Chapter 25&26 BIOL3340

Viruses

Small obligate intracellular parasites.

Virion

A virus particle that delivers its RNA or DNA genome into a host cell.

Nucleocapsid

A structure formed by a nucleoprotein and the genome.

Enveloped viruses

Viruses that have a phospholipid bilayer surrounding the nucleocapsid.

Baltimore System of Classification

A system used to classify viruses based on their genome type and replication method.

Morphology

Based upon size and shape, chemical composition, and structure of genome (RNA/DNA, SS, DS) & mode of replication.

Helical

A morphology seen in nucleocapsids where capsid proteins can be wrapped around nucleic acid.

Icosahedral

Nucleocapsids of spherical viruses.

Polyhedral

A type of viral morphology.

Complex

A morphology characterized by a head and tail structure.

Genomic RNA strand

In single stranded (SS) RNA viruses, it is called a sense.

+sense viral RNA

Identical to viral mRNA and is immediately translated into protein by the host cell.

-sense RNA

Complementary to mRNA and must be converted to (+)sense RNA by RNA polymerase before translation.

Viral Multiplication/Replication

The mechanism used depends on viral structure and genome.

7 Steps of Viral Replication

Attachment/Adsorption to host cell, Entry into cell, Uncoating of genome, Replication/Synthesis, Assembly, Maturation, Release.

Infection

A microbe growing and multiplying on or within a host.

Pathogenicity

The ability of a pathogen to cause disease.

Virulence

The degree of harm (pathogenicity) inflicted on the host.

Intracellular pathogens

Pathogens that grow and multiply within host cells.

Extracellular pathogens

Pathogens that grow outside host cells in tissues and fluids.

Facultative intracellular pathogens

Pathogens that reside within the cells of the host or in the environment but can also be grown in pure culture without host cell support.

Obligate intracellular pathogens

Pathogens that only grow when inside host cells.

Incubation period

Period after pathogen entry, before signs and symptoms appear.

Prodromal stage

Onset of signs and symptoms that are not clear enough for diagnosis.

Illness period

Period when the disease is most severe, displaying signs and symptoms.

Convalescence

Period when signs and symptoms begin to disappear, indicating recovery.

Signs

Objective changes in the body that can be directly observed, such as fever and rash.

Symptoms

Subjective changes experienced by the patient, such as pain and loss of appetite.

Disease syndrome

Set of characteristic signs and symptoms for a disease.

Zoonoses

Infections passed from animal to human.

Reservoir

Natural environmental location in which the pathogen normally resides and multiplies.

Vector

Organism that spreads disease from one host to another, such as mosquitoes, ticks, and fleas.

Airborne Transmission

Transmission of pathogens via droplets or droplet nuclei.

Droplets

Direct transmission particles up to 2 mm in diameter produced when liquids are placed under force.

Droplet nuclei

Indirect transmission particles 1 to 5 μm in diameter that may remain airborne for hours or days.

Contact Transmission

Transmission involving the coming together or touching of source/reservoir and host.

Direct contact

Physical interaction between source/reservoir and host, such as kissing or touching.

Indirect contact

Involves an inanimate object (fomite), such as eating utensils or bedding.

Vehicle Transmission

Transmission involving inanimate materials that transmit pathogens, such as food or water.

Vector-Borne Transmission

Transmission by a direct living transmitter of a pathogen, often arthropods.

Vertical Transmission

Occurs when the unborn child acquires a pathogen from an infected mother.

Infectious dose 50 (ID50)

Number of pathogens that will infect 50% of inoculated hosts.

Lethal dose 50 (LD50)

Dose that kills 50% of experimental animals within a specified period.

Adherence

Mediated by special molecules called adhesins, crucial for establishing infection.

Colonization

Establishing a site of microbial replication on or within the host without necessarily causing tissue invasion.

Bacteremia

Presence of viable bacteria in the blood.

Septicemia

Bacterial or fungal toxins in the blood.

Exotoxins

Soluble, heat-labile proteins that are among the most lethal substances known.

Endotoxin

Lipopolysaccharide in Gram-negative cell wall that can be toxic to specific hosts.

Mycotoxins

Toxins produced by fungi, commonly found as contaminants of food crops.

