Listeriosis in Ruminants: A Comprehensive Guide to Circling Disease

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1. Introduction

Listeriosis, also known as "Circling Disease" or "Silage Sickness," is a sporadic but highly fatal infectious disease in sheep, goats, and cattle. Listeriosis, caused by the bacterium Listeria monocytogenes, results in encephalitis, localized paralysis, and sometimes abortion or septicemia. For the livestock farmer and the veterinarian, the connection between poor quality feed and the neurological disorder is the key to the survival of the herd.

Listeriosis in sheep


​2. The Pathogenesis: From Silage to the Brain

Listeria monocytogenes, the infectious agent, is a ubiquitous microbe. This means the microbe is ubiquitous or "everywhere" in the environment. However, the source of the infectious agent in Listeriosis comes from spoiled silage.

​pH Levels

If the pH levels in the spoiled silage are above 5.0, Listeria will grow and multiply.

​Entry Point

The infectious agent will enter the animal via a wound in the oral mucosa (gums) caused by the animal eating coarse feed or by the eruption of the teeth.

​Neural Migration

The infectious agent will migrate to the brain via the Trigeminal Nerve (5th Cranial Nerve).

​3. Clinical Signs and Symptoms

Listeriosis has long been known for its "asymmetrical" signs and symptoms. This means the infectious disease will affect only one side of the animal's body.

​Unilateral Facial Paralysis

This symptom will be the most common. You will notice the animal's ear will be drooping, the eye will be drooping, and the lip will be hanging on one side.

​Circling Behavior

The animal will circle in a tight circle to the affected side.

​Head Pressing

The animal will stand and press its head against a fence or a wall.

​Excessive Salivation

The animal will salivate profusely because the throat muscles will be paralyzed (Dysphagia).

​Leaning

The animal will lean against a fence to stay up.

4. Differential Diagnosis (Field Guide)

​As a DVM, you must distinguish Listeriosis from other brain-related issues.


Feature Listeriosis CCN (Polio) Pregnancy Toxemia
Primary Cause Bacterial (L. monocytogenes) Thiamine (Vit B1) Deficiency Negative Energy Balance
Body Temperature High Fever (104-106°F) Normal Normal / Sub-normal
Clinical Signs Facial Paralysis & Circling Star-gazing & Blindness Weakness & Ketone Breath
Main Treatment High-dose Penicillin Thiamine Injections Oral Propylene Glycol

5. Post-Mortem Findings

 ​In the necropsy, gross lesions in the brain are normally slight. Nevertheless, a professional vet will observe the following:

>Congestion of the meninges. ​

>Presence of micro-abscesses in the brain stem, which can be seen under a microscope. ​

>Cloudy cerebrospinal fluid (CSF). ​

6. Treatment Protocols 

​Early intervention is the only way to save the animal. Once the animal is "down," i.e., recumbent, the prognosis is extremely poor. ​

High-Dose Antibiotics: 

Listeria is an intracellular pathogen. High doses of Penicillin or Oxytetracycline are required for 3 to 5 days. ​

Anti-inflammatory Drugs: 

Flunixin Meglumine or Dexamethasone helps reduce brain swelling and inflammation. ​

Supportive Care: 

IV fluids (Isotonic Saline or Dextrose) are required if the animal cannot swallow.

 ​7. Prevention and Management 

​Silage Management: 

Avoid feeding the top layer of silage (where oxygen has allowed mold to grow). Also, maintain silage pH at or below 4.5.

Hygiene: 

Keep feeders clean. Discard leftover, fermented feed that has become wet. ​

Zoonotic Risk: 

WARNING! Listeriosis can infect humans. Veterinarians must wear gloves when handling aborted fetuses, and farmers must avoid consuming unpasteurized (raw) milk from infected herds.

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