|
|
| (6 intermediate revisions by 5 users not shown) |
| Line 1: |
Line 1: |
| − | <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>
| |
| − | | |
| − | ===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
| |
| − | | |
| − | | |
| − | ===Characteristics===
| |
| − | | |
| − | *Small Gram negative rods
| |
| − | *Catalase positive, oxidase negative
| |
| − | *Tumbling motility
| |
| − | *Facultative anaerobes
| |
| − | *''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
| |
| − | | |
| − | | |
| − | ===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
| |
| − | **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
| |
| − | *Septicaemic listeriosis:
| |
| − | **Incubation perios 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
| |
| − | | |
| − | *''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
| |