320: Exam 1

Animal Sciences 320:

Lecture Two:

• Health: a state of complete physical, mental and social well-being, not merely the absence of disease or infirmity.

• Disease: A condition of the living animal or plant body or of one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms

  • Somewhat vague, what does normal necessarily mean? We need statistics.

    • Defining disease is actually pretty hard.

      • Some believe that our uses of health and disease reflect value judgments

      • Disease is relative to what people consider normal

      • One person's diarrhea is another person's normal day

• Illness: a person’s subjective experience of their symptoms. What a patient brings to the healthcare provider

• Disease: underlying pathology; biologically defined: the health care provider’s perspective

• Sickness: social and cultural conception of this condition: cultural beliefs and reactions such as fear or rejection. These affect how the patient reacts.

• Defining health and disease:

  • Naturalism:

    • Most prominent philosophical approach to defining health and disease

      • Reference class: a natural class of organisms of uniform functional design; specifically, an age group of a sex of a species

      • Normal function: part or process within members of the reference class is a statistically typical contribution by it to their individual survival and reproduction.

      • Disease: type of internal state which is either an impairment of normal function ability.

    • Criticisms:

      • Neglects the role values play in determining healthy or diseased

      • Provide definitions that rely exclusively on information from the biological sciences, but lack a basis in biological theory.

      • If you take a data sample, are you or the animal accurately represented in the study?

• Normativism:

  • Disease is deviancy from some alternative state of affairs which is considered more desirable

    • Suggests that we (both lay people and medical professionals) should use health and disease in ways that reflect our values.

    • Physiological or psychological state we desire are called health and those states we want to avoid are labeled diseased

• Criticisms:

  • Case where we agree that a state is undesirable but we disagree over whether it is a disease state

    • Overweightness, PMS

    • Values can change

• Hybrid Theories:

  • The term disease should only apply to dis-valued states with the proper biological etiology.

  • You need a value that applies specifically to the individual and has a base to back it up.

• Criticisms:

  • A state where there is no evolutionary dysfunction yet we disvalue that state

• Microbio:

  • Bacteriome

  • Mycobacterial communities

  • Virome (virus)

• Macrobiome (infancy in the knowledge field):

  • Protozoa

  • Helminths (worms, flukes)

    • We have a relationship with them, if you destroy the relationship, you can damage the immune system that prevents things like allergies.

    • Lots of kids have them, but we have treatments

• Colonization (normal flora, cells that aren't ours that live on our body):

  • Human cells (36 trillion) vs colonizing cells (39 trillion prokaryotic cells, mostly bacteria)

• “Normal Flora:”

  • Most areas of the body in contact with the outside environment harbor resident microbes

  • Microorganisms that normally reside at a given site and under normal circumstances do not cause disease

  • Normal flora is essential for health:

    • Create an environment that may prevent infections

    • Enhance host immune defenses

  • Internal organs, tissue, and fluid are microbe-free (relatively)

  • Transient Flora:

    • Occupy the body for only short periods

    • Usually picked up during daily activities

    • Surfaces (door knob, hand-shake, etc)

    • Often eliminated easily

  • Resident Flora

    • Are permanently established (or for long periods of time)

• Types of relationships with microbiome

  • Mutualism

    • Both the host and the microbe benefit

      • Ruminants and their gut microorganisms

      • E. Coli- microbe receives nutrients, but produces vitamins K and B-complex

  • Commensalism

    • One partner benefits, and the other neither benefits nor is harmed

  • Parasitism

    • One organism benefits at the expense of the host

    • An external parasite to cause infestation

    • Internal parasite to cause infection

  • Pathogenic

    • Organism causes damage to the host during infection

• Microbiomes are critical at an early age, they set things in motion

• Initial Colonization

  • Uterus and contents are normally sterile and remain so until just before birth

  • Breaking of fetal membrane exposes the infant; all subsequent handling and feeding continue to introduce what will be normal flora

  • Is this paradigm entirely correct?

