FD6 PBL Flashcards
Describe the properties of Listeria monocytogenes
- small
- motile
- gram +ve
- nonsporeforming
- extremely resistant
- diphtheroid coccobacillus
- grows under a wide temp range (4-44 degrees)
- Ubiquitous saprophyte- lives in plant soil enviro
Why is its ability to grow at 4 degrees important?
- important diagnostic aid
- cold enrichment method - isolation of the organism from brain tissue but not from placental or fetal tissues
What are the natural reservoirs of L.monocytogenes?
- soil
- mammalian GI tracts
- both contaminate vegetation
How does animal-animal transmission of Listeria occur?
- via fecal-oral route
- through abrasions in the buccal cavity (dry pasture)
When is Listeria most prominent?
- primarily a winter-spring disease of feedlot/ housed ruminants
When do outbreaks of Listeria normally occur after feeding poor-quality silage
- over 10 days after
- (4-6 weeks)
Which animals to L.monocytogenes affect?
- sheep
- cattle
- humans
What is the incubation period of Listeria?
- 3-70 days
What is this? and why
- Listeria
- small, gram +ve rods
- sometimes arranged in short chains
- can be mistaken for strepococci
Which temp is lethal to L.monocytogenes?
50 degrees
What pH range will Listeria grow in?
- pH 4-9.6
Does Listeria grow better in aerobic or anaerobic conditions?
- anaerobic
What is the relationship between silage and Listeria?
- listeria can survive up to 3 months in livestock manure
- silage may become a source of infection if soil containing Listeria is included
- improperly prepared silage (pH >5.4), prelonged, slow exposure to air (secondary fermentation)- allows organism to multiply
- high levels of iron
- poorly stored silage can be contaminated with vermin
- close grazing with soil ingestion also can be a cause
What is the best way to prevent silage becoming a source of Listeria infection?
- well compacted silage
- cover immediatley after harvest
- well wrapped
- produce intensively fermented silages and store for over 30 days
- acid additive to wet silages
Why are the advantages of feeding silage?
- faster forage preserving methods
- high quality
- lower loss when harvesting, storing and feeding
- inexpensive to store
- wide seasonal harvesting window
- doesnt need to be fed fresh
- cheaper
How does Listeria reach the brain?
- L.monocytogenes travel by way of circulating blood,
- enters nerve fibres, primarily trigeminal nerve/ facial nerve and is transported to the brain stem
- the nuclei 5th and 7th are in the caudal brain stem
What can Listeria cause in general?
- septicemia
- abortion
- latent infection
What are the clinical signs in animals with Listeria?
- initially:
- anorectic
- depressed
- dioriented
- propel themselves into corners
- lean against walls
- circling toward affected side
- facial paralysis, drooping ear
- deviated muzzle
- flaccid lip
- lack of menace response
- continous salivation
- paralysis of masticatory muscle
- terminally affected animals:
- recumbancy and death
What is the recovery rate in goats/ sheep?
- 30% with prompt, aggressive therapy
Recovery rate of Listeria in cattle?
- 50%
When do Listeric abortions occur?
- last trimester without premonitory signs
- fetuses normally die in utero
- rate may reach 20% in flocks
How long can Listeria be shed in milk/ via vagina?
- > 1 month
Where do Listeria infections acquired via ingestion tend to localize?
- in intestinal wall
- results in prolonged fecal excretion
Describe the virulence and infectivity of Listeria
- L.monocytogenes ingested
- may survive the stomach enviro and enter intestine where it penetrates the intestinal ep cells
- the organism is taken up by macrophages and non-phagocytic cells
- L.monocytogenes surface protein interalin required for the uptake by non-phagocytic cells (binds to receptors on host cells)
- bacterium initially located in vacuole after uptake
- L.monocytogenes secrete listeriolysin O protein (breaks down vacuole wall and enables bacteria to escape into cytoplasm)
- L.monocytogenes replicate in cytoplasm
- then transported around the body by blood, most being inactivated with reaching liver/ spleen
- L.monocytogenes able to utilise actin molecules of the host to propel the bacteria into neighbouring host cells
- cross blood-brain barrier and placental barrier
In listeric encephalitis, where are microcropic lesions confined to?
- pons
- medulla oblongata
- anterior spinal cord
What lesions would be found in an animal with septicemic listeriosis?
- small necrotic foci in any organ, esp liver
- haemorrhagic gastroenteritis
What could be seen in aborted fetuses? (Listeria)
- slight to marked autolysis
- clear to blood-tinged fluid in the serous cavities
- numeroud small necrotic foci in the liver (esp right half)
- necrotic foci may be found in lungs/spleen
- shallow erosions, 1-3mm, may be present in abomasal mucosa
- autolytic changes may mask these lesions
Describe the placental lesions seen in Listeria
- severr diffuse necrotizing and supprative placentitis ofboth the cotyledons and the inter cotyledonary
- aborted foetus - multiple 1mm yellow/ white foci in many organs, large numbers in liver
- these foci are areas of acute necrotising hepatitis in which the gram +ve listeria microbes are numerous
- these lesions identical to campylobacteriosis and brucellosis (except the trophoblasts)
What are the differential diagnosis of Listeria?
