Listeriosis (Silage disease or Circling disease)

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Listeriosis (Silage disease or Circling disease)

Listeriosis is also known as Silage disease or Circling disease. It is a primarily disease of ruminants, particularly seen in sheep with characteristic septicemia, encephalitis, spinal myelitis, abortion, uveitis, gastroenteritis and mastitis.

Occasionally septicemic form affects horses and pigs.

Etiology

Currently, six species have been identified in the genus Listeria. Of them L. monocytogenes, serotype-5 is pathogenic and L. ivanovii is mildly pathogenic.

Based on somatic (O) and flagellar (H) antigens L. monocytogenes is divided into 16 serovars. Many serovars have been isolated from animals.

  • Virulent strains multiply in macrophages and monocytes and produce haemolysin and listeriolysin O toxins.
  • Listeria spp. can grow and reproduce at temperature from 4ºC to 45°C.
  • At low pH and low temperature reduces the growth rate of the organism.
  • Grow at pH ranges from 4.5-9.6.
  • The organism is resistant to -20°C for 2 years even repeated freezing and thawing unable to destroy the organism.
  • L. monocytogenes able to survive and grow in a wide variety of environments and has a wide range of strain variations.

Epidemiology

Prevalence of infection

Disease is more common in temperate countries as compared to tropical and subtropical countries.

It is a very important disease in North America, Europe, UK, New Zealand and Australia.

Predisposing factors

Reduced host animal’s resistance. Poor nutrition, sudden changes of weather such as very cold and wet weather. Stress due to late pregnancy, parturition and transport. Long periods of flooding and silage feeding.

Transmission

  • The highest prevalence of the disease due to feeding of silage have been recorded.
  • Ingestion of contaminated food, water, milk, silage feeds etc develops listeriosis.

Host affected

  • It is primarily a disease of ruminants, particularly seen in sheep and occasionally in horses and pigs.
  • Introduction of virulent strains through migratory carrier animals, birds, sea gulls is possible.
  • Organism persist for more than 3 months in sheep faeces and survive in soil for 1-2years.
  • The organism has been isolated from 42 species of mammals and 22 species of birds, fish, crustaceans and insects.

Pathogenesis

Listeria is a facultative intracellular organism, infect intestinal cells by direct endocytosis.

The organism is taken up by macrophages and monocytes but the phagocytic activity is prevented by bacterial superoxide dismutase.

Listeriolysin which disrupts lysosomal membranes and permit organism to grow in cytoplasm. Upon ingestion, organism reaches the intestine by penetration and develops, in-apparent/sub-clinical bacteremia which may be cleared by development of immunity.

Bacteremia is frequently sub-clinical and may be accompanied with excretion in milk.

Septicemic listeriosis develops with or without meningitis, most commonly in neonatal ruminants and in adult sheep and goats.

In pregnant animals, invasion into placenta and foetus occurs in 24 hours of onset of infection.

Edema and necrosis of placenta leads to abortion. Infection in late pregnancy results in still birth or birth of young ones that quickly develop a fatal septicaemia. 

  • Thick leathery placenta – Listeriosis – Abortions Encephalitis.
  • Acute inflammation of brain stem is unilateral.
  • Portal of entry is by ascending infection of the trigeminal or cranial nerve following loss of the integrity of buccal mucosa resulting from trauma, shedding of teeth or from periodontitis.
  • Asymmetric cranial nerve function, trigeminal, facial, vestibular, glosso-pharyngeal nerve leads to ipsilateral facial hypalgesia and paralysis.
  • Involvement of vestibular nucleus leads to ataxia, circling and head tilting to the affected side.
  • Dullness, head pressing, delirium spread along optic nerve leads to endophthalmitis in sheep and cattle.
  • Encephalitis is the most prevalent manifestation in sheep and septicaemia in lamb in association with abortion.
  • Mastitis: L. monocytogenes rarely cause mastitis in cattle. It is not invasive or perpetuating organism for the udder.
  • L.ivanovii occasionally causing abortion and encephalitis in ruminants.
  • Suppurative bronchopneumonia and lack of multifocal hepatocellular necrosis are common in aborted foetus.
  • Case fatality rate is 25%.
  • In milk, L.monogytogenes present less than 1 per ml in raw milk and from bacteremic sub clinical animals with mastitis are higher 2000- 5000 per ml.

