Listeriosis

Also known as:

Circling disease Silage sickness

Description

Listeriosis is a bacterial infection caused by Listeria species. It affects a wide range of animals and is an important zoonosis.. L.monocytogenes is found in silage and is the main source of contamination for animals. Soil and the mammalian gastrointestinal tract are natural reservoirs for L.monocytogenes and if ingested by grazing animals the bacteria will further contaminate the pasture. The bacteria is very resistant to drying and can survive at a variety temperatures and PH.

Signalment

Affects a range of animals including sheep, cattle, goats and birds. Most commonly affects adult ruminants that are being fed contaminated silage over the winter.

Diagnosis

Lumbosacral CSF can be collected under local anaesthesia and if the animal is infected will show an increased protein count and mild pleocytosis with large mononuclear cells. Isolation of L. monocytogenes provides a definitive diagnosis of listeriosis. The preferred samples for culture are brain, aborted foetus or placenta. Immunofluorescence can also be used to identify L.monocytogenes on smears taken from dead or aborted animals. Serology is not used as many healthy animals have high Listeria titres.

History and Clinical Signs

In ruminants listeriosis is seen as meningoencephalitis, in monogastric animals and young ruminants it causes a septicaemia. If animals are infected whilst pregnant this can cause abortion. Following abortion the animal normally recovers. Listeriosis can also manifest as conjunctivitis, pneumonia, myocarditis and endocarditis.

Treatment

L monocytogenes is susceptible to a range of antibiotics including penicillin, ceftiofur, erythromycin, and trimethoprim/sulfonamide. In order to achieve high enough levels in the brain high doses are required daily for 1-2 weeks. In an outbreak, affected animals should be isolated, treated and feeding the silage that the affected animal recieved should be discontinued. All bedding should be destroyed and buildings should be thoroughly cleaned. To avoid further outbreaks, ensure animals are fed good quality silage and minimise soil contamination when making silage. For ocular listeriosis Sub-conjuntival antibiotics and corticosteroids can be given.

Prognosis

Recovery depends on rapid diagnosis of the disease. If treated animals can recover however if signs of encepalitis are present treatment is often unsuccessful.

References

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

• Occurs in North and East Europe and North America

Outbreaks of listeriosis often linked to silage feeding

Treatment and control

• Ampicillin or amoxycillin in early stages of septicaemic listeriosis
• Avoid poor quality silage and discontinue silage-feeding in an outbreak

Causes abortions in cattle and sheep last third of pregnancy. Foetal membranes often retained leading to metritis. The placenta is covered by purulent exudate and there are focal pinpoint yellow lesions in foetal liver.

• 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