneumophila
      • Neisseria gonorrhoeae
      • Neisseria meningitidis
      • Bordetella pertussis
      • Francisella tularensis
      • Pseudomonas aeruginosa

    Facultative Anaerobic Gram-Negative Rods

    • Large group with simple nutritional requirements.
    • Found in soil, water, and the intestinal tract of animals and humans.
    • E. coli is a key organism in molecular biology.
    • Most strains are harmless, but some can cause gastroenteritis, UTIs, and hemorrhagic gastritis.

    Rickettsias and Chlamydias

    • Very small, gram-negative bacteria that require a host for replication.
    • Generally rod-shaped but can be coccoidal.
    • Often cause disease.
    • Rickettsiae need a vertebrate and an arthropod host (e.g., Rickettsia rickettsii causes Rocky Mountain spotted fever transmitted by ticks).
    • Chlamydias do not infect invertebrates (e.g., Chlamydia trachomatis causes urogenital infections).

    Gram-Positive Cocci

    • Include aerobic and anaerobic bacteria.
    • Range from harmless to very virulent.
    • Includes Micrococcus, Staphylococcus, Streptococcus, and Peptococcus.
    • Medically important examples include:
      • Staphylococcus aureus
      • Streptococcus pyogenes
      • Streptococcus pneumoniae
      • Peptostreptococcus

    Endospore-Forming Gram-Positive Rods and Cocci

    • Include Bacillus and Clostridium.
    • Important in medicine and the food industry.
    • Spores are resistant to heat and disinfectants.
    • Widespread in the soil.
    • Clostridium perfringens is found in decaying matter, marine sediment, and the intestinal tract of humans and other animals.
    • Bacillus species are either obligate aerobes or facultative anaerobes.
    • Clostridium species are mainly obligate anaerobes.
    • Medically important examples include:
      • Bacillus anthracis
      • Bacillus cereus
      • Clostridium botulinum
      • Clostridium difficile
      • Clostridium perfringens
      • Clostridium tetani

    Regular Nonsporulating Gram-Positive Rods

    • Obligate or facultative anaerobes.
    • Complex nutritional requirements.
    • Includes Carnobacterium, Lactobacillus, and Listeria.
    • Lactobacilli convert sugars to lactic acid, used in the production of yogurt, cheese, sauerkraut, and pickles.
    • Listeria monocytogenes causes listeriosis.

    Irregular Nonsporing Gram-Positive Rods

    • Unusual shape.
    • Mostly facultative anaerobes, few obligate aerobes.
    • Medically important examples include:
      • Actinomyces (opportunistic)
      • Corynebacterium diphtheria (diphtheria)
      • Propionibacterium acnes (acne)
      • Actinomyces israelii (periodontal disease, lung infections)

    Mycobacteria

    • Gram-positive, aerobic, acid-fast rods.
    • Found in water, soil, and food sources.
    • Some are obligate intracellular parasites in humans and animals.
    • Difficult to treat infections.
    • Naturally resistant to many antibiotics.
    • Medically important examples include:
      • Mycobacterium tuberculosis
      • Mycobacterium leprae

    Viruses

    • Microscopic particles that infect cells or other organisms.
    • Contain either DNA or RNA but cannot reproduce on their own.
    • Obligate intracellular parasites.
    • Bacteriophages are viruses that infect bacteria.

    Viral Infections

    • Abortive: No viral production.
    • Lytic or cytocidal: Kills the host cell.
    • Persistent: Chronic (not lytic but productive) or latent (limited synthesis, virus remains in asymptomatic host).
    • Slow infections: Prolonged incubation, damage might take years, followed by disease.
    • Transforming infections: Viral nucleic acid may remain indefinitely without virus production, possible oncogenic changes.

    Major Groups of Viruses in Vertebrates

    • Cause disease after breaking protective barriers and gaining access to underlying tissues.
    • Most viruses are specific to a particular cell or tissue type.
    • Viral genomes consist of either DNA or RNA.