    • It might have an exposure even before birth

• Triangle:

  • Microbiome→Immune system→Nutrition

• Defining Infections

  • Infectious agents: viruses, bacteria, fungi, protozoa, worms, and prions

  • Infection: condition in which infectious agent penetrates host defenses

  • Infectious disease: an infection that causes damage or disruption to tissues and organs and/or physiological homeostasis

  • Endogenous infections

    • Occurs when normal flora is introduced to a site that was previously sterile

  • Exogenous Infections

    • Caused by organisms that are not normally present in the body but have gained entrance from the environment

• Types of pathogens

  • True pathogen: infectious agent that causes disease in virtually any susceptible host

  • Opportunistic pathogen: normally harmless; causes disease when the normal flora is disrupted (i.e. by antibiotics) or when the host is immunocompromised

• Patterns of Infection:

  • Localized infection: infectious agent enters the body and remains confined to a specific tissue

  • Systemic infection: infection spread to several sites and tissue fluids, usually the bloodstream

  • Focal infection: infectious agent breaks loose for a local infection and is carried to other tissue

  • Mixed infection: several microbes grow simultaneously at the infection site (polymicrobial)

  • Primary infection: refers to the first time you are exposed to (and infected by) a specific pathogen

  • Secondary infection: another infection by a different microbe, succeeding a primary infection (getting a UTI treatment and getting a yeast infection because of it)

• What defines a particular disease

  • Signs (objective evidence): something can be detected/measured by someone else

  • Symptoms (subjective evidence): something that must be described by the one suffering from the disease

  • Syndrome: the complete set of signs and symptoms associated with a specific disease

• Patterns of infection

  • Acute infection: comes on rapidly, with severe but short lived effects

  • Chronic (persistent) infection: progresses and persists over a long period of time

• Infections that get unnoticed:

  • Asymptomatic (subclinical) infections: although infected, the host does not show any signs of disease

  • “Typhoid Mary”

    • First person in the USA identified as an asymptomatic carrier of the salmonella Typhoid Fever

• Acquisition and Transmission of infectious agent:

  • Communicable infection: infected host can transmit the infectious agent to another host

  • Non-communicable infection: infection does not arise through transmission from host to host

• Nosocomial infections

  • Infections acquired or developed during hospital stay

  • Presence of microorganisms in hospital environment→ compromised host→ chain of transmission

Lecture Four:

• Epidemiology: the study and analysis of the patterns, causes, and effects of disease and health-related factors. “The study of what befalls upon people.”

  • Epi- on, upon, befall

  • Demo- people

  • Ology- the study of

  • Major areas of epidemiological study include

    • Disease etiology

    • Transmission

    • Outbreak investigation

    • Disease surveillance

    • Forensic epidemiology and screening

    • Biomonitoring

    • Comparisons of prevention/treatment outcomes

• Epidemiologic Triad

  • Host(→vector) → environment(→vector) → agent(→vector), if you can break this link, you can control the vector

• Pathogen Traits

  • Type: viruses, bacteria, fungi, protozoa, worms, prions

    • Other info

  • Virulence:

    • Ability to cause severe disease

    • Virulence factors: specific mechanisms that allow pathogen to adhere to or penetrate host cell, thwart immune defenses, damage host

  • Infectious Dose:

    • Minimum number of pathogens required to cause illness

  • Incubation Period:

    • Time it takes after first exposure for the pathogen to cause signs and symptoms; influences extent of spread

      • Things that sleep for a long time (takes a long time to show symptoms such as HIV) are harder to control since it can spread while no symptoms are present. Things that spread fast (like COVID) can wipe an entire village before it spreads and thus doesn't spread anymore.

