Listeriosis:

Syn: Circling Disease, Meningo-encephalitis, Silage disease

• It is infectious fatal disease of wide range of animals and man
• It is characterized by encephalitis and also causes abortion, endometritis and repeat breeding in farm animals.

Etiology:

• Listeria monocytogenes
• Gram+ve, rod shaped, diphtheroid bacilli
• It is isolated from faeces and silage.
• It can be destroyed easily by ordinary disinfectants but may survive in soil and silage for considerable period of time.

Epidemiology:

• Disease is worldwide in distribution and reported from various parts of the world.
• 5 serotypes have been identified from farm animals.
• Its higher incidence is during spring and early summer in animals.
• It is zoonotic in nature and have occupational risk.
• Disease has been recorded from cattle, buffalo, sheep, goat, horse, pig, dog, cat, rabbit, birds and fish.
• Feeding poor quality silage (pH > 5.5) favors listeria growth.

Transmission:

• Silage is important spreader of disease.
• Organism may be transmitted through oral mucosa or damaged buccal epithelium.
• Direct contact with contaminated environment; eg; soil, water, feces
• Vertical transmission is rare in animals but may occur.

Pathogenesis:

Organism gains entry through gastrointestinal mucosa, reaches circulation and produced bacteremia. Organism gets localized in various organs. Organism may pass through nasal mucosa and traverse the brain stem through trigeminal nerves. Organism gets lodged in brain stem and produces lesion in pons, midbrain and medulla. Infection in uterus leads to abortion.

Clinical Signs:

Disease is manifested in 3 forms, i.e. encephalitic, septicemic and abortive.

Encephalitic form:

• Affected animals becomes dull and depressed
• High rise of body temperature
• Animals shows a dummy syndrome on progression of disease
• Head pressing against a barrier
• Unilateral facial paralysis with drooling of saliva.
• Panophthalmitis with pus in anterior chamber of one or both eyes may appear.
• Animals shows circling movement either in left or right direction.
• Death occurs due to respiratory failure.

Septicemic form:

• Depression
• Weakness
• Emaciation
• Pyrexia
• Diarrhoea
• Corneal opacity
• Opisthotonus, dyspnea, nystagmus may appear
• Death within 12 hours following onset of disease

Abortive Form:

• Abortion occurs in early pregnancy
• In late pregnancy, still birth occurs
• Retention of placenta after abortion is very common.
• In sheep and goat, abortion takes place usually after 12^th weeks

PM lesions:

• No gross characteristic lesion
• CSF shows cloudiness due to presence of excess globulin and leukocytes.
• Eyes shows signs of panophthalmitis
• Yellow necrotic foci on liver, spleen, endocardium, pericardium and lungs.
• Placenta and uterus show signs of placentitis and endometritis.

Diagnosis:

• Based on history; Feeding of silage
• Clinical findings
• Clinical pathology: There is increased level of circulating monocytes
• Isolation and identification of organism in selective agar media
• Animal inoculation: intracerebral injection of infective material causes death in white mice in 2-3 days.
• ELISA with CFT
• FAT

Differential diagnosis:

1. Rabies:

• History of animal bite
• Bellowing, ascending paralysis
• Salivation, tenesmus

2. Lead poisoning:

• Blindness
• Clonic spasm
• Convulsion
• History of poisoning

3. Nervous form of Ketosis:

• History of parturition
• Sweetish smell from breath
• Ketonuria, ketolactia
• Respond to glucose therapy

Treatment:

• Chlortetracycline @ 10mg/kg, b.wt. for 5-7 days through IM is suggested.
• Penicillin @ 44000 IU/kg, b.wt.. IM for 7 days may be attempted.
• Sulphonamide @100-150 mg/kg, b.wt. daily for 3 days has been used successfully.
• Intravenous oxytetracycline @16.5mg/kg/day is also effective.
• Supportive therapy; fluids and electrolytes is also required for animals having difficulty eating and drinking.
• Administration of high-dose dexamethasone @ 1 mg/kg, IV is proved to be beneficial.

Control:

• Litters and bedding materials should be carefully disposed by burning.
• Rotten vegetation shouldnot be fed.
• Premises should be disinfected thoroughly by appropriate disinfectants such as Virkol, formalin, phenol
• Silage feeding should be restricted in enzootic areas.
• Tetracycline or chlortetracycline should be added in feed as preventive measure when there is outbreak.
• Vaccination; live vaccine; 2-3 ml at age of 3 months SC is done.

Zoonotic Risk:

• All materials from suspected clinical cases of listeriosis carries zoonotic risk and should be handled with caution.
• Aborted fetus and necropsy of the septicemic animals presents the greatest hazard.
• Humans have developed fatal meningitis, sepsis, and popular exanthema of the arms after handling aborted material.
• Pregnant animals and women should be protected from infection because of danger to fetus with possible abortion, stillbirth and infection of neonates.
• monocytogenes is usually confined to brain and presents little risk of transmission, unless brain is handled during necropsy.
• monocytogenes can be isolated from milk of mastitis, aborting and apparently healthy cows.