Infectious Diseases Immunology

1
Infectious DiseasesImmunology

• LATG Chapters 10-11

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Health Maintenance

• Maintaining lab animal health requires
• Proper environment.
• Proper food and water.
• Disease prevention program.
• Disease detection program.
• Contingency plan if disease is detected.

3
Disease Prevention

• Type of program depends upon species.
• Rodents--primarily review of vendor data and
  procedures in place to prevent introduction and
  spread of disease.
• Nonrodents--As for rodents but may also have
  other facets such as vaccinations, dewormings etc.

4
Disease Detection

• Like NORAD, PADDS (Pfizer Animal Disease
  Detection System) relies on
• Early warning system--technicians who check
  animals daily.
• Early response--veterinary technicians who
  evaluate reported problems.
• Final response--delivered after evaluation and
  consultation with veterinarian and PI.

5
Disease Detection

• A rodent sentinel program is in place to screen
  for potential viral, bacterial and parasitic
  contaminants.
• In the rare instance of an actual infection steps
  are taken to evaluate the extent of the infection
  and eliminate it.

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Pathogenic Organisms

• Life forms that have the potential to cause
  disease under the proper conditions.
• Text classifications
• Bacteria
• Fungi
• Viruses
• Parasites

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Biology Influencing Organisms

• In laboratory animal science we are also very
  concerned with biology influencing organisms.
• These organisms may or may not cause clinical
  disease.
• Biological systems can be influenced even by
  subclinical infections.

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Viruses

• Small particles made up of nucleic acid and a
  protein capsule.
• Viruses may also be covered by an envelope
• Many viruses can infect laboratory animals, most
  do not cause clinical disease.
• Viruses are divided into two main classes.
• DNA viruses
• RNA viruses

9
DNA Viruses of Mice

• Mousepox (Ectromelia)
• Minute virus of mice
• Cytomegalovirus
• Polyoma virus
• Mouse parvo virus

10
DNA viruses of rats

• Polyoma virus (in nude rats)
• Adenovirus
• Kilham rat virus
• Rat parvo virus

11
RNA viruses of mice

• Mouse hepatitis virus (MHV)
• Sendai
• Lymphocytic choriomeningitis
• Reovirus
• Hantavirus
• Retroviruses--mouse leukemia virus and mouse
  mammary tumor virus

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RNA viruses of rats

• Sialodacryoadenitis virus (SDAV)
• Sendai
• Pneumonia virus of mice
• Hantaan virus

13
Bacteria

• Many bacteria in nature are beneficial.
• In nearly all mammals there are more bacterial
  cells than mammalian cells
• Consist of a cell membrane, a cell wall and
  cytoplasm.

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Bacteria

• Classified by
• Morphology
• Size
• Staining characteristics
• Formation of spores
• Nutrient requirements
• Biochemical reactions
• All are prokaryotes

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Bacterial Morphology

• Cocci (spherical)
• Pairs--Diplococci
• Chains--Streptococci
• Clusters--Staphylococci
• Rods, may be straight or slightly curved
• Spiral shaped

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Bacterial Staining Characteristics

• Classified into Gram negative and Gram positive
  groups
• Gram positive--dark blue/violet stain, due to a
  thick cell wall
• Gram negative--red stain, due to a thin cell wall
  with high lipid content

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Fungi

• Many fungi in nature are beneficial
• Used to make
• bread
• beer
• wine
• antibiotics
• A few fungi are pathogenic
• All are eukaryotes

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Beneficial fungus

• Saccharomyces cervisae

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Fungi

• Pathogenic species classified into
• Superficial mycoses
• Systemic mycoses

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Superficial mycoses

• Infect superficial tissues skin, hair and nails.
• Commonly called ringworm
• See scaliness and alopecia (hairloss), sometimes
  redness

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Systemic mycoses

• Infect deep tissues lung, bone, CNS, GI tract.
• Often associated with certain geographic areas
• Lower Sonoran desert--Coccidioides immitis
• Central and southeastern US--Blastomyces spp.

