Exam 2 Flashcards

1
Q

Cell-mediated immunity: entirely associated with cell surfaces, T-cell receptors, that are unable ot “see” free antigens

A

T Cells: can regulate the immune responses of other cells (CD4) or indirectly kill cells (CD8) that carry specific antigens

  1. lymphocytes produced in red bone marow, migrate to thymus (primary lymphoid organ) where they mature (VDJ recombination of T cell receptor) and undergo selection
  2. T cell receptors must recognize self MHC proteins needed for activation, but not the self antigens (self tolerance) that the MHC presents (T-cell eliminated in thymus if criteria not met)
  3. “naïve” T cells recirculate only between the blood and lymphoid organs, do not enter other tissues; activated in secondary lymphoid organ
    (Ex. Spleen, tonsils, or lymph nodes)
  4. T-cell receptors are transmembrane proteins with constant and variable region, like antibodies; composed of 2 chains (alpha and beta)
  5. T-cell receptors recognize only a processed peptide fragment that the APC’s MHC presents to the T cell receptor, unlike B-cell receptors
  6. other transmembrane proteins closely linked to T-cell receptors serve as coreceptors, such as CD4 and CD8
  7. T cell activation occurs in secondary lymphoid tissue when antigen is displayed with self MHC on mature dendritic cells (DCs)
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2
Q

Cytotoxic Tcells - kill cells that are infected with viruses (or other pathogens)

A
  1. have CD8 coreceptor protein
  2. antigen-presenting cell (APC) often include dendritic cells (professional APC)
  3. activated by endogenous antigens bound to MHC class I proteins of dendritic cells
  4. activation results in the release of IL-2, TNF, and IFN-y; and they differentiate into memory cells and activated cells (clonal expansion)
  5. “altered-self” cells expresing the same combination of foreign peptide on MHC class I are targeted; may include tumor cells, virally infected cells, or cells with intracellular parasites
  6. release perforins, insert in membrane and make pores, granzymes enter infected cell and activate caspase enzymes that induce apoptosis
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3
Q

Helper Tcells

A

involved in activating and directing other immune cells;
their cytokines largely determine whether an immune response is humoral or cell-mediated; no killing ability

  1. have CD4 coreceptor protein
  2. 1st signal is initiated by exogenous antigens bound to MHC class Il proteins of macrophages, dendritic cells (phagocytosis or endocytosis), and Bcells (receptor-mediated endocytosis)
  3. 2nd signal is a verification step, naïve TH cells express the protein CD28 that must bind to costimulatory B7 protein on professional APCs; a protective measure to ensure TH cells are responding to a foreign antigen
  4. when 2nd activation signal is complete the originally undetermined T-helper null cell (TH0) releases a potent T cell growth factor called interleukin 2 (IL-2), which activates the T cells proliferation pathways
  5. TH0 cells differentiate into TH1 or TH2 cells depending cytokine environment
    -Cellular Response- IL-12 &IFN-y induces TH1 differentiation; IFN-y inhibits TH2 cells
    -Humoral Response- IL-4 drives TH2 differentiation, and inhibits TH1 cell production
  6. both T helper cell groups are able to inhibit the activation of the other group using their own cytokines
    - TH1 cells communicate attack against intracellular bacteria and protozoa
    - TH2 cells communicate attack against extracellular parasites including helminths
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4
Q

TH1 cells mainly secrete:

A

IL-2: growth factor for Tand Bcells; natural killer cells become lymphokine- activated killer (LAK) cells
IFN-Y: inhibition of TH2 cells, strong macrophage-activating factor
TNF: major mediator of inflammation; high concentrations increase synthesis of prostaglandins, resulting in fever
GM-CSF: Granulocyte-Macrophage Colony Stimulating Factor

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5
Q

TH2 cells mainly secrete:

A

IL-4: growth factor for Bcells; suppresses TH1 cell production
IL-5: stimulates Bcells for growth, differentiation, and production of antibodies; activates eosinophils
IL-10: inhibits TH1 cells, cytotoxic Tcells, NK cells, &macrophage cytokine synthesis

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6
Q

Humoral immunity: based on antibodies on cell surfaces and in body fluids (blood, lymph, etc.)

A

B Cells: bind specific to free (soluble) antigen or particulate antigen with its membrane bound antibody (B cell receptor); also serves as APC to TH cells

