term 3 pos

what is PGE characterised by

• diarrhoea/ weight loss

• poor weight gain

• hypoalbuminaemia

examples of parasitic nematode worms casusing bovine pge

• ostertagia (abomasum)

• cooperia and neatodrus (small intestine)

life cycle of ostertagia

• adult ostertaga in abomasum

• egg containing L1 larva passed in faeces

• eggs hatch on pasture

• develops to L3 larva, migrates from faeces to grass

• L3 larva ingested by cow

• this L1 to L3 development is temperature dependent. it takes up to 2 weeks or can be even slower

• the prepatent period is 3 weeks, or up to 6 months if the development is arrested

• typical strongyle eggs in faeces: oval, thin clear wall, bundle of cells. 80um

• 3rd stage larva is 750 um.

• adult around 1cm long, brown. they emerge from the gastric glands and live/mate on abomasal mucosal surface

pathogenesis

• where do larvae migrate to on ingestion

• when do adult worms emerge

• what happens if a large number of worms emerge at the same time

• on ingestion larvae migrate to gastric glands of abomasum to continue development

• adult worms emerge from glands around 18 days later

• if a large number of worms emerge at the same time

  • pH increases from 2-7 as less acid produced as gastric glands are affected

  • pepsinogen cannot be activated to pepsin

  • abomasal epithelium becomes leaky

  • plasma proteins lost into gut lumen causing hypoalbuminaemia, weight loss and diarrhoea

what can happen to gastric mucosa

• thickened, hyperpastic

• raised nodules

• some of the L3 larvae survive on pasture overwinter

• the new eggs deposited in early spring develop slowly to L3 as it is too cold

• as the weather warms some existing L3 die as drier conditions and trapped in cow pats. but rate of L1 to L3 dev increases.

• Then L3 increase furthe as more calves are infected and shed and eggs in faeces

what does rate of infection depend on?

• host appetite

• number of infective larvae (L3) on pasture

• so disease is most common in calves where they are grazing permanent pasture and kept at a high stocking density

what happens to L3 is ingested in late autumn or early winter?

• L4 arrest in gastric glands

• then L4 resume development and emerge from glands in waves (type 2 disease)

immunity to ostertagia

• slow to develop - takes the whole grazig season

• may dip over winter ad re established upon turnot (2nd grazing season)

• adult cattle solidly immune

epidemiology in beef herds- spring calving

• calves at foot with cows

• spring mortality of L3 occurs before calves eat much grass

• so immun cows eat most of grass and pass few eggs

• so very low disease risk

epidemiology in autumn calving

• calves turned out at start of year and will eat some outwintered L3 BUT cows eat most

• then lower autoinfection peak

• some risk but still low

type i disease in cows

• typically calves in first grazing season

  • mid july onwards

• morbidity high, mortality low

• diarhoea common (larval damage to gastric glands)

• weight loss

type ii disease

• typically yearlings

• late winter/ spring following first grazing seasn

• prevalence low, only some affected

• mortality more likey

• ± diarrhoea with anorexia and thirst

• hypoalbuminea more marked, weight loss

control of type i disease

• use clean pasture

• delay turnout untul after spring mortality in L3

• strategic anthelmintic use

anthelmintic use

• macrocyclic lactone wormers last 5 weeks eg doramectin

• prepatent period for ostetagia s 3 weeks

• so dosing needed every 8 weeks

options

• dose and move to fresh pasture in july before autoinfection peak

  • but can still get disease if L3 high, increased risk of spreading resstant worms to fresh pastur

• dose every 8 weeks from july and keep on same pasture

• dose at spring turnout and 8 weeks later reducing autoinfection peak

• give an intraruminal device before turnout which reduces autoinfection peak

control of type ii

• cattle exposed to low challenge at pasture in late autumn

  • unlikely to require worming treatment at housing

• cattle exposed to medium/ high challenge at pasture in late autumn or cattle of unknown origin

  • likely to require worming treatment at housing

skin and problems

• thick layer of cells and sebaceous gland secretions

• wounds

• vector borne pathogens

mucous membraness

• mucociliary escalator, peristalsis

• coughing and sneezing, vomiting and diarrhoea

• secretions- physical and anti microbial properties

• commensal microflora

what does the innate immune sstem use for detection

• uses pattern recognition receptors to detect microbial components that are itrinsically foregin

