MODULE 1 - Pathogens and the Body's Defense System

pathogens

bacteria, fungi, viruses

bacteria, fungi and viruses can target specific organs or multiple body systems. This is known as being ________

pansystemic

bacteria is defined as

single celled organisms within the power to divide and multiple

each ____ of bacteria has different shapes and characteristics

strain

many forms of bacteria are _______ and even helpful to an animal’s body

harmless

there are bad strains of bacteria that cause _____ in both humans and companion animals

disease

Key facts about bacteria

• single celled, capable of dividing and multiplying

• spread through direct contact

• have a simple structure without a true nucleus or membrane bound organelles

  • many bacteria are harmless or beneficial, but some strains cause disease in humans and companion animals

• found in various environments — animals, humans, air, water, soil, plants

• each strain has a different shape and characteristic

Basic components of bacteria

• cell wall

• plasma membrane

  • capsule (in some bacteria)

cell wall

provides structural support and protection

plasma membrane

surrounds the cytoplasm and distinguishes it from the external environment

capsule

aids in evading the host’s immune system

How bacteria can cause disease:

entry to host

adherence to cells

colonization and multiplication

evasion of immune system

production of toxins

inducing inflammation

disruption of normal functions

entry to host

ingestion: consuming contaminated food or water

inhalation: breathing in airborne bacteria

skin contact: entering through cuts, wounds, or mucous membranes

vectors: being transmitted by insects or other animalsa

adherence to host cells

once in body, bacteria must adhere to host cells to establish an infection

they use structures like pili or fimbriae to attach to surfaces of the cells in resp tract, GI tract, or other tissues

colonization and multiplication

after adhering to cells, bacteria colonize and multiply

form colonies on the surface of tissues or invade deeper into body

evasion of the immune system

capsules: some bacteria produce a protective capsule that prevents them from being engulfed by white blood cells

antigenic variation — changing their surface proteins to avoid detection by the immune system

inhibiting phagocytosis — producing substances that inhibit the ability of white blood cells to engulf and destroy them

production of toxins

can damage host tissues and disrupt normal cellular functions

exotoxins — secreted by bacteria that can cause damage to specific tissues or organs

—- example: clostridium botulinum, produces botulinum toxin which affects the nervous system

endotoxins: components of the bacterial cell wall that are released when the bacteria die and break apart. endotoxins can cause inflammation, fever, and septic shock

inducing inflammation

presence of bacteria and their toxins can trigger an inflammatory response in the host

inflammation is the body’s way of trying to contain and eliminate infection, but can also cause tissue damage and contribute to the symptoms of disease

disruption of normal functions

resp infections — bordetella and other bacteria can cause, leads to diffculty breathing, nasal discharge

GI infections: bacteria such as salmonella can cause. V/D, abdominal pain

systemic infections: staphylococcus aureus — spread through bloodstream, and affecting multiple organs

structure of fungi

fungi or fungus

any member of the eukaryotic organisms (any cell or organism that possesses a clearly defined nucleus)

• yeasts

• molds

• mushroomlike microorganisms

Key Points about Fungi

pathogenic fungi are parasitic, spore-producing organisms

obtain nourishment by absorbing food from their hosts

many species exist in the environment, but only a few cause infections

can be acquired by:

• inhalation

• ingestion

• skin contact

some fungal infections can affect healthy animals; other require immunosuppressive agents or host that is immunocompromised

prolonged use of antimicrobial drugs or immunosuppressive agents increases the likelihood of fungal infections

Fungal diseases

• localized or systemic

• may be confined to surface (ringworm) or become systemic (systemic mycosis)

  • affect various parts of the body; each species having preferred locations (lungs, eyes, lymph nodes

types of fungi that commonly affect pets are abundant in ____ and tend to adhere to specific geographic locations

soil

Histoplasmosis location

midwest/south (texas, OK, colorado)

blastomycosis location

north and south (michigan and wisconsin, NC, SC, GA)

C gatti cryptococcosis location

california, washington, oregon

systemic fungal diseases tend to affect three types of pets most commonly:

young, large breed dogs

pets that have a weakened immune system

pets that are taking cyclosporine

how fungi cause disease

entry to host — inhalation, skin contact, ingestion

adherence and colonization — once inside body, adhere to tissues and begin to colonize. can grown on surface of tissues or invade deeper into body

evasion of immune system — thick cell walls: providing protection against immune responses, changing forms: switching between yeast and mold forms to avoid detection

tissue damage — direct evasion: evading and destroying host cells, enzyme production: break down host tissues, facilitate further evasion

inducing inflammation — inflammatory response leads to redness, swelling, painVir