• Infectious Dose (ID)

  • If ID is not reached, infection will not occur

    • It is defined in a particular population, (young people vs old)

  • ID50

    • Amount of pathogenic microorganisms that will produce demonstrable infection in 50% of exposed hosts

• Signs of clinical infections

  • Latent period: exposure, but no symptoms

  • Incubation period: no signs or symptoms, but infection has begun

  • Prodromal Period: mild signs or symptoms

  • Period of illness: most severe signs and symptoms

  • Period of decline: signs and symptoms

  • Period of convalescent: illness goes away are you are back to normal health

• Host traits:

  • Immunity to Pathogen:

    • Previous exposure, immunization

    • Antigenic variation of pathogen can overcome

  • General Health:

    • Malnutrition, overcrowding, fatigue

    • Developing world more susceptible: crowding, poor nutrition, poor sanitation

  • Age:

    • Very young, elderly generally more susceptible

    • Immune system less developed in young: wanes in old.

    • Elderly also less likely to update immunizations

  • Genetic background

    • Natural immunity varies widely

    • Specific receptors critical for infection may differ in individuals

    • Sickle cell gene and resistance to malaria

  • Gender:

    • Pregnant animals are at more risk

    • Pregnant animals can pass on some diseases to offspring

  • Religious and cultural practices:

    • Breastfeeding provides protective antibodies to infant

    • Consumption of raw fish can increase exposure

• Environmental Factors:

  • Environmental factors may increase likelihood of disease transmission opportunities or lower the hosts resistance to infection

    • Heat or cold stress

    • Food availability

    • Hygiene

    • Crowding

    • Cultural practices

    • Presence of vectors or reservoirs for pathogen

• Routes of transmission

  • Direct contact: physical contact or fine aerosol droplets.

    • Some pathogens cannot survive in environment

    • Hand washing considered single most important measure for preventing spread of infectious disease

    • Horizontal vs vertical transmission

  • Indirect contact

    • Some pathogens can survive for a period outside the host

• Transmission of infectious disease

  • Fomite: inanimate object that serves a role in disease transmission

  • Vector: any agent that carries a pathogen and transmits it to human or animal hosts

  • Vehicle: typically food, water or air, that transmits a pathogen to the host

  • Reservoir: the natural habitat in which a pathogen lives and reproduces that serves as a source of infection

    • Living reservoir may be symptomatic or asymptomatic

    • Exclusively human reservoirs are easier to control

    • Non-human reservoirs challenging to control

    • Environmental reservoirs: difficult or impossible to eliminate

Lecture Five:

• Portals of entry and exit

  • Skin

  • Gastrointestinal tract: food, drink, other ingested materials

  • Respiratory tract

  • Urogenital tract

  • Transplacental

• Vehicles of entry and exit

  • feces/urine

  • semen/ vaginal secretions

  • Sputum

  • Spit

• Cycle of transmission

  • 

• Frequency of cases

  • Prevalence: total number or proportion of cases or events or conditions in a given population

  • Incidence: number of new cases during a specified time period

  • Morbidity Rate: number of people afflicted with a certain disease during a given period of time

  • Mortality rate: number of deaths in a population due to a certain disease during a given period of time

  • Case-fatality rate: percentage of people with a specific disease that dies from that disease

  • Attack rate: number of people affected by a disease divided by the number of people with a specific exposure

• Disease occurrence patterns:

  • Endemic: a relatively steady frequency over a long period of time in a particular geographic locale (common cold)

  • Sporadic: when occasional cases are reported at irregular intervals (rabies)

  • Epidemic: increasing prevalence of a disease beyond what is expected

  • Pandemic: epidemic across countries and continents

• Basic Reproductive Number (R0)

  • The average number of new infections generated by one infection in a completely susceptible population

    • EX: is R0=2, for every infected person, two people will become infected

  • Measure of the intrinsic potential of an infectious agent to spread

  • R0 = C x P x D

    • C= contact rate (contact/time)

      • The average rate of contact between susceptible and infected individuals

    • P= transmissibility (infection/contact)

      • The probability of infection given contact between a susceptible and infected individual

    • D= duration of infectiousness (time/infection)

  • 

• Effective reproductive number ®

  • A population will rarely be totally susceptible to an infection in the real world. The effective reproductive rate ® estimates the average number of secondary cases per infectious case in a population made up of both susceptible and non-susceptible hosts

  • R = R0 x S

    • R0= basic reproductive number

    • S= fraction of the host population that is susceptible

Lecture Six:

• Koch’s Postulates

  • The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.