  • protein associated molecular patterns eg

  • lipopolysaccharide in gram negative

  • peptidoglycan in gram positive

  • mannose sugar in prokaryotic carbohydrate molecules

bacterial PAMPs

pathogen associated molecular patterns

pattern recognition receptor

• where can they be found

• what type in each

• can be found in the cytoplasm, cell membrane, inside vessicles or as soluble molecules int he tissue fluid/plasma to detect PAMPS

• cytoplasm: NOD receptors

• membrane bound: TLRs

• soluble: complement c3 protein, mannose binding lectin, c reactive protein

toll like receptors- what do these recognise

• 2

• 4

• 3 and 7

• what are they predominantly expressed by

• tlr2 recognises peptidoglycan- gram positive

• tlr 4 recognises LPS - gram negative

• tlr3 and 7 recognise viral nucleic acid

• predominantly expressed by neutrophils and macrophages

how does innate to viral work

• how are they detected

• how do cells respond and what effect does this have

• do not have strutural pamps

• are detected by presence of double stranded rna produced during replication (not present in mammalian cells) or DNA in the cytoplasm

• cells respond by producing type 1 interferon

  • this includes interferon alpha, beta, omega

  • interferons have a paracrine effect

function of type 1 interferon

• resistance to viral replication

• act on neighbouring

  • increased deradeation of viral mrna

  • inhibition of viral protein sythesis

  • increased antigen presentation of viral antigens

what is the paracrine effect

innate immunity to viruse

• viruses can infect any nucleated cells

• all nucleated cells can respond to viral infection by producing type 1 interferon

• interferon omega can be used to treat persistent viral ifnection of cat eg FeLV/FIV

natural killer cell- large granular lymphocyte

• what does it recognise

• what does it release

• recognise decreased levels of MHC molecules on host cells

  • there is decreased production during viral protein synthesis

  • some virus block transport to cell surface to prevent expression

• this decrease is a symptom of viral infection.

• the NK cell releases toxic granules killing the cell before the viral replication is complete

innate- cellular mechanisms

• what is the response

• how is the micro organism killed

• what helps and enhances

• recognition of pathogen (membrane, vesicular and cytoplasmic PRR)

• response is phagocytosis and inflammation

  • phagocytic organisms attach to the organism and use pseudopodia to capture it forming a phagosome

  • then it stimulates a respiratory burst and toxic metabolites (eg oxygen free radials, hydrogen peroxide) are pumped into the vesicles to kill the micro organism

  • subsequent fusion of the lysosomes with the phagosome (phagolysosome) releases proteolytic enzymes and anti microbial mediators (defensins and lactoferrin)

  • increasingly acidic pH results in digestion of the microorganism

  • enhanced phagocytosis (opsonisation) can be achieved with the help of the antibody IgG and or complement CC3b

  • destruction of endocytosed organisms can be enhanced by stimulation of cytokines released by T helper cells

innate- humoral mechanisms

• recognition of pathogen- soluble PRR

• response: killing of foreign organism, enhacned phagocytosis and inflammation

tlr

what could NOD2 receptor defect cause

• crohns in man

• ibd or anal furunculosis in german shepherd

what does recogn tiion of bacteria by macrophage tlr lead to

phagocytosis and inflammatory resposne

respiratory burst

• what is it

• what is formed

• enhanced cellular aeorbic metabolism

• reactive oxygen intermediates are formed

  • superoxide anion

  • hydroxyl radicals

  • hydrogen peroxide

• this isthe oxygen dependednt mechanism of bacteiral killing

lysosomes

• 3 types

defensins

• cationic anti microial peptides that damage bacterial cell wall

lactoferrin

• binds and chelates free iron, which is required for bacteiral growth

acid proteases

• digestive enzymes active at low pH

inflammatory mediators-histamine

• what is it released by

• produced by mast cell degranulation in tissues

• anti histamine

pro inflammatory cytokines

• examples

• what are they synthesised by

• tumour necrosis factor a

• synthesised predominantly by wbc and macrophages

• corticosteroids

lipid mediators of inflammation

• prostaglandin and leukotrienes

• derived from arachidonic acid by action of cycloocygenase and lypoxygenase enzyme

• nsaid

localised effect

inflammation

systemic

hypothalamus

• fever

liver

• acute phase response

bone marrow

• neutrophil and monocyte mobilisation

• speed up production

acute phase response

• where are the proteins produced by in response to what

• examples

• what do they do

• are they specific or non

• acute phase proteins are produced by the liver in response to pro inflammatory cytokines

