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Infectious Diseases Immunology. LATG: Chapters 10-11. 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.

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Infectious diseases immunology l.jpg

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.

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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.

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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.

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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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  • 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

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DNA Viruses of Mice

  • Mousepox (Ectromelia)

  • Minute virus of mice

  • Cytomegalovirus

  • Polyoma virus

  • Mouse parvo virus

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DNA viruses of rats

  • Polyoma virus (in nude rats)

  • Adenovirus

  • Kilham rat virus

  • Rat parvo virus

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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

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  • 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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  • 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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  • 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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  • 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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  • 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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  • Websites of interest

  • Parasites and Parasitological Resources


  • Identification and Diagnosis of Parasites of Public Health Concern


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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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Other protozoa

  • Giardia

  • Trypanosome

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Metazoan Parasites

  • Trematodes--Flukes

  • Cestodes--Tapeworms

  • Nematodes

  • Arthropods--insects, ticks, mites

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  • 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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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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  • 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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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

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  • 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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  • 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

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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

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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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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

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Historical Background

  • Why did Jenner’s technique work?

    • Smallpox and vaccinia viruses are closely related, allowing cross-protective immune responses

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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

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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.

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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

  • 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

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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 (>109 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 one’s own tissues

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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

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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

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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.

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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

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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

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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)

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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

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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

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  • 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

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  • 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

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  • 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

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  • 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

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  • 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

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Humoral Immune Response

  • Primary Immune Response

    • Lag Phase

    • Log Phase

    • Plateau Phase

    • Decline Phase

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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

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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

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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

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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

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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

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Transplantation of Organs

  • Histocompatiblity of donor and recipient determines success

  • Identical twins and inbred animals

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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

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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

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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)