Virus characteristics

• obligate intracellular pathogens

• small microbes that cannot replicate or live outside cell

• debate whether viruses are living organisms

• no cell wall, able to reproduce independently

• composed of nucleic acid core (DNA/RNA) surrounded by protein capside

• can be enveloped (lipoprotein coating) or non-enveloped

• promote replication, not necessarily to kill host

virus structure

steps of viral infection

1. Attachment - binds to specific receptors on host surface

2. absorption/penetration - invades host cell, breaks down capsid, injects genetic material into cytoplasm

3. Biosynthesis - inhibits host cells DNA, RNA, or protein synthesis. Uses host cell’s resources to reproduce viral genome and proteins

4. Assembly - new virions are formed inside host cell

5. Release - leave host cell via exocytosis (enveloped viruses) or lysis (non-enveloped viruses)

   1. possible outcomes include minimal host cell damage, host cell destruction, or malignant transformation

Bacterial diseases

Leptospirosis

bordetella

brucellosis

salmonellosis

tetanus

hemorrhagic septicemia

anthrax

fungal diseases

cryptococcus

blastomyces

histoplasma

aspergillus

coccidiodes

candidiasis

viral diseases

panleukopenia

rhinotracheitis/calcivirus

FIV

FeLV

FIP/Feline Coronavirus

Rabies

Distemper

Parvovirus

Canine Influenza

Lyme

Toxoplasmosis

Canine Monocytic Ehrlichiosis

Nonspecific immunity

composed of many elements, responds to any pathogen in the same way every time

• species resistance: genetic ability of a species to defend against certain pathogens

• mechanical/physical and chemical barriers: skin and mm = mechanical, chemical = sebum, mucus, enzymes

  • healthy skin = first line of defense

• inflammatory response

  • Activated when tissues are invaded or injured. 

  • Mediators attract white blood cells, dilate blood vessels, and increase permeability. 

  • Signs: Heat, redness, swelling, pain. 

  • Neutrophils perform phagocytosis to eliminate invaders.

• interferon and complement

  • interferon = prevents viral replication within host cells

  • complement = enzymes that create holes in invading cell walls, causing lysis

Specific immunity

third line of defense/final defense

• cell mediated immunity

  • T cell lymphocytes

  • T cells recognize and destroy pathogens directly

  • origin: bone marrow, mature in thymus

  • rapid and targeted response

• Humoral immunity

  • conducted by B-cell lymphocytes

  • B cells produce antibodies in response to specific antigens

  • origin: bone marrow or bursa of Fabricus

    • slower respone, involves memory cells for quicker future responses

differential immunity chart

other immunity types

species resistance

mechanical barriers

chemical barriers

species resistance

Definition: The genetic ability of a particular species to provide defense against certain pathogens.

Example: Canines do not acquire feline leukemia virus, and felines do not contract canine distemper virus. 

mechanical barriers

Definition: Physical structures that prevent the entry of microorganisms into the body.

Example: The skin and mucous membranes act as a barrier to protect underlying tissues from injury and infection. 

chemical barriers

1. Definition: Substances produced by the body that inhibit or destroy pathogens.

   Example: Sebum, mucus, and enzymes produced by the skin and mucous membranes that act to inhibit or destroy pathogens  

inherited immunity

• Genetic factors influencing immunity before birth/ is the immune system that is inherited 

acquired immunity

• Develops after birth. 

• Natural: Result of exposure to pathogens. 

• Artificial: Result of vaccinations. 

Acquired Immunity: 

Learns from previous encounters, responds more effectively upon re-exposure. 

passive immunity

• Transfer of antibodies from one animal to another (through placenta, blood products, injections) 

• Provides immediate but temporary protection. 

active immunity

• Animal's own immune system produces a response to a pathogen. 

• Provides long-lasting protection. 

• Virus-Host Interaction: 

  • Inherited /Innate Immunity: Destroys many viruses before they infect cells.

  • Acquired immunity: Antibodies recognize viral proteins, prevent cell entry, and target the virus for destruction. 

Vaccination

utilizes humoral response by introducing antigens to stimulate antibody production

type of vaccines

killed virus — inactive, incapable of causing disease

modified live virus — genetic material altered to reduce virulence

vaccination mechanism

process — initial antigen exposure triggers antibody production

booster shots — enhance and prolong antibody response

anamestic response — memory response from immune system leading to faster and stronger reaction upon re-exposure

importance of multiple injections

• Maternal Antibodies: Received at birth, protect initially but can interfere with vaccine efficacy.

• Vaccination Schedule: 

  • Start at 8 weeks, boosters every 3-4 weeks until 12-16 weeks. (Depends on age starting if older than this).

    • Certain breeds (e.g., Rottweilers, Dobermans) may require longer schedules. 

• Risk of Infection: 

  • Window where maternal antibodies block vaccines but don’t protect against infection, leading to potential vulnerability. 

cat vaccines

dog vaccines