• serum amyloid protein, C reactive protein and mannose binding lectin stick to bacterial cell walls

  • act as opsonins to enhance phagocytosis and stimulating complement activation

• but are non specific

complement

• where are complement proteins found

• what steps do they form

• what is the end product

• complement prtoens are found in the blood

• series of enzyme activation steps forming an aomplification cascade

• small amount of activation is amplified to generate a large response

• similar in nature to clotting cascade but with a diff trigger and outcom

• the end product of the cascade is the polymerisation of C9 monomers to form a C9 polymer forming a membrane attack complex

  • a tube like structure that create holes in the cell walls of bacteria causing them to lyse

• inactive C3 in the blood dissociates into C3a and b in the presence of bactiera- it is a pro enzyme

  • C3b is deposited onto the surface of the microbe and acts as an enyzyme to catalyse the formation of the MAC and also act as an opsonin (phagocytic cells express c3b receptor)

  • C3a binds to receptors on local tissue mast cells triggering degranulation and stimuating a inflammatory response

what are 3 examples of physical barriers

• thick stratified squamous epithelium (skin and lower urinary tract)

• mucociliary escalator (resp tract)

• peristalsis, vomiting and diarrhoea when necessary (alimentary)

example of biochemical barriers

• lactic and fatty acis in sebum from sebaceous glands of skin

• enzyes

• acid in stomach

• antibacterial peptides eg defensin

how do commensal organisms provide protection

compete with organisms for space

provide natural antibiotic

what do gamma delta t cells do

react to stress proteins that are upregulated on the surface of infected mucosal epithelial cells

overall oucome of complement activation

• lysis of the bacteria by the MAC

• enhacend phagoytosis of bacteria coated in complement proteins C3b

• inflammation at the site of complement activation C3a

where are these prrs located

• TLR 2

• TLR 4

• TLR 5

• TLR 9

• NOD2

• peptidoglycan

• lipolysaccharide

• flagellin

• prokaryotic DNA

• muramyl dipeptide

localised efects of inflammatory cytokines

• vasodilation

• increased capillary permeability

• recruitment and influx of white blood cells

immunohistochemistry

• prepare cells in tissue

• apply a specific antibody against a target eg virus antigen

• anibody chemically modified to have enzyme to form antibody-enzyme conjugate

• wash the slide to get rid of unbound antibody

• add DAB substrate- colourless which changes to brown ppt with presence of enzyme

• look under microscope to find positive

Fluoresecent antibody test

• antibody is labelled with a fluorophore

• can see antibody binding to the target under a fluorescence microscope

enzyme linked immuoabsorbent assay

• can be used to detect either antigen or antibody

• if testing early test for antigen at site of infection, will still be in lag phase

• if testin more than 5 days post exposure test for antibody in serum (LOG phase) and retest 2-3 weeks later (plateau phase)

sandwich elisa method

• elisa plate

• add a specifc capture antibdy at the bottom which binds

• add in antigen in sample whch bins to antibody

• add another antibody which is also specific. this has een chemically modified with enyme

• add substrate—>colour change

elisa method for detection of antibody in serum

• add antigen at bottom

• add take blood sample and serum

• if anitbody present it will bind to antigen

• add a secondary antiboy (conjugate)

• colourchange

haemolytic bacteria

• produces a toxin that damages cells

  • does NOT cause haemolysis ad anaemia

• can test for this by culturing samples on sheep blood agar where haemolysis can be observed in the petri dish

• these pathogens will produce the same toxin at the site of infection causing damage to the local cells

titre definition in serology

the greatest dilution of serum that still gives a positive result for the presence of antibodies in the test

bacteria vs virus culture

• bacteria need nutrient agar at 37

• viruses require cells

  • need to culture cells in the lab that the virus is able to infect and replicate within

  • species specificity and tissue tropism will dictate the cll type rquired for virus isolation

opportunistic pathogen

a pathogen which does not normally cause disease but does when the hosts immune system is compromised

fluorescent antibody test

where can the pathogen be

• epithelial tissue

• cytoplasm

• tissue fluid

• vesicle- endosome

innate

• what receptors are involved

• specificity

• oldest

• tries to keep foregin out

• if organism breach external barriers recognise that infection is present and respond quick

• pattern recognition receptors

  • neutrophils and tissue macrophages target bacteria

  • eosinophils and tissue mast cells target parsites

• recognition of commonmicrobial molecules that are intrinsically foregineg peptidocycan of bacteria cell wall