    DNA Viruses

    • Adenoviruses: Cause respiratory illness, gastroenteritis, conjunctivitis, cystitis, and rashes.
    • Hepadnaviruses: Cause hepatitis in humans and animals (e.g., Hepatitis B).
    • Herpesviruses: Include Herpes simplex 1 and 2, Varicella-zoster.
    • Papillomaviruses and polyomaviruses: Cause warts and possibly cervical carcinomas.
    • Parvoviruses: The smallest DNA viruses, B19 causes human disease, others infect animals.
    • Poxviruses: The largest viruses, cause smallpox.

    RNA Viruses

    • Bunyaviridae: Arthropod-borne viruses.
    • Coronaviruses: Cause respiratory and enteric disease, including SARS-CoV-2.
    • Hepatitis viruses: Cause hepatitis (A through E) and can lead to cirrhosis and hepatocellular carcinomas.
    • Orthomyxoviruses: Include influenza A, B, and C viruses.
    • Paramyxoviruses: Include Morbillivirus, Paramyxovirus (highly pathogenic), Pneumovirus, Nipah and Hendra viruses (zoonosis-causing).
    • Picornaviruses: Important pathogens, include Enterovirus, Rhinovirus, Hepatovirus, Aphthovirus, Parechovirus, Erbovirus, Kobuvirus, Teschovirus.
    • Rhabdoviruses: Infect plants, insects, fish, birds, mammals, including humans (e.g., rabies virus).
    • Reoviruses: Not associated with a specific disease but include Rotavirus, which causes gastroenteritis in children.
    • Retroviruses: Include Oncovirinae, Lentivirinae, Spumavirinae (e.g., HIV).
    • Togaviruses: Include Alphavirus (infectious arthritis, encephalitis, fever) and Rubivirus (rubella virus).
    • Flaviviruses: Cause yellow fever, encephalitis, dengue fever, hepatitis C, and West Nile virus.

    Eukaryotic Microorganisms

    Fungi

    • The study of fungi is called mycology.
    • Few fungi are pathogenic and virulent.
    • Immune system usually fights fungal invasion.
    • Have important symbiotic relationships with other organisms.
    • Play a major role in decomposition.
    • Mycorrhizae are fungi that live on plant roots.
    • Fungal colonies are vegetative and appear as yeast, molds, or fleshy fungi.
    • Have cell walls composed of chitin.

    Yeast

    • Unicellular fungi that reproduce by budding.

    Molds

    • Multicellular fungi that grow as filamentous hyphae.

    Protozoans

    • Eukaryotes, unicellular, and lack a cell wall.
    • Most are free-living, but some are parasites of humans and other animals.
    • Diverse group of microbes, most are motile by cilia, flagella, or pseudopodia.
    • Require a moist environment.
    • Most live in ponds, streams, lakes, and oceans.
    • Most are chemoheterotrophs and obtain nutrients from bacteria, decaying organic matter, other protozoans, or host tissue.
    • Many enter a dormant stage (cyst) when the environment becomes unfavorable, which can be distributed by air.

    Helminths

    • Multicellular parasitic worms that produce microscopic infective and diagnostic stages in their life cycle.
    • Often found in blood, feces, and urine.
    • Spend much of their life cycle in a mammalian host.
    • Most are either flatworms (platyhelminths) or roundworms (nematodes).
    • Adult animals are typically large enough to be seen with the naked eye.
    • Eggs and larvae are microscopic.

    Platyhelminths (Flatworms)

    • Trematodes (lung fluke, liver fluke, blood fluke), named by their host tissue.
    • Cestodes or tapeworms, intestinal parasites.

    Nematodes (Roundworms)

    • Enterobius vermicularis (pinworm), spends its life in the human host, eggs transmitted by fomites.
    • Ascaris lumbricoides (human parasite without an intermediate host).
    • Necator americanus and Ancylostoma duodenale (hookworm), found in the small intestine of humans.