  1. B cells produced in red bone marrow; immunoglobulin (Ig) synthesis occurs
    - tested for auto-reactivity by the immune system before leaving the bone marrow
    - if highly reactive to self:
    Clonal deletion- removal, usually by apoptosis
    Receptor editing- opportunity to rearrange their conformation via RAG (recombination activating gene)
    Anergy- B cells enter a state of permanent unresponsiveness and fail to respond ot their specific antigen
  2. Ig is encoded by different segments of DNA, a V(variable) segment, a D(diversity) segment, a J (joining) segment, and a constant region; variable regions are shuffled by RAGs
  3. each Ig consists of 2 identical short polypeptides called light chains and 2 identical longer polypeptides chains called heavy chains; held together by disulfide bonds to form a Y-shaped molecule
  4. each “arm” is called Fab (fragment antigen-binding) region and the “stem” is called Fc (fragment crystallizable) region
  5. the heavy chain constant region is translated from 1of 5possible DNA sequences named u (mu), o (delta), y (gamma), a (alpha), E (epsilon), which give rise to a particular class of immunoglobulin
  6. immunoglobulins IgM (monomeric form) and IgD are present on mature “naïve” Bcells
  7. Bcells recirculate only between blood and lymphoid organs, activated in secondary lymphoid organ (Ex. lymph nodes, MALT, which includes tonsils and appendix)
  8. Bcells recognize their cognate antigen in its native form with its B-cell receptors (antibodies) ; each Ig can bind 2 identical epitopes
  9. binding of antigen to Ig on surface of appropriate Bcell is usually not sufficient to
    activate the B cell to multiply; so, B cell (APC) internalizes antigen-antibody complex and incorporates portions of antigen (epitope) on MHC II
  10. specific TH2 cell recognizes antigen displayed by B cell; cytokines such as IL-4 are released from TH2 cell to activate B cell; produces memory cels and plasma cells that secrete antibodies against the identical antigen
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7
Q

Complement

A
  1. consists of approx. 30 different proteins
  2. circulate freely in blood plasma, generally in inactive form (zymogen)
  3. complement can be activated by classical pathway (antigen-antibody complex) or alternative pathway (spontaneously) or lectin pathway (cell wall polysaccharides of certain bacteria and fungi)
  4. complement proteins (C3b) coat pathogen surface (opsonization), thus promoting phagocytosis and destruction by macrophages and neutrophils, which have receptors for C3b
  5. C5a is an important chemotatic protein, helping recruit inflammatory cells
  6. complement C5b initiates pathway for membrane attack complex (MAC) that forms pores in pathogens that have lipid membrane to induce lysis
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8
Q

Interferons (IFN-a, IFN-b, IFN-y)

A
  1. a class of proteins synthesized upon parasitic infection of a cell
  2. act as messengers to protect normal cells in vicinity from becoming infected
  3. IFN-a and IFN-b induce the degradation of RNA and block protein production
  4. IFN-y is produced by TH cells and natural killer cells to stimulate in the cellular response
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9
Q

Phylum: Platyhelminthes

A

Platyhelminthes (flatworms): phylum containing simplest bilateraly symmetrical animals
- most platyhelminthes are parasitic
- acoelomate body plan (no body cavity other than the gut); rarely has anus
- triploblastic (composed of three fundamental cell layers) Ex. mesoderm, ectoderm, and endoderm
- dorsoventrally flattened (greater surface area to respire by diffusion)
- tegument (surficial covering of a multicelular organism, an integument)
- parenchyma (loosely arranged mass of fibers and cells of several types)

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10
Q

Subclass: Digenea

A

Digenetic trematodes (flukes): a subclass within the class Trematoda
- digeneans parasitize all classes of vertebrates
- develops in at least two hosts
- first host is a mollusk (most often a gastropod) or very, rarely an annelid
Domain: Eukaryota
Kingdom: Animalia
Plylum: Platyhelminthes
Class: Turbellaria
Monogenea
Cestoidea
Trematoda
Subclass: Digenea
Aspidobothrea

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11
Q

Body Form

A

Most are dorsoventrally flattened and oval ni shape; others as thick as they are wide
- length ranges from 1.0 m to 6.0 cm

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12
Q

different suckers

A

Oral sucker: muscular sucker that surrounds the mouth
Acetabulum: ventral sucker of a fluke
Distome: fluke with two suckers, oral and ventral
Monostome: fluke that lacks a ventral sucker
Amphistome: fluke with the ventral sucker located at the posterior end

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13
Q

Tegument: surficial covering of a multicellular organism, an integument

A
  • distal cytoplasm: anucleate layer of cytoplasm above a “sunken epidermis”
  • cytons: cel bodies containing nuclei; lie beneath superficial muscle layer
  • internuncial processes: channels that connect cytons ot distal cytoplasm
  • syncytial: describes the continuous distal cytoplasm with no intervening cell membranes
  • spines: consist of crystalline actin; often present in certain areas of the tegument
    • spines lie above the basement membrane of distal cytoplasm
    • most flukes can absorb small molecules including amino acids and hexoses
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14
Q

Muscular system

A
  • circular muscles lies beneath the basal membrane of tegument
  • longitudinal and diagonal layers underlying the circular muscles envelop body - muscle fibers are smooth, often in syncytial clusters
  • myocyton: cell body of a muscle cell where nuclei occur; connect to fiber bundles
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15
Q

Nervous system: cerebral ganglia with orthogonal nervous system

A

orthogon: describes the ladderlike arrangement of nervous system in flatworms
- 3 main pairs of longitudinal trunks (dorsal, ventral, and lateral)
- cross-connected by a series of transverse commissures
- sensory endings extend from tegument; many types in cercaria and miracidium
tangoreceptors- receptors sensitive to touch
chemoreceptors- sensory receptor that responds ot chemical stimuli (some strikingly similar to olfactory receptors of vertebrate nasal epithelium)
eyespots: allows organism to distinguish light direction