Aflatoxins

Toxins produced by parasitic fungi that cause chronic and acute liver disease and liver cancer.

Stachybotrys

A type of fungus that produces satratoxins, potent inhibitors of DNA, RNA, and protein synthesis; induces inflammation, disrupts surfactant phospholipids in the lungs, and may lead to pathological changes in tissues.

Epidemiology

Science that evaluates occurrence, determinants, distribution, and control of health and disease in a defined human population.

Epidemiologist

One who practices epidemiology.

Sporadic disease

Occurs occasionally and at irregular intervals.

Endemic disease

Maintains a relatively steady low-level frequency at a moderately regular interval.

Hyperendemic diseases

Gradually increase in frequency above endemic level but not to epidemic level.

Outbreak

Sudden, unexpected occurrence of disease; usually focal or in a limited segment of population.

Epidemic

Outbreak affecting many people at once; sudden increase in occurrence above expected number.

Index case

First case in an epidemic.

Pandemic

Increase in disease occurrence within a large population over at least two countries around the world.

Prevalence

Total number of cases in population divided by total population.

Morbidity rate

Number of new cases during a specific period divided by number of individuals in population.

Mortality rate

Number of deaths due to given disease divided by total number of cases of the disease.

Infectious disease

Disease resulting from an infection by microbial agents.

Communicable disease

Can be transmitted from one host to another.

Common source epidemic

Epidemic caused by a single common contaminated source (food or water).

Propagated epidemic

Epidemic that starts with one infected individual into a susceptible group, with infection propagated to others.

Herd immunity

Resistance of a population to infection and pathogen spread because of immunity of a large percentage of the population.

Herd immunity level

Recommended that 80% to 95% of the population be immunized against common infectious diseases to provide necessary protection.

Systematic Epidemiology

Focuses on ecological and social factors that influence development and spread of emerging and reemerging diseases.

Emerging and Reemerging Infectious Diseases

Increases due to world population growth, urbanization, inadequate public infrastructures, increased international travel, mass migrations, climate change, habitat disruption, and microbial evolution.

Nosocomial Infections

Healthcare-acquired infections from pathogens within a hospital or clinical care facility, affecting 5 to 10% of all hospital patients.

Healthcare-Associated Infections (HAIs)

Infections sourced from endogenous or exogenous pathogens, impacting patient health within healthcare settings.

Endogenous Pathogen

Pathogen brought into the hospital by a patient who is colonized after admission.

Exogenous Pathogen

Microbiota other than the patient's, potentially sourced from hospital staff, other patients, visitors, or environmental factors.

Control Measures for Nosocomial Infections

Includes reducing or eliminating sources of infection and increasing herd immunity through immunization.

Impact of Nosocomial Infections

Prolong hospital stays by 4 to 14 days, result in additional $28 to $33 billion per year in healthcare costs, and cause approximately 99,000 deaths annually.

Vaccine

Preparation of microbial antigens used to induce protective immunity, which may include killed, living, weakened microbes, or inactivated toxins.

Immunization

Result obtained when a vaccine stimulates immunity in the host.

Adjuvants

Nontoxic materials mixed with antigens in vaccines to enhance the immune response.

Acellular or Subunit Vaccines

Vaccines that use purified molecules from microbes to avoid risks associated with whole-cell vaccines.

Haemophilus influenza type b Vaccine

Polysaccharide-protein conjugate or bacterial polysaccharide used as a subunit vaccine.

Neisseria meningitides Vaccine

Polysaccharides of serotypes A/C/Y/W-135 used in subunit vaccines.

Streptococcus pneumoniae Vaccine

Contains 23 distinct capsular polysaccharides as a form of subunit vaccine.

Hepatitis B Virus Vaccine

Recombinant surface antigen (HbsAg) used as a vaccine.

Human Papillomavirus Vaccine

Recombinant protein subunits used in vaccination.

Toxoids

Inactivated exotoxins used in vaccines, such as those from Corynebacterium diptheriae and Clostridium tetani.

Recombinant-Vector Vaccines

Vaccines that use nonvirulent viruses or bacteria to express pathogen genes encoding major antigens.

DNA Vaccines

Vaccines that introduce DNA directly into host cells, leading to the expression of pathogen DNA fragments.