• receptors for these are broadly reactive but not very specific

pathogen associated molecularpttens

• lipopolysaccharide= gram -ve

• peptidoglycan= gram positive

• viruses do not have obvious pamps

• some bacteria produce capsules to hide them

• innate immunity is no longer sufficient to protect thehost from all infections

• we need another strategy- adaptive immunity

adaptive

• immune resposne of higher species

  • much more efficient but slower to react

  • helps innate immune mechanism to work better

• anitgen receptors are expressed by lymphocytes- recognition of foregin antigens and have a highly specifc detection systems

• lymphocytes- t and b cells

• primary role in dealing with viruses

• also hep the cells of innate immunity to fight bacterial and parasite infections

what is an antigen

• usually a structural protein of a pathogen eg a spike protein

• lymphocyte receptors recognise the shape of a small region of the antigen

• this is the epitope

lymphocyte family tree

b cell receptor

• bind to whole antigen on the surface of a pathogen in the ecf

t cell

• recognises digestedantigen displayed ont he surface of other cell

  • proten is degraed to peptides

  • peptides are displayed on surface of cell hich cna be recognised by tcr

immunological synapse

when an immune cell creates contact with an antigen

lymphocyte development

• when a lymphocyte develops in the bone marrow it has to design its own unique antogen receptor

• they juggle their genes to generate a large amoutn of diversity

• constant and variable with antigenic epitope

clonal selection

what do b cells do

produce antibody eg immunoglobulin, gamma globulin which stick to pathogens

what do cd4 helper cells do

produce cytokines which activate other cells

cd8 killer cells

seek and destroy virus infected cells

b cells resposne to infection

• rcognition of antigen on surface of pathogen

• clonal epansion

• differentiation to plasma

• produciton to anitbody

antibody

• what are they

• what do they do once bound

• what are they secreted by

• where are they secreted and why

• antigen binding protiens

• soluble versions of the b cell surface antigen receptor

• targets the external surface of the pthogen

• once bound

  • inactivate/neutralise

  • attract phagocytic cells

  • triggers innate killing response

• secreted by plasma cells (drived from B)

• secreted into the lymph node where they can bind to their specific antigen in the ECF- cannot cross cell membrane

CD4+T lymphocyte

• are helper t cells

• some make cytokines to activat emacrophaces

• some make cytokines to assist b cells in making antibodies- B cell growth fators

CD8+T lymphocyte

• killer t cells

• kills infected

immunological memory

• after recovery we are left with an expanded population of lymphocyte clones

• these memory lymphocytes have a long lifespan

• immune syste respond much mor quixkly and efficiently

• instead of becoming effector cells they become quiescent

detection of infection

• some structures are intrinsically foreign eg lipopolysaccharide and peptidoglycan and pattern recognition receptors have evolved for their detection

  • typically found on the surface of wbc for detection of infection in the extraceluular fluid or in the cytoplasm for detection of infection i the intracllular fluid

• adaptive detects protein structure and shape to differentiate between self and foreign

  • lymphocytes express receptors on their surface that are designed to recogn ise foreign proteins bvy shape (antigens)

lymphocyte development

• a large number of diversity is generated by random juggling of receptor variable genes ton produce a receptor nprotein

• so each lymphocyte expresses uniquely shaped antigen receptor

• once designed, each lymphocyte will express many copies of its antigen receptor

B vs t

• the B cell antigen receptor is designed to detect epitopes of the whole antogen on the surface of pathogens located in the extracellular fluid

• the t cell receptor is designed to recognise fragments of digested antigen eg peptides that are displayed on the surface of other cells in association wiht specialist antigen presenting molecules -MHC

what is clonal selection

• during an infection, when a host is exposed to foreign antigen, only a small number of specific lymphocytes will react

• must proliferate to generate many copies

• usually occurs in the lymph nodes

what are parasites killed by

toxic mediators released by eosnopils and mast cells when they degranulate

how are viruses killed

a coordinated attack by lymphocytes by the acion of antibody and killer T cell

antibodies

erythrocytes

platelet

neutrophil

eosinophil

lymphocyte

monocyte

basophil

erythryocyte and leukocyte staining

• cytoplasm of erythryoctres stains pink

• that of leukocytes is blue grey with cytoplasmic granules staining grey/pink, red/pink or blue/purple

what do neutrophils, eosinophils and basophils contain in their cytoplasm

granules

in which cells are the nuclei lobed

neutrophils, eosinophils and basophils