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16
Q

Excretion: removal of waste takes place across tegument, epithelial lining of gut,
exocytosis of vesicles, and via excretory system

A
  • removal of waste products of metabolism
  • removal of unnecessary or harmful substances
  • regulation of internal osmotic pressure
  • regulation of internal ionic composition
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17
Q

Protonephridia

A

excretory system that is closed at the inner end by a flame cell and opens by a pore at the distal end

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18
Q

Flame bulb: specialized hollow excretory or osmoregulatory structure

A
  • one or several small cells containing a tuft of flagella
  • situated at the end of a minute tubule
  • connected tubules ultimately open to the outside
  • rod-like extensions of the flame cel form a filtering apparatus (weir)
  • ductules of flame cells join collecting ducts that eventually feed into an excretory bladder that opens outside through a single pore
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19
Q

Flame cell formula: represents the number and arrangement of flame cells

A

used as a taxonomic character

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20
Q

Flame cell formula Steps:

A

1 Draw a vertical line down the center from anterior to posterior end. 2[( )+( )]
2. Draw a horizontal line where the main
collecting ducts bifurcate.
3. Starting anteriorly from the upper quadrant count the number of flame cells in a common
cluster. Add this number to other number of
flame cells in the remaining cluster. 2[ (3+3+3) +()]
4. Repeat with the lower quadrant working from anterior to posterior.
2[(3+3+3) + (3+3+3)]

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21
Q

Digestion- digestion in most flukes is predominantly extracellular in the ceca
waste is expelled through

A
  • excretory system or tegument
  • stored in worm tightly bound to protein
  • periodically regurgitated
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22
Q

Cytokines

A
  1. cytokines are protein hormones utilized by immune cells to communicate
  2. can affect same cells that produce them, cells nearby, or cells distant in body
    Ex. interferon, interleukin, growth factors, etc.
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23
Q

Cell Signaling

A
  1. ligand binds to a specific cell receptor protein, initiating intracellular signal cascades
  2. ligands may be located on cell surface of neighboring cells, dissolved in blood (cytokines) or on the surface of or secreted by pathogens
  3. cascades may activate transcription factors or proteins that control gene induction, phagocytosis, apoptosis, or secretion
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24
Q