    Symbiosis

    • A close relationship between two different types of organisms in a community.

    Mutualism

    • Both members benefit from the interaction.

    Commensalism

    • One organism benefits, and the other is neither harmed nor helped.

    Parasitism

    • One organism benefits while the other is harmed.
    • Pathogen: A parasite that causes disease.

    Amensalism

    • One organism can hamper or prevent the growth/survival of another without being affected by the other organism.

    Normal Flora

    • Microorganisms that establish residency in mucous membranes open to the environment.
    • Resident flora remain part of the normal flora throughout life.
    • Transient flora are found in the same locations as resident flora, but only remain for a short period.

    Opportunistic Pathogens

    • Pathogens are microorganisms capable of causing disease.
    • Opportunistic pathogens do not cause disease in their normal habitat in a healthy person.
    • Causes of opportunistic infections include a compromised immune system, changes in normal flora, and entrance of normal flora into areas where it is not normally present.

    Stages of Infection

    • Contamination: Presence of microbes in or on the body.
    • Infection: Presence and growth of a microorganism in the body (excluding normal flora).
    • The microorganism must gain entry into the host and its tissues.
    • Not all infections cause disease.

    Portals of Entry

    • Sites where pathogens enter the body.
    • Source of infection can be exogenous (from outside the body) or endogenous (organism is already in the body).
    • Majority of pathogens have preferred portals of entry.

    Skin

    • A thick layer of keratinized dead cells.
    • Pathogens can enter through natural openings or damaged skin.

    Mucous Membranes

    • Gastrointestinal tract: Portal of entry for pathogens present in food, liquids, and ingested substances.
    • Respiratory tract: The most frequent portal of entry for pathogens in air, dust, moisture, and respiratory droplets.
    • Urogenital tract: Pathogens usually contracted by sexual contact.

    Additional Notes

    • E. coli is often referred to as the ‘workhouse’ of molecular biology, due to its use in numerous studies and applications.
    • Clostridium difficile is commonly associated with antibiotic-associated diarrhea and colitis.
    • Bacillus anthracis is associated with anthrax, which can be fatal if untreated.
    • Corynebacterium diphtheriae causes diphtheria, a potentially severe illness.

    Vaginal Yeast Infections

    • Caused by overgrowth of Candida albicans
    • Opportunistic infection

    Barriers of the Body Against Infectious Agents

    • Conjunctiva: Usually a good barrier, but some bacteria can attach easily.
    • Placenta: Usually effective in preventing microbes, however, some can cross and infect the embryo or fetus, leading to spontaneous abortions, birth defects, or premature births.

    Parenteral Route

    • Not a true portal of entry, more a bypassing of portals of entry.
    • Introduces pathogens directly into subcutaneous tissue.
    • Examples: Punctures by nail, thorn, contaminated needles, cuts, bites, stab wounds, deep abrasions, surgery.

    Virulence and Pathogenicity

    • Virulence: The degree of pathogenicity or disease-provoking power of a specific microbe.
    • Virulence factors contribute to virulence.
    • Pathogenicity: The ability of a microbe to cause disease.
    • Factors influencing pathogenicity include:
      • Number of microorganisms
      • Portal of entry
      • Host defense mechanisms
      • Intrinsic characteristics of the organism
      • Virulence factors

    Adhesion

    • First and most crucial step in infection.
    • Without adhesion, the organism will be removed by natural mechanisms like ciliary motion, sneezing, coughing, swallowing, urine flow, tears, and intestinal peristalsis.
    • Bacteria must bind to host cells using pili, fimbriae, or specific membrane receptor sites.
    • Adhesion can be specific or nonspecific.
      • Specific: Involves a lock-and-key interaction between molecules on pathogen and host cells.
      • Nonspecific: Based on electrostatic forces and atomic & molecular vibrations.

