Difference between revisions of "Listeria species"

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

Latest revision as of 10:27, 14 May 2010