Download Health, Gnotobiology and Infectious Diseases

LATG: Chapters 10-11
Infectious Diseases
Immunology
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.
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.
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.
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.
Pathogenic Organisms
• Life forms that have the potential to
cause disease under the proper
conditions.
• Text classifications
– Bacteria
– Fungi
– Viruses
– Parasites
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.
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
DNA Viruses of Mice
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Mousepox (Ectromelia)
Minute virus of mice
Cytomegalovirus
Polyoma virus
Mouse parvo virus
DNA viruses of rats
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Polyoma virus (in nude rats)
Adenovirus
Kilham rat virus
Rat parvo virus
RNA viruses of mice
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Mouse hepatitis virus (MHV)
Sendai
Lymphocytic choriomeningitis
Reovirus
Hantavirus
Retroviruses--mouse leukemia virus
and mouse mammary tumor virus
RNA viruses of rats
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Sialodacryoadenitis virus (SDAV)
Sendai
Pneumonia virus of mice
Hantaan virus
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.
Bacteria
• Classified by
– Morphology
– Size
– Staining characteristics
– Formation of spores
– Nutrient requirements
– Biochemical reactions
• All are prokaryotes
Bacterial Morphology
• Cocci (spherical)
– Pairs--Diplococci
– Chains--Streptococci
– Clusters--Staphylococci
• Rods, may be straight or slightly curved
• Spiral shaped
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
Fungi
• Many fungi in nature are beneficial
• Used to make
– bread
– beer
– wine
– antibiotics
• A few fungi are pathogenic
• All are eukaryotes
Beneficial fungus
• Saccharomyces
cervisae
Fungi
• Pathogenic species classified into
– Superficial mycoses
– Systemic mycoses
Superficial mycoses
• Infect superficial tissues; skin, hair and
nails.
• Commonly called “ringworm”
• See scaliness and alopecia (hairloss),
sometimes redness
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.
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
Parasites
• Websites of interest
• Parasites and Parasitological
Resources
– http://www.biosci.ohiostate.edu/~parasite/home.html
• Identification and Diagnosis of Parasites
of Public Health Concern
– http://www.dpd.cdc.gov/DPDx/Default.htm
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.
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
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 nonreproductive stages of the parasite
• Disease can occur in both types of host
Protozoan Parasite
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Amoebas
Flagellates
Ciliates
Sporozoa
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
Toxoplasma gondii
• Trophozoites in lung
fluid from an HIVinfected person
• Tissue cyst from a
cat
T. gondii life cycle
Other protozoa
• Giardia
• Trypanosome
Metazoan Parasites
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Trematodes--Flukes
Cestodes--Tapeworms
Nematodes
Arthropods--insects, ticks, mites
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
Echinococcus granulosus
Tapeworm tissue cysts
Cysts in a baboon heart
Hymenolepis (Rodentolepis)
nana
• A tapeworm of
rodents and humans
• Has a direct life
cycle
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
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
Toxacara canis life cycle
Toxocara canis
• Adults
• Egg
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
Heartworm life cycle
Acanthocephalans
• Thorny headed worms
• Seen in pigs and nonhuman primates
Arthropod parasites
• Large group of external parasites that
include
– Insects
– Ticks
– Mites
Arthropod parasites
• In lab animal science most likely to see
– Mites
– Lice
– Fleas
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
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
Sarcoptic mange in a dog
Scabies in a person
Prevention of Infectious Disease
• In all cases it’s easier to prevent
diseases than to treat them
• Principles of prevention are simple and
usually more cost-effective than
treatment
Principles of Prevention
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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
LATG Lecture Series
Immunology
Historical Background
• In 1790’s, 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, Jenner’s reasoning
was correct and the boy was immune
Historical Background
• Why did Jenner’s technique work?
– Smallpox and vaccinia viruses are closely
related, allowing cross-protective immune
responses
Historical Background
• In 1870’s , 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
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.
The Immune System
• Immunity = ability to resist diseases caused
by foreign infectious (contagious) agents.
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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.
Pathway to Infectious Disease
Exposure
Infection
Disease
Resolution
No Infection
No Disease
Death
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)
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
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)
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
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 Creactive protein, histamine, kinins
• Species, sex, nutrition, fatigue, age, and genetic
constitution are influencing factors.
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 (>109 different antibodies
can be produced)
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 one’s own tissues
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
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
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
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.
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 (Peyer’s patches)
– Tonsils
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
Antigen Processing for the
Adaptive Immune Response
• Response
– Organism responds with active immunity against
nonself antigens
– Humoral and/or cellular immunity depends on:
• antigen’s 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)
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
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
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
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
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
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
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
Humoral Immune Response
• Primary Immune Response
– Lag Phase
– Log Phase
– Plateau Phase
– Decline Phase
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
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, CTL’s)
• Lymphocyte blastogenesis - the
production of new lymphocytes
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
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 reexposure
– Memory
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
Transplantation of Organs
• Histocompatiblity of donor and recipient
determines success
• Identical twins and inbred animals
Diseases of the Immune System
• Autoimmune Disease
– An organism’s 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
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
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)