    Colonization and Invasion

    • Human pathogens usually colonize tissues that are in contact with the external environment:
      • Urogenital tract
      • Digestive tract
      • Respiratory tract
      • Conjunctiva
    • Invasion: May be facilitated by extracellular substances that disrupt host cell membranes, breaking down the body's primary and secondary barriers.
    • Invasins are substances produced by pathogens that help them grow and spread.

    Evasion of Host Defense

    • Pathogens have strategies to evade host defenses:
      • Capsules: Prevent phagocytosis by immune cells.
      • Production of proteins that bind to host antibodies, disguising the pathogen from the immune system.
      • Mutation of surface antigens, changing the pathogen's appearance to evade recognition by the immune system.
      • Avoiding contact with phagocytes.
      • Inhibiting phagocytic engulfment.
      • Surviving inside phagocytes.
      • Production of products that kill or damage phagocytes before or after ingestion.

    Toxins

    • Toxigenic: Organism produces toxins.
    • Toxins are the underlying mechanism by which microorganisms cause disease.
    • Bacterial toxins can be endotoxins or exotoxins.
      • Endotoxins: Found within the bacterial cell wall (lipopolysaccharides).
      • Exotoxins: Secreted by bacteria (proteins).

    Exotoxins

    • Released by bacteria during the exponential growth phase.
    • Can act at sites different from the site of infection.
    • Often species specific and associated with a particular disease.

    Endotoxins

    • Lipopolysaccharides of Gram-negative bacterial cell walls.
    • Released during lysis (breakdown) of the bacteria, initiated by host defenses or antibiotics.
    • Less potent and less specific than exotoxins.
    • Can act on sites remote from the original site of infection.

    Portal of Exit

    • The site where the pathogen leaves the infected person.
    • Often the same as the portal of entry.
    • Pathogens can also leave the host through excretion or secretion.

    Etiology of Infectious Disease

    • The study of the cause of disease when an infectious agent causes pathological changes and interferes with normal body functions.

    Patterns of Infection

    • Local infections: Organism enters the body and remains confined to a specific tissue.
    • Focal infections: Pathogen spreads from a local infection to other tissues.
    • Systemic infections: Infection spreads to several sites and tissue fluids, usually by the way of the circulatory system.
      • Septicemia
      • Bacteremia
      • Toxemia
      • Viremia
    • Mixed infections: Several infectious agents concurrently establish themselves at the same site.

    Patterns of Infection (Continued)

    • Acute infections: Appear rapidly with severe symptoms and vanish quickly.
    • Chronic infections: Usually less severe symptoms, but they persist for long periods.
    • Primary infections: The initial infection.
    • Secondary infections: Follows a primary infection, typically caused by a different microbe.
    • Subclinical infections: Don't cause any apparent symptoms.
    • Carriers: Infected individuals without symptoms, who can infect others.

    Epidemiology and Public Health

    • Epidemiology: The study of the distribution and cause of disease in populations.
    • Serves as the foundation for public health interventions and preventive medicine.
    • Investigates:
      • Number of people affected
      • Location of the disease
      • Outcome of the disease (recovery, death, disability)

    Major Public Health Organizations

    • Public Health Agency of Canada: Central source for epidemiological information in Canada.
    • Centers for Disease Control and Prevention (CDC): Central source of epidemiological information in the United States.

    Morbidity and Mortality Weekly Report (MMWR)

    • Published by the CDC.
    • Contains data on morbidity (incidence of specific notifiable diseases) and mortality.

    Diseases in the Population

    • Prevalence: The total number of existing cases in the entire population.
    • Incidence: The number of new cases over a certain period compared to the general healthy population.

    Disease Categories

    • Endemic diseases: Repeatedly present in a given population or geographical area.
    • Sporadic diseases: Break out only occasionally.
    • Epidemic diseases: Occur with greater frequency than usual in a population of a given area.
    • Pandemic diseases: Worldwide epidemics.