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Parasites

• Large group of single cell (protozoans) and
  multi-cell (metazoans) animals which must coexist
  on another animal during some part of their life
  cycle
• A parasite must also have the potential for
  causing disease in the host

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Parasites

• Websites of interest
• Parasites and Parasitological Resources
• http//www.biosci.ohio-state.edu/parasite/home.ht
  ml
• Identification and Diagnosis of Parasites of
  Public Health Concern
• http//www.dpd.cdc.gov/DPDx/Default.htm

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Parasite Lifecycles

• If you know the enemy and know yourself, you
  need not fear the result of a hundred battles.
  Sun-tzu, The Art of War
• Knowing the life cycle of a parasite is the key
  to knowing how to prevent and treat infestation.

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Parasite Lifecycles

• Life cycles can be direct or indirect.
• Direct--parasite eggs/larva can infect definitive
  host
• Indirect--parasite needs to pass through an
  intermediate host prior to infecting the
  definitive host

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Parasite Hosts

• Definitive host--the species of animal
  responsible for housing the reproductive stage of
  the parasite
• Intermediate host--the species of animal
  responsible for housing any of the
  non-reproductive stages of the parasite
• Disease can occur in both types of host

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Protozoan Parasite

• Amoebas
• Flagellates
• Ciliates
• Sporozoa

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Toxoplasma gondii

• A sporozoan parasite
• Definitive host--cat
• Intermediate host--almost any other mammal or
  bird
• Causes self-limiting diarrhea in cats
• May cause severe disease in immunosuppressed
  intermediate host

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Toxoplasma gondii

• Trophozoites in lung fluid from an HIV-infected
  person
• Tissue cyst from a cat

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T. gondii life cycle
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Other protozoa

• Giardia
• Trypanosome

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Metazoan Parasites

• Trematodes--Flukes
• Cestodes--Tapeworms
• Nematodes
• Arthropods--insects, ticks, mites

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Cestodes--Tapeworms

• Parasites which inhabit the GI tract of the
  definitive host
• May cause lesions in many different tissues in
  the intermediate host
• Do not have their own digestive system
• Life cycle often indirect but may also be direct

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Echinococcus granulosus
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Tapeworm tissue cysts
Cysts in a baboon heart
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Hymenolepis (Rodentolepis) nana

• A tapeworm of rodents and humans
• Has a direct life cycle

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Nematodes--The Roundworms

• Worms that are round in cross-section
• Body structure contains a GI tract as well as
  reproductive organs
• Both direct and indirect life cycles
• May live in many tissues in both the intermediate
  and definitive hosts

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Ascarids

• Common intestinal parasite of dogs, cats, swine
  and humans
• Also called roundworms
• Both direct and indirect life cycles
• Infections in humans can result in visceral
  larval migrans or ocular larval migrans

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Toxacara canis life cycle
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Toxocara canis

• Adults
• Egg

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Dirofilaria immitis Heartworm

• A nematode parasite that lives in the right side
  of the heart in dogs and occasionally cats
• Life cycle of this parasite requires passage
  through mosquitoes
• Infection can cause heart failure

42
Heartworm life cycle
43
Acanthocephalans

• Thorny headed worms
• Seen in pigs and nonhuman primates

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Arthropod parasites

• Large group of external parasites that include
• Insects
• Ticks
• Mites

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Arthropod parasites

• In lab animal science most likely to see
• Mites
• Lice
• Fleas

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Mites

• Parasites in the arachnid family
• Have eight legs in the adult stage
• Live on the skin, sometimes deep in the hair
  follicle
• May be zoonotic

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Sarcoptic mange mite

• Sarcoptes scabiei with multiple subspecies
• Infest a multitude of species
• Infestation is also called scabies
• Can cause intense pruritis
• Infestation is worse if animal is immunosuppressed