  • The microorganism must be isolated from a diseased organism and grown in pure culture. (not all microorganisms can be put on a pure culture)

  • The cultured microorganism should cause disease when introduced into a healthy organism.

  • The microorganism must be reisolated from the inoculated, disease experimental host and identified as being identical to the original specific causative agent.

• Bacterial Shapes

  • Coccus (round ball)

  • Bacillus (rod)

  • Spiral

  • Coccobacillus

  • Vibrio (rod and spiral shape)

• Flagella

  • Presence is species/strain dependent

  • For motility

  • Number and arrangement vary

• Pili/fimbriae:

  • Hair-like structures, fimbriae shorter than pili

  • adhere/attach to surfaces

  • F or sex pilus: used for transfer of genetic material from one bacteria to another

  • Can provide resistance against engulfment by phagocytes.

• Endospore formation

  • Under stressful environments, certain gram-positive bacteria are capable of forming endospores.

• Types of Bacterial Pathogen

  • True Pathogen: infectious agent that causes disease in virtually any susceptible host

  • Opportunistic pathogen: (pseudomonas, staph), normally harmless; causes disease when the normal flora is disrupted or when the host is immunocompromised

  • Bacterial Adhesion:

    • Necessary to avoid innate host defense mechanisms

    • Adhesion is often an essential preliminary step to colonization and then penetration through tissues.

    • At the molecular level, adhesion involves surface interactions between specific receptors on host cell membrane and ligands on the bacterial surface.

    • Nonspecific surface properties of the bacterium, including surface charge and hydrophobicity, also contribute to the initial stages of the adhesion process.

• Mechanisms of Adherence to cell or Tissue surfaces

  • Non-specific adherence: reversible attachment to the surface

  • Specific adherence: irreversible permanent attachment to the surface.

  • Tissue tropism: particular bacteria are known to have an apparent preference for certain tissues over others

  • Species specificity: certain pathogenic bacteria infect only certain species of animals.

  • Genetic specificity within a species: certain strains or races within a species are genetically immune to a pathogen.

• Exotoxins: proteins produced inside the pathogenic bacteria, most commonly gram-positive bacteria, as part of their growth and metabolism. The exotoxins are then secreted into the surrounding medium during the log phase.

  • Most powerful human poisons known and retain high activity at very high dilutions.

• Endotoxins: lipid portions of lipopolysaccharides that are part of the outer membrane of the cell wall of gram-negative bacteria. The endotoxins are liberated when the bacteria die and the cell wall breaks apart.

Lecture Seven:

• Virions/Viruses

  • Acellular and the virion consist of:

    • DNA or RNA core

    • Protein coat (capsid)

    • Lipid envelope (spikes on some viruses)

  • Can infect all types of life forms including bacteria and archaea

  • Can replicate only when within living host cell

• Two systems of virus classification:

  • Hierarchical virus classification system

    • nature of the nucleic acid: RNA or DNA

    • symmetry of the capsid

    • presence of absence of an envelope

    • dimensions of the virion and capsid

  • The Baltimore classification

    • viruses can be classified into seven (arbitrary) groups

• Viral Attachment and Entry

  • Direct Penetration

  • Membrane fusion

  • Endocytosis

• Transmission → attachment absorption → Entry→ (Latency-survival in host) → replication→ shedding (pathology to Host)

• Virtual Replication

  • Uncoating

  • transcription/mRNA production

  • Synthesis of virus components

  • Virion Assembly

• Viral Shedding

  • Via Budding

  • Via Apoptosis