    Reservoirs

    • For an infection to continue, its causative agent must have a permanent place to reside.
    • Reservoirs of infection maintain pathogens and are sources of infection:
      • Nonliving reservoirs: Soil, water, food.
      • Animal reservoirs: Zoonoses - diseases that occur primarily in animals and can be transmitted to humans.
      • Human carriers: Main reservoir for human infectious agents; infected individuals without symptoms.

    Routes of Zoonoses

    • Direct contact with infected animals.
    • Contact with animal waste.
    • Contaminated food or water.
    • Dust from contaminated hides, fur, or feathers.
    • Consuming infected animal products.
    • Insect vectors.

    Modes of Transmission

    • For infectious diseases to spread, they must move from a reservoir or portal of exit to a portal of entry of another host.
      • Contact transmission
      • Vehicle transmission
      • Vector transmission

    Contact Transmission

    • Direct contact: Direct physical contact between hosts without an intermediate object. - Examples: Respiratory tract infections, staphylococcal infections, measles, scarlet fever, sexually transmitted diseases.
    • Indirect contact: Pathogen is transmitted by a fomite (nonliving object). - Examples: Tissues, handkerchiefs, towels, bedding, toys, clothes, diapers, eating utensils, drinking cups, medical equipment.
    • Droplet transmission: Via respiratory droplets released by exhaling, laughing, coughing, or sneezing.

    Vehicle Transmission

    • Airborne transmission: Via droplet nuclei or aerosols.
      • Droplet nuclei: Droplets of mucous.
      • Other aerosols: Dust.
      • Airborne transmission requires travel of more than 1 meter.
    • Bodily fluid transmission: Especially relevant for healthcare workers. - Precautions are necessary when handling fluids that may be contaminated with pathogens. - Examples: Blood, urine, saliva, and other bodily fluids.
    • Waterborne transmission: Through untreated or poorly treated sewage. - Examples: Giardiasis, amebic dysentery, cholera, water-borne shigellosis, leptospirosis.
    • Foodborne transmission: Incompletely cooked, poorly processed, or unsanitary foods. - Contamination by normal flora, zoonotic pathogens, or parasitic worms.

    Vector Transmission

    • Animals, especially arthropods, serving as vectors.
    • Biological vectors: Transmit pathogens and also serve as a host for a part of the pathogen's life cycle. - Example: Mosquitoes, ticks, lice, fleas, blood-sucking flies or bugs, mites.
    • Mechanical vectors: Passively carry agents to a new host. - Example: Flies.

    Vaccinations

    • Most effective method of preventing infectious diseases.
    • Public health agencies provide information on vaccine-preventable diseases.
    • Examples: Health Canada, CDC's Global Immunization Division (GID).
    • Vaccinations have eradicated smallpox and polio.

    Healthcare-Associated (Nosocomial) Infections

    • Acquired as a result of treatments in a hospital or hospital-like setting.
    • Secondary to the patient’s original condition.
    • Among the top 10 leading causes of death in the United States.
    • Incidence of MRSA and VRE bloodstream infections in Canadian hospitals has increased significantly.

    Types of Nosocomial Infections

    • Exogenous: Caused by pathogens in the healthcare environment.
    • Endogenous: Caused by microbes in the normal flora of the patient, becoming pathogenic due to weakened immune systems, antimicrobial drugs, or overgrowth.
    • Iatrogenic: Result from medical procedures such as the use of catheters, invasive diagnostic procedures, and surgery.

    Transmission of HAIs

    • Direct contact transmission: From hospital staff to patient, visitors, and patient to patient.
    • Indirect contact transmission: Through fomites.
    • Airborne transmission: Through ventilation systems.

    Antimicrobial Resistance in Healthcare Settings

    • Drug-resistant pathogens are a growing threat.
    • More than 70% of bacteria causing infections are resistant to at least one commonly used drug.

    Control and Prevention of HAIs

    • Safety programs, policies, and procedures: Implemented by healthcare facilities to prevent transmission of pathogens.
    • Blood-borne pathogen training.
    • Proper handwashing and good housekeeping.
    • Infection control committees: Established in accredited hospitals.

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