48
Sarcoptic mange in a dog
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Scabies in a person
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Prevention of Infectious Disease

• In all cases its easier to prevent diseases than
  to treat them
• Principles of prevention are simple and usually
  more cost-effective than treatment

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Principles of Prevention

• Purchase disease free animals
• Ship them correctly
• Receive them correctly
• Use proper practices to keep them disease free
• Have detection methods in place
• Have a plan for therapy if needed

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LATG Lecture Series
Immunology
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Historical Background

• In 1790s, Edward Jenner observes that milkmaids
  who had contracted cowpox (vaccinia virus) were
  immune to smallpox
• In 1797, Jenner inoculates a boy with material
  from a cowpox lesion, then intentionally infects
  him with smallpox
• Luckily for the inoculated boy, Jenners
  reasoning was correct and the boy was immune

54
Historical Background

• Why did Jenners technique work?
• Smallpox and vaccinia viruses are closely
  related, allowing cross-protective immune
  responses

55
Historical Background

• In 1870s , Louis Pasteur accidentally discovers
  the concept of an attenuated vaccine while
  studying fowl cholera
• Chickens infected with an old culture of fowl
  cholera bacteria, Pasteurella multocida, became
  sick but survived and became immune to lethal
  challenge with virulent bacteria
• Attenuation loss of virulence

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Historical Background

• Pasteur extended the attenuation concept to other
  infectious diseases.
• Sheep vaccinated with heat-treated anthrax
  bacillus were protected against challenge with
  live anthrax
• Administers an attenuated rabies virus vaccine to
  a boy who had been bitten by a rabid dog.

57
The Immune System

• Immunity ability to resist diseases caused by
  foreign infectious (contagious) agents.
• Bacteria (e.g. streptococcus, E. coli)
• Viruses (e.g. influenza, HIV, polio)
• Parasites (e.g. protozoan and helminthic)
• Prions (e.g. mad cow disease, scrapie)
• Fungi (crytococcus, candida)
• Some evidence for protection from proliferative
  diseases caused by cancer cells
• Also involved with allergy, transplantation,
  autoimmunity, immunodeficiency, etc.

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Pathway to Infectious Disease
59
Pathway to Infectious Disease

• Exposure?Infection?Disease?Death
• Host Immunity - operates at two basic levels to
  restrict progression to disease and death. These
  are termed innate and adaptive immunity.
• Exposure?Infection (innate)
• Exposure?Infection?Disease (adaptive)
• Exposure?Infection?Disease?Death (adaptive)

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Innate vs. Adaptive Immunity

• Innate
• nonspecific and nonadaptive
• Basic resistance mechanisms that an individual is
  born with (requires no prior experience)
• First line of defense against invading pathogens
• Acts within minutes to hours
• Broadly recognizes certain features shared by
  various classes of microorganisms
• bacterial cell walls
• double-stranded RNA of some viruses

61
Innate vs. Adaptive Immunity

• Adaptive
• Specifically recognize and selectively eliminate
  invading pathogens
• Requires several days to a week for optimal
  induction the first time a pathogen is
  encountered (sometimes not fast enough!)
• Backs-up the innate response against specific
  infectious agents, parasitic infections and
  neoplastic (cancer) transformations.
• Mediated by lymphocytes (B and T cells) and
  antigen presenting cells (macrophages, dendritic
  cells and B cells)

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The Innate Immune Response

• Anatomic (External) Barriers
• Skin (mechanical barrier)
• Mucous membranes (normal flora competes mucus
  traps microorganisms and cilia propels them out
  of the body)
• Physiological Barriers
• Temperature (e.g. fever)
• Low pH of stomach, skin
• Chemical mediators (lysozyme, interferons,
  complement, fatty acids)
• Species specific physiological differences

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The Innate Immune Response

• Phagocytic Barriers
• Phagocytic cells such as macrophages ,
  neutrophils, Natural Killer cells engulf and
  destroy pathogens
• Inflammatory Barriers
• Vasodilation, increased vascular permeability
• Production of inflammatory mediators such as
  C-reactive protein, histamine, kinins
• Species, sex, nutrition, fatigue, age, and
  genetic constitution are influencing factors.