- toxaemia (last 4 wks of pregnancy)
- brain abscesses
- peripheral vestibular lesions (middle ear infections)
- Gid (tapeworm cyst in brain)
How do you test for Listeria?
- isolate L.monocytogenes from the placenta, foetus or uterine discharges after an abortion
- blood/ CSF can be cultured in animals with septicaemia/ encephalitis
- at necropsy, the liver, kidneys and spleen can be cultured in septicaemic animals/ pons, medulla with encephalitis
- L.monocytogenes isolated from nasal discharges, urine, faeces or milk
How is Listeria cultured?
- samples directly plated on blood agar and simultaneously cultured with a cold enrichment procedure
- growth may take 3 months
- use biochemical tests to identify colonies
What is the difference in CSF in an animal with Listeria?
- increased protein content and mild pleocytosis composed of large mononuclear cells
How can Listeriosis be differentiated from pregnancy toxemia or ketosis in cattle?
- careful clinical examination
- CSF changes
- 3-OH butyrate concs well below 3mmol/L
- and facial/ ear paralysis absent in preg toxaemia and ketosis
What tests are used to identify presence of Listeria?
- use rabbit polyclonal anti-Listeria antiserum
- peroxidase-antiperoxidase technique
- ELISAs
- immunoflurescence
- immunochromatography
- immunomagnetic separation
- PCR
Why isnt serology used for diagnosis?
- many healthy animals have high Listeria titers
What is the human risk of Listeriosis?
- aborted foetuses and necropsy of septicemic animals- greatest hazard
- L.monocytogenes confined to brain
- people have developed fatal meningitis, septicemia, and papular exanthema on arms
- pregnant women:
- danger to foetus
- possible abortion
- stillbirth
- infection of neonates
- most infections are caused by eating the bacteria in food, or by aerosol/ direct contact
- spread indirectly via milk, cheese, meat, eggs, or veg
How do you treat Listeriosis?
- need early, aggressive antibiotic treatment
- penicillin (drug of choice)
- ceftiofur
- erythromycin
- trimethoprim/sulfonamide
- high doses - difficult in achieving minimum bactericidal concs in brain
- in heavily pregnant ewes - propylene glycol and rehydration therapies
- poor prognosis in sheep
- treatment only initated if not recumbent
What dosage of penicillin G should be given?
- 44,000 U/kg body wt, IM, daily for 1-2 weeks
- +fluid and electrolytes
How is silage made?
- silage must be made from plant material with a suitable moisture content (50-60%)
- undegoes anerobic fermentation, which starts about 48 hrs after silo is filled and converts sugars to acids
- completed after 2 wks
How are sweet and sour silages made?
- Sour:
- when silage is closely packed- the suppy of oxygen is limited and acid fermentation casues decomp of the carbs into acetic, butyric, lactic acids
- Sweet:
- if silage is unchaffed and loosely packed/ silo is built gradually, oxidation proceeds more rapidly and temp rises
- if the mass is compressed when the temp is 60-71 degrees, fermentation stops
Outline the steps of silage making?
- Pre-sealing-
- enables some resp and some dry matter loss
- Fermentation-
- occurs over a few weeks,
- pH drops
- more DM loss
- hemicellulose broken down
- aerobic resp stops
- Infiltration-
- some oxygen filtration
- limited micriobial resp
- CHOs lost
- Emptying
What type of silageis least conductive to listeria growth?
- silage that is compacted (anaerobic fermentation)
- pH of under 4.5
- has no incorporated soil
Optimum conditions for listeria?
- temp: 1-45 degrees/ optimum = 30-37
- pH - 4.5- 9.6
- anerobic and microaerobic conditions
How should the diet of a pregnant ewe be managed?
- in late pregnancy ewe appetite reduces by 30% due to lambs taking up more space
- increase nutrient density
- good quality silage supplies most nutrients needed but a source of DUP
- ewes with twins - BCS 3.3 by lambing
- ewes with single - BCS 2.8+ by lambing
- floor feeding - good so they have access to enough feed
What does Campylobacter result in?
- late abortion/ stillbirths
- easily spread by poor hygiene
- bacteria commonly found in sheep dung or abortion material
How does Toxoplasma result in abortion?
- parasite
- spread by infected cats defecating on sheeps feed
- parasite uses sheep as an intermediate host and causes them to abort in late pregnancy or absorb the foetus if infected early in pregnancy
What is the result of Enzootic abortion (EAE)?
- caused by the bacteria Chlamydophila abortus
- abortion occurs in last 2-3 wks of pregnancy
- once infected ewe carries bacteria for life
Sheep gestation period?
