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| − | <big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
| + | #REDIRECT[[:Category:Listeria species]] |
| − | <big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
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| − | ===Overview===
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| − | *6 species
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| − | *Saprophytes in soil
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| − | *''L. monocytogenes'' and ''L. ivanovii'' are pathogens
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| − | *Carried by sheep and goats and shed in faeces and milk especially during stress
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| − | *Can cause septicaemia, encephalitis, abortion and endophthalmitis in ruminants
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| − | *Outbreaks of listeriosis often linked to silage feeding
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| − | *Occurs in North and East Europe and North America
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| − | ===Characteristics===
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| − | *Small Gram negative rods
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| − | *Catalase positive, oxidase negative
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| − | *Tumbling motility
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| − | *Facultative anaerobes
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| − | *Intracellular pathogens
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| − | *''L. monocytogenes is haemolytic on blood agar due to a cytolytic protein, listeriolysin; grows at range of pH values and temperatures
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| − | *''L. ivanovii produces strong haemolytic zone
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| − | *Small, smooth, transparent colonies after 24 hours incubation
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| − | *Grow on non-enriched media
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| − | ===Pathogenesis and pathogenicity===
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| − | *Infection by ingestion of contaminated feed
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| − | *Bacteria penetrate M cells in intestinal Peyer's patches
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| − | *Spread to tissues via blood and lymph
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| − | *Transplacental transmission in pregnant animals
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| − | *Bacteria may gain entry via breaks in oral or nasal mucosa, migrate in cranial nerves to cause neural signs
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| − | *Causes formation of microabscesses and perivascular lymphocytic cuffs in brainstem
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| − | *''L. monocytogenes'' can replicate within phagocytic and non-phagocytic cell, and pass between cells without being exposed to the immune system
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| − | *Surface proteins known as internalins allow adherence and uptake of the bacteria into cells
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| − | *Listeriolysin produced by virulent strains destroys membranes of phagocytic vacuoles, releasing the bacteria into the cytoplasm
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| − | *Listeria are motile in the cytoplasm
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| − | *Bacteria induce formation of pseudopod projections in the cytoplasmic membrane, which are taken up with the bacteria into adjacent cells
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| − | *Cell-mediated immune response required for protection
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| − | ===Clinical infections===
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| − | *Outbreaks of listeriosis caused by ''L. moncytogenes'' seasonal and linked to silage feeding
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| − | *Replicates in poor quality silage where the pH excedes 5.5
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| − | *Animals highly susceptible during pregnancy due to lowered cell-mediated immunity
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| − | *Neural listeriosis:
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| − | **Incubation period 14-40 days
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| − | **Meningoencephalitis
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| − | **Dullness, circling, head tilt, facial paralysis, drool saliva, droop of eyelid and ear
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| − | **Exposure keratitis
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| − | **Fever during early stages
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| − | **Recumbency and death within a few days in sheep and goats
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| − | **Abortion up to 12 days after infection in cattle; usually recover but may get septicaemia
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| − | *Septicaemic listeriosis:
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| − | **Incubation perios 2-3 days
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| − | **Lambs and occasionally pregnant sheep
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| − | **Occurs in newborn piglets, foals, poultry, adult sheep
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| − | *Keratoconjunctivitis in cattle and sheep - direct contact with silage via eye
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| − | *Pneumonia, myocarditis, enodcarditis
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| − | *Zoonosis - consumption of contaminated unpasteurised milk; memingitis and meningoencephalitis; abortion
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| − | *''L. ivanovii causes sporadic abortion in sheep and cattle
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| − | *''L. innocua'' rarely causes ovine meningoencephalitis
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| − | ===Diagnosis===
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| − | *Specimens should include CSF in neural cases, cotyledons in abortion, liver, spleen and blood in septicaemia
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| − | *Immunofluorescence using monoclonal antibodies
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| − | *Histology of brain demonstrates microabscesses and lymphocytic cuffing in brainstem
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| − | *Smears of cotyledons
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| − | *High protein and cell counts in CSF
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| − | *Isolation on blood and MacConkey agar
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| − | ===Treatment and control===
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| − | *Ampicillin or amoxycillin in early stages of septicaemic listeriosis
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| − | *Sub-conjuntival antibiotics and corticosteroids for ocular listeriosis
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| − | *Avoid poor quality silage and discontinue silage-feeding in an outbreak
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