Cell Signaling

Ex. JAK-STAT pathway: 3 main components include

A
  1. receptor
  2. Janus Kinase (JAK)
  3. Signal Transducer and Activators of Transcription (STAT)
    1. transmembrane receptor, activated by cytokine
    2. activates the JAK protein, which adds phosphate groups (P) to the receptor
      -Kinases: are proteins that add phosphate groups to other proteins
      -Phosphate groups: act as “on” and “of” switches on proteins
    3. STAT is recruited and itself becomes phosphorylated, forms dimer, and moves into the cell nucleus, where it binds to DNA promoter region
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25
Pattern Recognition Receptors- receptors with broad specificity that bind to molecules on the surface of pathogens; stimulated by PAMPs - Pathogen-associated molecular patterns (PAMPs): small molecular motifs conserved within a class of pathogens
A. Scavenger receptors: bind lipoproteins and lipopolysaccharides from bacterial cells including Gram-positive bacteria (lipoteichoic acid) and Gram-negative bacteria (lipopolysaccharide) B. Complement receptors: integral membrane proteins that recognize fragments of complement and mediate various defense functions, including phagocytosis C. Toll-like receptors (TLRs): single, membrane-spanning, receptors that recognize structurally conserved molecules of carbohydrates, nucleotides, and proteins derived from viruses, bacteria, protozoa, and helminthes parasites
26
Four important aspects of immune response include:
1. nonself recognition: ability to distinguish self-antigens from nonself 2. antigen-specific: recognizes and is directed against specific antigens 3. systemic response: immunity is not restricted to initial infection site 4. "memory": recognizes and mounts stronger atack on previously encountered pathogens
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Basis of self and nonself recognition
Major histocompatibility complex (MHC): cell surface glycoproteins, highly polymorphic A. MHC class I proteins - presents in every nucleated cell of the body (few exceptions) -Cytotoxic T cells (CD8) respond to endogenous antigen bound to MHC class I proteins B. MHC class II proteins -found only on antigen presenting cells (macrophages, B cells, and dendritic cells) -TH cells (CD4) respond to exogenous antigen bound to MHC class II proteins
28
Different Ig
IgM: pentamer, 1st antibody secreted during primary immune response; monomer, present on surfaces of B cells IgG; monomer, major antibody secreted during the secondary response; 75% of plasma antibodies IgD: monomer, present only on surfaces of Bcells; serves as antigen receptor IgA: dimer, most abundant form of antibody in body secretions; high density of IgA-secreting plasma cels in MALT IgE: Fc binds to mast cells, basophils, etc.; often secreted in response to helminth worms; low conc. in plasma
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Plasma B cells: are large B cells that have been exposed to antigen
- produce and secrete large amounts of antibodies - short lived cells and undergo apoptosis when the inciting agent that induced immune response is eliminated
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Memory B cells: specific to antigen encountered during primary immune response
- can respond quickly following a second exposure to same antigen - long lived cells
31
Human immunodeficiency virus (HIV): a retrovirus that attacks the body's immune system; causes AIDS
A. HIV mounts direct attack on TH cells by binding to CD4 proteins on cell surface; monocytes are infected because they also express CD4 B. HIV kills TH cells, via apoptosis, faster than they can proliferate over time C. HIV-encoded proteins also cause a decrease in the expression of MHC class I on infected cells, so these cells are less likely to be recognized and are killed by NK cells D. when CD4+ Tcell numbers decline below a critical level of 200 cells per uL, cell-mediated immunity is lost
32
Acquisition of nutrients:
Feeding and digestion- varies with nutrient type and habitat within the host Ex. flukes of lungs, intestine, urinary bladder, rectum, and bile ducts draw a plug of tissue into their oral sucker and use pharynx as a pump to erode tissue Ex. flukes living in blood vessels are immersed in its semifluid blood food, so has no necessity ot breach host tissue
33
Reproductive system:
- most trematodes are hermaphrodites, and some can self-fertilize - always cross-fertilize if 2 or more digeneans are in the same host - exception are schistosomes that are dioecious - ectolecithal system: yolk is contributed by vitelline cells, yolk not stored in female gamete
34
Male Reproductive system:
testes: usually 2, number varies with species - each testis has a vas efferens that ultimately connects to vas deferens - internal seminal vesicle: located within cirrus pouch, stores sperm cirrus: male copulatory organ; cirrus pouch encloses the cirrus
35
Digenea: Form and Function Female Reproductive system:
ovicapt: sphincter muscle that controls the release of oocyte from the ovary Laurer's canal: vestigial vagina Mehlis' gland: unicellular mucous and serous glands surrounding the ootype ootype: a slightly expanded area of the oviduct that is surrounded by Mehlis' gland vitellaria: a group of vitelline glands that produce vitelline cells - vitelline cells produce the bulk of the shell material and yolk of the egg oogenotop: "egg forming apparatus"
36
Development
Polyembryony: development of a single zygote into more than one offspring - Somatic cell: contributes to body tissue of the embryo - Propagatory cell: stem cells - they are germinal cells in reproducing forms Ex. additional embryo in miracidium, sporocyst, or redia - give rise to germ cells in sexual adults Ex. sperm and egg
37
Pathogen: any organism or substance that produces a disease state
Pathogenicity: encompasses the total sum of consequences regarding the presence of a foreign species in the host - a parasite is pathogenic if it causes changes in hte anatomy, physiology or behavior of the host Virulence: deals with the consequences of the presence of the foreign species on the transmission of the hosts genes - a parasite is virulent if it reduces host reproductive success
38
Digenean: Leucochloridium variae
- definitive hosts include warblers - embryonated eggs are ingested by the terrestrial snail (Succinea ovalis) - sporocyst divided into 3 parts: 1. central body in snail's hepatopancreas 2. tube connecting the central body to the broodsac 3. broodsac in the head-foot of the snail and enters its tentacles - brightly colored broodsac pulses in enlarged snail tentacle - tailless cercariae develop in branched sporocysts; metacercaria encyst in broodsac