- 152 days
When does the majority of foetal growth occur?
- final 60 days
- from day 100-150 growth of placenta has finished
Why were there no gross lesions present in the brain of the sheep at autopsy?
- rare
- when lesions do occur - in caudal brainstem
What is the difference between gross pathology and histopathology?
- histopathology:
- microscopic examination of various forms of tissue
- examination of a biopsy or surgical specimen by a pathologist, after the specimen has been processed and histological sections have been placed onto glass slides
- Gross pathology
- macroscopic manifestations of disease in organs, tissues and body cavities
How do you age a lamb foetus?
- crown-anus length (50-100 days)
- brain weight, long bone length and number of appendicular ossification centres
What biosecurity measures can be taken to reduce Listeria spread between sheep?
- do not feed silage, if you do make sure it is high quality, not rotten, and without soil contamination or prolonged air exposure
- remove left over silage after feeding
- any sick animals isolated
- affected sheep treated with antimicrobials
- recumbent animals - euthanised
What biosecurity measures can be taken to reduce the risk of transmission of Listeria to humans?
- movement of livestock bedding waste from pens to secondary store, and storage under conditions conducive for increased temp
- dont use untreated manure on crops
- wash raw veg, thoroughly cooking meat, hygiene, consume only pasteurized products
- gloves
What is encephalitis?
- inflammation of brain
Which animals is Listeria ivanovii specific to?
- ruminants
What is autolysis?
- the destruction of cells and tissues by their own enzymes
What % of CO2 enhances Listeria growth?
- 10%
What are the clinical signs of Listeria in cattle?
- mainly listeria monocytogenes
- septicaemia- visceral listeriosis
- neural listeriosis - circling disease
- abortion
- iritis
- not eating
- drooping etc
- much more pronounced facial paralysis and go off their food a lot more than sheep
- third eyelid prolapse
- drooping tongue
What is this?
- multifocal bacterial encephalitis
- perivascular cuffing
- inflam cells around vessels in brain
- may see microabcesses
- to confirm 100% Listeria either:
- immunohistochemistry with Listeria antibody
- insitu PCR
What is this?
- Perivascular cuffing
What are these?
- Listeria monocytogenes
- not always in huge numbers
What can be seen here? when would this be seen?
- granulomatous encephalitis- sheep
- seen in chronic cases
What samples would you collect for diagnosis in sheep?
- visceral form - liver, kidney, spleen
- abortion - placenta, foetal abomasal contents, uterine discharge and afterbirth
On farm risk factors for Listeria?
- biosecurity
- rodents
- previous infections on farm
- poor silage making/ storage facilities
How to prevent silage conducting Listeria?
- discard spoiled silage
- clean feed troughs daily
- avoid soil/ manure contamination of feed troughs from tractor wheels
- discard refusals
- clean water troughs regularly
- repaire punctured wrapped bales
- inside of silage bale warm - take it out, cold shock, kick starts the listeria
- use additives
- silage clamps rolled continously
- silage clamps must be sheeted to prevent entry of air
- use block cutter
- cut across a narrow silage face
Listeria Vaccines?
- none licensed in UK
- only autogenous vaccines
- experimental live attenuated vaccine (concern about zoonoses)
If Listeria is inhaled, what does it cause?
- abortion
- latent infection
- septicaemia
Listeria that is ingested and gains entry to tissue:
- localise in intestinal wall, medulla oblongata and placents
- causes encephalitis via minute wounds in bucal mucosa
Which animals does Listeric encephalitis affect?
- sheep
- cattle
- goats
- pigs
- (adult ruminants)
What animals does Septicaemic listeriosis affect?
- dogs
- cat
- pigs
- rabbits
- young ruminants- rumen not functional yet
- (neonatal ruminants, monogastric animals, poultry)
What causes the miliary yellow-white foci in the foetal liver?
- due to necrosis, pus filled, containing listeria bacterium
- liver susceptible- blood supply
What doesnt silage supply?
- calcium
- protein
What type of silage has increased chance of spreading listeriosis?
- maize silage
What BCS should ewes be at lambing?
- 3-3.5
What is the minimum % protein that should be fed?
- 18%
Does Listeria have flagella?
- has Pentrichous flagella at room temp
How long after infection does encephalitis occur?
- 10 days - 3 weeks
How do L.monocytogenes travel in blood?
- via monocytes, macrophages and granulocytes
What is a Gitter cell?
- microglia that transforms into macrophages
What are glial nodules?
- aggregates of reactive astrocytes
What is Torticollis?
- head tilts to 1 side
What happens to the uterus of infected animals?
- normally becomes infected at all stages of pregnancy causing:
- placentitis
- metritis
- still births
- abortions
- potential carrier via vertical transmission
What localised infections occur from Listeria in cows and sheep?
- cattle - chronic/ acute mastitis
- sheep - opthalmitis