Clinical Signs

Sheep and Goats

  • In early infection, affected sheep separate from flocks, show high temperature 40ºC, cranial nerve dysfunction, run and fall in a flaccid motion.
  • More acute death in 2-4 days of infection.
  • Affected animals develops in-coordination, head deviation, head tilting, wallowing in circles, unilateral facial hypalgisia,  paralysis  of lips and face.
  • Keratitis, corneal ulceration, strabismus, nystagmus, panopthalmitis with pus evident in anterior chamber of one or both eyes.
  • Paresis of muscles of the jaw, dropped jaw which ensues difficulty in prehension and mastication.
  • Poll-nose relationship, recumbent, death due to respiratory failure. In young ones onset is sudden and the course of the disease is short.
  • Death occurs in 2-3 days.
  • Abortion occurs in 3 months of pregnancy.
  • Abortion is as high as 15% with annual recurrence.
  • Retained placental membrane, mortality in ewes in case of foetus retention.
  • Abortion due to L. ivanovii is sporadic in cattle.
  • In sheep and goats causes outbreak, still birth and birth of live infected lambs.

Enteritis Weaner sheep: Initially found dead. Lethargy, anorexia, pass loose green coloured faeces. Pregnant ewes may abort.

Cattle

  • Course of the disease in adult cattle is 1-2 weeks and in calves disease is more acute and death follows in 2-4 days.
  • Fever 40.5ºC, abortion, still birth (sporadic) usually occurs in last trimester of pregnancy, retained placental membrane, Abortion seen after silage feeding.
  • Encephalitis  signs include circling, ptosis, half chewed food in the mouth and unilateral facial paralysis.
  • Septicemic listeriosis Acute septicaemia: L. monocytogenes is not common in adult ruminants.
  • No nervous signs but depression, weakness, emaciation, pyrexia, diarrhoea, hepatic necrosis and  gastroenteritis.
  • Corneal opacity, dyspnoea, nystagamus and mild opisthotonus is noticed.
  • Death occurs in 12 hours following infection.
  • At necropsy, opthalmitis, serofibrinous meningitis observed. Septicaemia is also recorded in foals.
  • Inflammation of single quarter or both quarter.
  • Chronic mastitis show poor response to treatment, high somatic cell count in milk but milk appears normal.
  • Septic myelitis Fever, ataxia, initial knuckling of hind limbs, weakness, and paralysis.
  • No cranial nerve involved.
  • Animals affected appear to be alert, bright and eat well.

Opthalmitis Iritis: Swelling of iris, constriction of pupil. Advanced cases, pannus and corneal opacity may be uni/bilateral

Necropsy Findings

  • Encephalitis: Visual lesions occurs as multiple foci of necrosis in the liver, spleen, myocardium and in septicaemic form.
  • Enteritis, Ulcerative abomasitis, typhlo-colitis, micro-abcessess through out the intestine, infiltration with neutrophils in mucosa or lamina muscularis of the abomasum.

Diagnosis

  • Based on clinical signs and necropsy findings.
  • Isolation of organism by culture.
  • Cerebrospinal fluid shows the increased protein and leucocytes content.
  • Most of which are mononuclear cells or lymphocytes.
  • Agglutination and Complement Fixation Tests can be performed to detect antibody.
  • Molecular diagnosis by PCR.
  • Micro-abscess present in CNS is important.
  • Cold enrichment techniques is essential.
  • Gram staining of paraffin embedded tissue may permit confirmation
  • Fluorescent antibody technique and immuno peroxidase test is essential.

Sample Collection

  • Vaginal secretions
  • Aborted part
  • milk
  • Faeces
  • Tonsils
  • Cerebrospinal fluid
  • Mid sagittary section of brain, brain stem (chilled or frozen) and formalin fixed spinal cord segment.

Differential Diagnosis

Treatment

  • Chlortetracycline: 10 mg/kg body weight per day for 5 days for meningo-encephalitis for cattle
  • Inj. Penicillin-44000 IU/kg body weight, I/M daily for 7 days or 10-14 days.
  • Supportive therapy using parenteral fluids, neurotropic vitamins and minerals.

Prevention

Live attenuated vaccine shown to induce protection. Commercial killed vaccine also available.

Control

  • Cell mediated immunity is important.
  • Proper care in silage preparation.
  • Avoid soil contamination and mole hills.
  • Avoid eye contact with silage.
  • The organism is susceptible to various common disinfectants.
Listeriosis (Silage disease or Circling disease) in a Sheep

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