39
Digenean: Alaria americana
Parasite of wolves, foxes, coyotes, and the domestic dog (humans are accidental hosts) - miracidia hatch out of egg and penetrate snail - sporocysts shed cercariae - cercaria penetrate tadpole - mesocercaria develop in tadpole (infective to next host, either paratenic or definitive host) - water snake (paratenic host) eats infected tadpole or frog - canid eats infected snake and mesocercariae are freed by digestion - mesocercariae penetrate gut, move to diaphragm & then lungs (metacercaria) - (after 5 weeks) they migrate up the trachea and then to the small intestine
40
Alaria americana Pathology:
- mature Alaria sp. very pathogenic causing severe enteritis - often kills host in severe infections - can be fatal in humans when accumulated in large numbers
41
Alaria americana Epidemiology:
- found in various species of Canidae in northern North America - mesocercariae are pathogenic to human - acquired by eating undercooked frogs' legs - transmammary transmission of mesocercariae to offspring via milk
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Population structure:
set of quantitative descriptors of a host population, including prevalence of infection, incidence, abundance or density, intensity, variance of a frequency distribution, and curve of best fit
43
prevalence
percentage in individuals of a single host species infected at a given time
44
incidence
the number of new infections per unit time divided by the number of uninfected hosts at the beginning of the measured time
45
Abundance or density:
average number of parasites of one species per sample of host individuais of the same species, equal the arithmetic mean
46
Intensity:
the number of parasites of one species in an infected host
47
Mean intensity:
the average number of parasites of one species per infected hosts in a sample
48
Aggregated or overdispersed:
a situation in which most of the parasites occur in a relative minority of hosts and most host individuals are either uninfected or lightly infected
49
Parasite community:
the number of different parasite species infecting a single host individual
50
Macroepidemiology:
study of the effects of large scale factors, such as climate and culture, on distribution of disease in a population
51
Microepidemiology
study of the effects of small scale factors, such as parasite strains, host genetic variation, on distribution of disease in a population
52
Landscape epidemiology
approach of epidemiology that employs all ecological aspects of a nidus - by recognizing certain physical conditions, the epidemiologist can anticipate whether a disease can be expected to exist
53
Nidus
specific locality of a given disease; result of a unique combination of ecological factors that favors the maintenance and transmission of the disease organism
54
Digenean: Schistosoma spp.
Family: Schistosomatidae: have no 2nd intermediate host in their life cycles - mature in the blood vascular system of their definitive host - most species are dioecious Genus: Schistosoma: refers to the "split body" of the male considerable sexual dimorphism exists which include: - males have tegumental tubercles - males are shorter and stouter than females - males have a ventral longitudinal groove (gynecophoral canal)
55
Schistosomes host specificity
Schistosoma mansoni: found in the portal veins draining the large intestine - moderate host specificity - reservoir host include: rodents and monkeys Schistosoma haematobium: prefers the veins of the urinary bladder - most host specific (no known reservoir hosts) Schistosoma japonicum: more concentrated ni the veins of the small intestine - least host specific - reservoir hosts include: rodents, cats, dogs, pigs, cattle, horses, and deer
56
Digenean: Schistosomes Pathology
Migratory phase: time from penetration until schistosome is reproductively mature - often no symptoms or dermatitis reaction Actute phase (Katayama fever): occurs when schitosomes begin producing eggs - sufficient time and exposure has elapsed to elicit humoral response - egg production dramaticaly increases antigen release causing: chills, fever, fatigue, headache, malaise, muscle aches, GI discomfort etc. Chronic phase: S. mansoni- hepatic and pulmonary cirhosis, hepatosplenomegaly S. haematobium- bladder wall becomes ulcerated, bloody urine (hematuria) S. japonicum-hepatic and pulmonary cirhosis, hepatosplenomegaly; cerebral schistosomiasis
57
Digenean: Schistosomes Epidemiology
- Human waste water containing intermediate host is #1 empidemiological factor S. mansoni: broad distribution: Africa, Middle East, South America, and Caribbean S. japonicum: limited ot Japan, China, Taiwan, the Philippines, and Southeast Asia S. haematobium: limited ot Africa and adjacent regions - schistosomes may live 20 to 30 years - Schistosomiasis transmission has been reported from 78 countries - More than 75.3 million people were treated for schistosomiasis in 2021 - 200,000+ deaths per year Concomitant immunity: host is protected against new infections, but the parasite eliciting the immunity remains alive and unaffected
58
Digenean: Fasciola hepatica
Parasite of ruminants (cattle, goats, sheep, deer, etc.), and humans - adult parasite feeds on lining of bile ducts
59
Digenean: Fasciola hepatica Pathology
- much necrosis results from migration of flukes through liver parenchyma (2 months) - anemia sometimes results from heavy infections - worms in in bile ducts cause inflammation, edema, and stimulates fibrosis - migrating juveniles cause ulcers in ectopic locations: eyes, brain, skin, &lungs Ruminants - enormous losses in livestock because of mortality - reduction of milk and meat products; and especially spoiled livers - secondary bacterial infections - expensive anthelmintic treatment
60
Digenean: Fasciola hepatica Epidemiology
- can live as long as 11 years - infection begins when metacercarial cyst is ingested from water or vegetation - human often infected by eating watercress - sheep, cattle, goats and rabbits are most frequent reservoirs of infection in US - few human cases in US; most common in the South and West - human infections occur Europe, northern Africa, Cuba, South America, & other locales - WHO estimate 2.4 million persons were infected with fascioliasis worldwide in 2018