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The Adaptive Immune Response

• Specificity
• Capacity to distinguish among various molecules
  (antigens) produced by pathogens
• Mediated by antigen recognition molecules -
  antibodies, T cell receptor, MHC
• Diversity
• Capacity to react with an almost limitless
  variety of antigens (gt109 different antibodies
  can be produced)

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The Adaptive Immune Response

• Memory
• Ability to remember a previous encounter with
  an antigen
• Secondary response is typically induced more
  quickly and is considerably more vigorous than
  the primary response
• Immunological memory can be exploited by
  vaccination
• Self/nonself recognition
• Ability to respond to and eliminate foreign
  antigens without bringing harm to ones own
  tissues

66
The Adaptive Immune Response

• Humoral immune response
• the production and secretion of soluble antibody
  molecules that neutralize and/or destroy
  infectious agents
• Cell-mediated immune response
• the generation of active lymphocytes that work at
  close range to destroy infectious agents,
  parasites or other cells

67
Defense Cells of the Adaptive Immune System

• B Lymphocytes (B Cells)
• Provide antibody-mediated immunity
• Originate in the bone marrow in higher
  vertebrates and the bursa of Fabricius in birds
• Develop into plasma cells that produce and
  secrete antibody

68
Defense Cells of the Adaptive Immune System

• T Lymphocytes (T Cells)
• Develop in the thymus
• Provide cell-mediated immunity
• Serve as helper or regulator cells to B cells
• Release lymphokines or cytokines that activate
  macrophages
• Macrophages
• Attack and destroy viral-infected cells and
  cancer cells
• inhibit certain white blood cells from migrating
  away from areas in which they are needed

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Defense Cells of the Adaptive Immune System

• Lymphocytes circulate from the bloodstream
  through the spleen, the lymph nodes, the thoracic
  duct and back into the bloodstream.

70
Organs of the Immune System

• Primary Lymphoid Organs
• Thymus
• Bone Marrow
• Secondary or Peripheral Lymphoid Organs
• Lymph Nodes (tissue)
• Spleen (blood)
• Gut-associated lymphoid tissue (Peyers patches)
• Tonsils

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Antigen Processing for the Adaptive Immune
Response

• Recognition
• self or nonself
• requires interactions between a signal molecule
  and a receptor molecule
• Processing
• transmission of the received signal from the
  receptor to other molecules and cells
• mediated by cytokines
• Response

72
Antigen Processing for the Adaptive Immune
Response

• Response
• Organism responds with active immunity against
  nonself antigens
• Humoral and/or cellular immunity depends on
• antigens chemical structure
• living or dead organism
• concentration
• route of inoculation
• Second response to the same antigen is quicker
  and stronger than the first (Anamnestic Response)

73
Humoral Immune Response

• Antibodies (Abs)
• Also known as Immunoglobulins (Ig)
• Produced by B lymphocytes
• May be membrane bound or found in serum, the
  fluid portion of blood
• Bind to specific sites on antigens or infectious
  organisms
• IgA, IgM, IgG, IgE, IgD

74
Humoral Immune Response

• Antibodies
• Symmetrical molecule, 2 heavy and 2 light chains
• Composed of polypeptides (protein) and
  carbohydrates
• Antigen combining or binding site reacts with
  antigen
• Antibodies Complement - lyse (cause to break
  apart) bacteria and infected cells

75
Immunoglobulins

• IgG
• Most abundant serum Ab
• Only Ig that crosses placenta, conferring
  immunity to the fetus
• Also transferred in the colostrum (first milk)
  after birth
• Associated with secondary anamnestic response