61
Digenean: Ribeiroia ondatrae
- national attention in 2007 regarding widespread reports of deformed amphibians - 1st intermediate host are various freshwater snails - 2nd intermediate hosts are fish and larval amphibians (frogs and salamanders) - large numbers of metacercariae encyst where hind limb buds form ni tadpoles - encysted metacercariae cause deformation of hind limbs - definitive hosts include herons, hawks, and badgers
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Digenean: Dicrocoelium dendriticum
- common ni the bile ducts of sheep, cattle, goats, deer, and pigs - no need for aquatic environment for any life cycle stages
63
Digenean: Dicrocoelium dendriticum Pathology
- conditions of dicrocoeliasis is similar to fascioliasis, but less severe - no trauma ot gut wall or liver parenchyma (no migrating juveniles) - chronic constipation, bile duct inflammation, fibrosis, and hepatocyte degeneration
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Digenean: Dicrocoelium dendriticum Epidemiology
- common throughout most of Europe, Asia, Africa, North and South America - acquired by accidental ingestion of ants on fresh herbs or vegetables
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Digenean: Clonorchis sinensis Pathology
- erosion of epithelium in larger bile ducts & main branches - inflammation becomes prominent, fibrosis, necrosis and atrophy of surrounding liver tissue - trapped eggs become surrounded by granulomas, interfering with liver function - eggs and sometimes entire worms become nuclei of gallstones - cancer of the bile duct si often associated with clonorchiasis
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Digenean: Clonorchis sinensis Epidemiology
-can live 8 years in humans - clonorchiasis is common in countries that eat raw fish - reservoir hosts include dogs, cats, pigs, and rats that contaminate streams - widely distributed in Japan, Korea, China, Taiwan, and Vietnam - eating frozen, dried, or pickled fish imported from endemic areas has caused infection - metacercariae wil withstand freezing, drying, pickling, salting, and smoking fish - may be futile to get milions of people to break century old habit - educating people to cook fish not option for many because fuel is luxury - fish farms contaminated with human feces ("night soil") used as fertilizer throughout much of Asia
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Digenean: Paragonimus westermani Pathology
- once in lung or ectopic site, worm stimulates an inflammatory response - parasite becomes enshrouded in a granuloma - eggs in surrounding tissues result in pseudotubercles - worms in spinal cord can cause paralysis - fatal cases are seen when Paragonimus spp. locate ni heart or brain - pulmonary cases are rarely fatal; chronic cough, breathing dificulty, sputum containing blood
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Digenean: Paragonimus westermani Epidemiology
- reservoir hosts often include felids, canids, rodents and pigs - worms can live 10 to 20 years - human become infected by eating raw or insuficiently cooked crustaceans - marination in brine, vinegar, or wine have no affect on metacercariae - exposure can also come from contaminated fingers and cooking utensils - some ethnic groups use of juices strained from crushed crab or crayfish for medicinal purposes (poultice) - variety of mammals and some birds can serve as paratenic hosts Ex. Guinea pigs: considered a delicacy in Ecuador and Peru
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Praziquantel (Biltricide)
- developed by Bayer and Merck in the mid 1970s - on the World Health Organization's List of Essential Medicines -drug of choice by CDC efective against: Alariasis, Clonorchiasis, Paragonimiasis, Dicrocoeliasis, Schistosomiasis, Dipylidiasis, Hymenolepiasis, Taeniasis - increases calcium ion permeability of membranes; induces contraction ¶lysis - available in the United States as Biltricide by Bayer 1( dose pack - 6 tablets - $105.00)
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Albendazole (Albenza)
- developed by SmithKline in 1972 - broad-spectrum anhelmintic - on the World Health Organization's List of Essential Medicines - alternative drug of choice by CDC efective against: Clonorchiasis - binds to colchicine-sensitive site of tubulin eliminating its polymerization into microtubules leading to impaired uptake of glucose - available in the United States as Albenza by GlaxoSmithKline 1( dose pack - 2tablets - $215.00)
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Triclabendazole (Egaten)
- on the World Health Organization's List of Essential Medicines - drug of choice by CDC efective against: Fascioliasis - binds ot beta-tubulin preventing the poymerization of microtubules leading to impaired uptake of glucose and depletion of glycogen - not available ni the United States, but is available through CDC
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Cestoidea Cestoidea: a class within the phylum Platyhelminthes
- monoecious parasites, hermaphrodites - acoelomate; no digestive system - adults live in the digestive tract of vertebrates
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Cestoidea anatomy
Scolex: "head" or holdfast organ of a tapeworm - may have suckers, grooves, hooks, spines, glands, or tenatacles - contains the neural ganglia of the worm Neck: an undifferentiated zone located between the scolex and the strobila - contains stem cells responsible for giving rise to new proglottid Strobila: region of tapeworm behind the scolex &neck; chain of proglottids Proglottid: a segment in a strobila that includes male &female reproductive organs -proglottid can copulate with itself, with others in its strobila; or with those in other worms, depending on the species
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proglottid type
Polyzoic: a strobila consisting of more than one proglottid Monozoic: tapeworm whose "strobila" consists of a single proglottid
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detaching proglottids
Strobilation: formation of a chain of proglottids by budding Gravid: a proglottid containing fuly developed eggs or shelled embryos Apolysis: disintegration or detachment of a gravid tapeworm segment Anapolysis (pseudoapolysis): detachment of senile proglottid after ti has shed its eggs Hyperapolysis: detachment of a proglottid while still immature, before eggs are formed - may lead an independent existence in the gut while maturing
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overlapping proglottids
Craspedote: posterior edge of each segment overlaps the anterior edge of next segment Acraspedote: posterior edge of proglottid does not overlap the anterior edge if the next
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scolex specifics
Acetabula: a sucker on the scolex of a tapeworm; normally 4 acetabula on a scolex Bothridia: usually in groups of 4;can have highly mobile, leaflike margins with adaptations for adhesion Rostellum: dome-shaped area on the apex of the scolex, often with hooks Bothria: usually 2 in number (dorsal and ventral), and take the form of shallow pits
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Microtriches: are numerous minute finger-shaped tubes that extend out of tegument
- increases the absorptive area of the tegument - completely cover the worm's surface - glycocalyx is found on the surface membrane of microtriches - below microtriches is a layer of distal cytoplasm
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Cestoidea: Form and Function Muscular system
- muscle cells consist of 2 portions: contractile myofibril and noncontractile myocyton - contractile portion contains actin and myosin fibrils, and it is nonstriated - myocytons comprise most of the cestodes parenchyma - bundles of longitudinal and circular muscle fibers lie below the distal cytoplasm - more powerful musculature lies below the superficial muscles
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Cestoidea Nervous system
-nervous system of cestoidea displays the orthogon plan typical of Plathyhelminthes -main nerve center is located in the scolex -innervation of ganglia, commissures, and motor and sensory neurons occur at the main nerve center, complexity often depends on complexity of scolex -sensory function most likely includes tactoreception and chemoreception
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Cestoidea: Form and Function Excretion and Osmoregulation
- main excretory canals run from the scolex to the posterior end of strobila - canals empty at the end of the strobila when terminal proglottids detach - excretory ducts are lined with microvilli - flame cell protonephridia provide motive force to the fluid in the system - end products of cestode energy metabolism are excreted through the tegument - osmoregulation is also function of tegument
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Cestoidea: Form and Function Reproductive system
- monoecious; few exceptions - in mature proglottid, sperm is transferred and oocytes are fertilized - usually male organs mature first, sperm is stored until maturation of the ovary Protandry (androgyny): maturation first of male gonads and then of females - in a few species the ovary matures first, known as protogyny - may be an adaptation that prevents self fertilization of the same proglottid - usually reproductive pores of both sexes open into a genital atrium
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Cestoidea: Form and Function Male
- one to many testes, each has vas efferens, unites into common vas deferens - sperm channeled toward the vaginal opening -cirrus pouch: amuscular sheath containing cirrus - the male copulatory organ is the muscular cirrus, which may have spines
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Cestoidea: Form and Function Female
- ovary and associated structures - the entire complex is known as the oogenotop - vitelline cells contribute yolk and shell material ot the embryo - oocytes leave ovary through the oviduct, which has a sphincter, or oocapt
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Cestoidea: Form and Function Development
(1) embryogenesis within the egg gives rise to larva (oncosphere - a six hooked larva hatched from an egg of a eucestode; also known as hexacanth) (2) oncosphere hatches and penetrates extraintestinal site (3) metamorphosis of the larva into a juvenile (metacestode) in extraintestinal site (4) metacestode develops into adult in the intestine
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Diphyllobothrium latum
- broad fish tapeworm - occurs ni humans, bears, cats, dogs, and other fish-eating carnivores - adults live in small intestine - 10 meters length; >4,000 proglottids; sheds 1million eggs per day - eggs released through uterine pore
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Diphyllobothrium latum pathology
- pernicious anemia; large amount of B12 absorbed by tapeworm - Sparganosis: infectious disease caused by migrating plerocercoids in host tissues - can reach 35cm in length; can live for at least 30 years (1) swallowing procercoid-infected copepods in drinking water (2) eating amphibians, reptiles, and mammals containing plerocercoids (3) applying plerocercoid-infected flesh to wounds as a poultice
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Pseudophyllidea: Diphyllobothrium latum Epidemiology
-eating undercooked freshwater fish - accidental ingestion of copepod from unfiltered water - insufficiently cooked frog, snake, or pig - poulticing inflamed area or wound with split frog
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Cyclophyllidea: Taenia saginata
- beef tapeworm - occurs in humans in countries where beef is eaten - 3to 5meters length; >2,000 proglottids - adult beef tapeworm lives in small intestine - gravid segments detach and pass out with feces or migrate out of anus - proglottid begins to dry and ruptures, thus releasing eggs - larvae (hexacanth) remain viable for weeks
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Cyclophyllidea: Taenia saginata Pathology
- may be asymptomatic - symptoms of dizziness, headache, abdominal pain, diarrhea, and nausea - intestinal obstruction with need for surgical intervention sometimes occurs - loss of appetite is not frequent - - delirium is rare
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Cyclophyllidea: Taenia saginata Epidemiology
- infection is highest where beef is a major food and sanitation is deficient - one person who defecates in pasture can infect entire herd - use of human feces as fertilizer (night soil) - cattle are coprophagous
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Cyclophyllidea: Taenia solium
-pork tapeworm - most dangerous adult tapeworm to humans - humans can serve as definitive and intermediate host - life cycle same as beef tapeworm except the normal intermediate host is pig - humans become an intermediate host when the eggs are accidentally ingested or agravid proglotid ruptures releasing eggs before it leaves the body - humans become a definitive host when ingesting cysticerci in undercooked pork