76
Immunoglobulins

• IgM
• Second most abundant Ig
• First Ig produced by fetus
• First produced in primary immune response to an
  antigen
• IgM titer (concentration) drops as IgG rises
• May be on membrane of B cells

77
Immunoglobulins

• IgA
• Found in mucus secretions of the intestines,
  lungs, nose and urogenital tract
• Also found in tears, bile, saliva and milk
  (colostrum)
• Helps protect body surfaces from invasion by
  bacteria and viruses
• Common Mucosal Immune System

78
Immunoglobulins

• IgE
• Found in very low concentrations
• Levels increase during parasitic infections and
  other allergic reactions
• Attaches to mast cells and basophils which
  release chemicals like histamine that produce
  inflammation and cause tissue damage
• Over response with IgE associated with
  hypersensitivity reactions such as hay fever,
  food and skin sensitivities, other allergies and
  asthma

79
Immunoglobulins

• IgD
• Not much known
• Sometimes found with IgM on membranes of B cells
• may be involved in the recognition process and in
  the activation of B cells

80
Humoral Immune Response

• Primary Immune Response
• Lag Phase
• Log Phase
• Plateau Phase
• Decline Phase

81
Humoral Immune Response

• Secondary or Anamnestic Immune Response
• Response to the same antigen is more rapid and
  the antibody levels rise higher and last longer
  than in Primary response
• Peaks 2-3 weeks later
• Gradual decline over weeks or months
• Additional boosters result in stronger anamnestic
  responses

82
Cell-mediated Immune Response

• Mediated by long-lived T cells originating in the
  thymus
• T cells stimulated by an antigen divide into
  memory cells and killer cells (cytotoxic T
  lymphocytes, CTLs)
• Lymphocyte blastogenesis - the production of new
  lymphocytes

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Types of Immunization

• Passive Immunization
• Transfer of Abs from an immune animal to a
  nonimmune animal
• Develops immediately after transfer
• Temporary immunity, Ab degrades over several
  weeks
• Examples - Abs in colostrum, Abs crossing
  placenta, antiserum injections

84
Types of Immunization

• Active Acquired Immunity
• Produced by an animal in its own body in response
  to exposure to a foreign antigen
• Develops slowly after exposure to antigen
• Longer, stronger protection than Passive
  Immunization, especially with periodic
  re-exposure
• Memory

85
Types of Immunization

• Vaccines
• Live, attenuated whole organism vaccines
  stimulate the best immune response but have the
  risk of disease transmission (oral polio,
  measles, rabies, vaccinia)
• Dead organism vaccines are more stable in
  storage, have no risk of disease and suppress
  contaminating organisms
• Adjuvants mixed with vaccines enhance the immune
  response by prolonging the presence of antigen in
  the tissue

86
Transplantation of Organs

• Histocompatiblity of donor and recipient
  determines success
• Identical twins and inbred animals

87
Diseases of the Immune System

• Autoimmune Disease
• An organisms immune system mistakenly recognizes
  self as nonself
• Immune response attacks its own tissues
• Autoimmune hemolytic anemia - red blood cells
  destroyed leading to severe anemia
• Multiple Sclerosis - myelin sheath protecting
  nerves

88
Diseases of the Immune System

• Immunodeficiency Disease
• Primary immunodeficiency disease
• innate error of metabolism or inherited genetic
  disease
• Athymic nude mouse - lack T cells
• Secondary immunodeficiency disease
• more common than primary immunodeficiency disease
• Caused by infectious disease, cancer, aging, poor
  nutrition, immune suppressing drugs
• FeLV, HIV

89
Diseases of the Immune System

• Chronic Immune Complex Disease
• Chronic infections produce a prolonged elevation
  of soluble antigens in the blood
• Immune complex formed between antigen and bound
  antibody and deposited in tissues, particularly
  the kidneys (immune complex glomerulonephritis)