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Cyclophyllidea: Taenia solium Pathology
- cysticerci can be found in any organ and tissue including: (1) subcutaneous connective tissues (2) eye (3) brain (epilepsy, blindness, paralysis, disequilibrium, disorientation, etc.) (4) muscles (5) heart (6) liver (7) lungs (8) coelom
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Cyclophyllidea: Taenia solium Epidemiology
- infection is highest where pork is a major food and sanitation is deficient - eggs can be transmitted by Blowflies - infected (domestic help) person can contaminate households or food Ex. 1.3% Orthodox Jewish community ni New York infected by T. solium N Engl J Med. 1992 Sep 3;327(10):692-5. - cysticercosis is highly endemic in Mexico, Central and much of South America, sub-Saharn Africa, India, China, and other parts of eastern Asia
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Cyclophyllidea: Echinococcus granulosus
- adults are in small intestine of carnivores, particularly dogs and other canines - herbivores (intermediate host) are infected by eating eggs on contaminated herbage - within liver or lungs oncosphere metamorphoses into unilocular hydatid slyvatic cycle: life cycles that involve wild animals Ex. (wolf-moose, lion-warthog, etc.) urban or domestic cycle: life cycles that involve rats and domesticated animals Ex. (dog-sheep, dog-goat, dog-pig, etc.
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Cyclophyllidea: Echinococcus granulosus Pathology
- hydatid cyst can occur ni any organ: liver, lungs, brain, etc. - type and extent of pathology depends on cyst size and location - as cyst size increases it crowds adjacent tissues and organs interfering with function - cyst can become enormous: > 3 gallons of fluid, millions of protoscolices - release of hydatid fluid may cause anaphylactic shock
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hydatid cyst
- hydatid has thick outer noncellular layer and thin inner nucleated germinal layer - brood capsules on inner layer of hydatid, each capsule has 10-30 protoscolices - brood capsules within hydatid break down and release "hydatid sand"
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Cyclophyllidea: Echinococcus granulosus Epidemiology
- human becomes infected when they accidentally ingest egg when playing with dog - some tribes in Kenya relish dog intestine roasted on a stick - some tanners in Lebanon use dog scats as ingredient of a solution for tanning leather - echinococcosis disease can be eliminated in infected areas by the following: (1) general educational program (2) denying access of dogs to offal (3) destroying stray dogs
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Cyclophyllidea: Echinococcus multilocularis
- adult E. multilocularis mainly found in foxes - dogs, cats, and coyotes can also serve as definitive hosts - several species of rodent serve as intermediate host: mice, rats, voles, lemmings - E. multilocularis metacestode is alveolar or multilocular hydatid
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alveolar cyst
-has thin wall and germinal epithelium - may bud externally and spread in any direction or even metastasize
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Cyclophyllidea: Hymenolepis nana
- dwarf tapeworm (4 cm) - one of the most common cestodes of humans - intermediate host is optional (can develop normally in larval and adult beetles) - human or rodent ingests egg, oncoshpere hatches out of egg in duodenum - oncosphere penetrates mucosa and develops into cysticercoid (metacestode) - within 6 days cysticercoid return to lumen of small intestine to attach and mature
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Cyclophyllidea: Hymenolepis nana Pathology
- light infections are asymptomatic - heavy infections can occur because of autoinfection - symptoms are similar to those previously mentioned for Taenia saginata
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Cyclophyllidea: Hymenolepis nana Epidemiology
- more than 20 million people infected worldwide - prevalence of infection is highest for small children; ingestion of eggs - ingestion of grain products contaminated with infected insects (flour beetles) - rodent control measures and protection from their droppings
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Cyclophyllidea: Hymenolepis diminuta
- much larger than H. nana (90 cm) - common in rats; human infections not common - completion of lifecycle requires an arthropod intermediate host ( > 90 insect species) - other life cycle characteristics similar to H. nana
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Cyclophyllidea: Hymenolepis diminuta Pathology
- most infections are asymptomatic - some symptoms may include nausea, abdominal pains, diarrhea, and anorexia
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Cyclophyllidea: Hymenolepis diminuta Epidemiology
- primarily a zoonosis: a disease of animals transferable to humans - rodent control measures to prevent insect consumption of their droppings - protection from insects of cereals, grains or other non-cooked foods
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Cyclophyllidea: Dipylidium caninum
- common parasite of dogs and cats all over the world; often occurs in children - adult worms found in the small intestine - gravid proglottids detach and either wander out of anus or is passed with feces - when detached segment desiccates, egg capsules are released
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Cyclophyllidea: Dipylidium caninum Pathology
- light infections are often asymptomatic - some individuals experience abdominal pain, diarrhea, and anal itching
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Cyclophyllidea: Dipylidium caninum Epidemiology
- most likely to occur in small children who kiss or are licked by infected pet - periodic deworming of infected dogs and cats and control of fleas is essential
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Niclosamide
- on the World Health Organization’s List of Essential Medicines - used specifically to treat cestode infections - alternative drug of choice by CDC effective against: Dipylidiasis, and Taeniasis - uncouples oxidative phosphorylation severely limiting ATP production - not available in the United States