LISTERIOSIS IN RUMINANTS: CLINICAL SIGNS AND PREVENTIVE MEASURES

Listeriosis is a serious infectious disease caused by Listeria bacteria and occurs in many animal species and birds, with ruminants being the most commonly affected. The disease is typically characterized by septicemia, encephalitis, abortion, or stillbirth, leading to significant losses in livestock productivity and health. Notably, listeriosis is closely associated with poor-quality silage that is contaminated or improperly fermented.
In this article, Fivevet provides information to help farmers detect the disease early, manage feed quality-especially silage-and apply appropriate preventive and therapeutic measures to reduce risks, protect animal health, and maintain productivity in ruminant herds. 1. Etiology of Listeriosis
a. Morphology and Structure
Listeria are Gram-positive rods measuring approximately 0.4–0.5 × 0.5–2 µm. They do not form spores and lack a capsule. In young cultures or when freshly isolated from clinical samples, Listeria may appear in a coccoid form.
The genus Listeria consists of seven species, classified into two groups:
- Non-pathogenic group: Listeria murrayi (L. murrayi); Listeria grayi. These species are non-hemolytic, rarely isolated in practice, and are considered non-pathogenic.
- Potentially pathogenic group: Listeria monocytogenes; Listeria ivanovii. Both species are hemolytic and pathogenic. Among them, Listeria monocytogenes is particularly important because it can infect both humans and animals. These species are closely related to L. seeligeri, L. innocua, and L. welshimeri.
+ L. innocua and L. welshimeri: non-pathogenic.
+ L. seeligeri: hemolytic but generally non-pathogenic.
Based on somatic (O) antigens and flagellar (H) antigens, Listeria are divided into 16 serovars. However, these serovars are not host-specific and may occur in different animal species.
b. Resistance
Listeria can survive within a pH range of 5.6–9.6, enabling the bacteria to persist in a variety of environments.
They also show considerable resistance to several chemicals and salts, including:
- Potassium tellurite 0.04%
- Thallium acetate 0.025%
- Potassium thiocyanate 3.75%
- Sodium chloride (NaCl) 10%
- Bile salts 40%
Compared with non-spore-forming bacteria, Listeria demonstrate relatively high heat resistance and can survive under harsh temperature conditions. However, pasteurization processes are still effective in destroying the pathogen.
2. Epidemiology
a. Susceptible species Listeria is widely distributed in the environment, including: Soil and water, silage and fermented livestock feed, organic waste, feces of animals such as cattle, buffaloes, pigs, horses, dogs, cats, birds, and humans.
Abortion cases often occur during the coldest months of the year (winter and early spring).
The encephalitic form typically occurs during cold weather or heavy rainfall, particularly under stressful management conditions such as dietary changes, poor housing, or damp environments.
b. Routes of transmission
Field investigations show that Listeria mainly enters the animal body through the digestive tract. In some cases, infection may occur via the respiratory tract or septicemia.
The most common source of infection is plant material. In soil, plants, and silage, the bacteria can survive for long periods—even for several years—due to their ability to tolerate adverse environmental conditions. Listeria may also be present in: Fecal slurry, respiratory and genital secretions, aborted fetuses and placental tissues of infected animals.
Direct transmission between animals has not been clearly established.
Silage is considered a major source of infection in sheep and cattle. In humans, foodborne outbreaks are often associated with cheese, coleslaw, liver pâté, milk, and poultry meat.
3. Clinical Signs of Listeriosis
The incubation period ranges from a few days to three weeks. The disease commonly manifests in three clinical forms: Septicemic, Miscarriage, Encephalitic.
a. Septicemic form
Affected animals show: High fever, depression, anorexia. This form mainly occurs in young animals, especially especially young ruminants such as calves and lambs, often leading to death. The chinchilla, native to South America, is highly susceptible to this form.
b. Miscarriage and neonatal mortality
This form mainly occurs in ruminants, accounting for approximately 10% of cases. Typical features include:
- Abortion in cattle usually occurs around the 7th month of gestation
- In sheep, abortion occurs around 12 weeks of pregnancy
- Newborn animals are weak and often die within a few hours after birth
- The dam may develop metritis and retained placenta, which can lead to septicemia
c. Encephalitic form (Circling disease)
This is the most common form in ruminants, usually presenting as a subacute or chronic disease.
Affected cattle or buffaloes show: Fever, lethargy, loss of appetite, depression and isolation from the herd. Typical neurological signs gradually develop: Head drooping, facial paralysis, circling movement with progressively smaller radius, lacrimation and nasal discharge, sudden recumbency and inability to stand.
Animals may eventually die, sometimes following respiratory distress and respiratory failure.
In sheep and goats, the disease is usually acute and rapidly fatal.
The disease course may last: 1–7 days in sheep; up to 2 weeks in cattle.
Listeriosis generally occurs as individual cases, and mixed clinical forms are rare.
In humans, the disease most commonly appears as encephalitis, but may also cause endocarditis, dermatitis, and dacryoadenitis, with symptoms including: High fever, headache, meningitis, convulsions, diarrhea. 4. Pathological Lesions
In the encephalitic form, the cerebrospinal fluid appears turbid and the meninges are congested. In some examined areas, the softening of brain tissue is found to be softened.
5. Diagnosis of Listeriosis
Clinical diagnosis is difficult and must be confirmed by isolation of Listeria.
Samples depend on the clinical form:
- Septicemic form: liver, kidney, or spleen.
- Neurological form: cerebrospinal fluid, brain, softening of brain tissue.
- Miscarriage form: placenta, fetal abdominal contents, or urine.
Diagnosis can be confirmed by bacterial culture or PCR detection of Listeria monocytogenes.
6. Prevention of Listeriosis
Due to the epidemiological characteristics of the disease, prevention is challenging. Animals that recover from infection may develop immunity. The most effective preventive measures include: Limiting or avoiding the use of contaminated silage, ensuring proper silage fermentation techniques, reducing stress factors in livestock, especially during winter–spring and rainy seasons, maintaining good housing hygiene and environmental conditions, vaccinating livestock against other diseases (Pasteurellosis, Foot-and-Mouth Disease, Lumpy Skin Disease) to enhance overall immunity.
Immune-support products may also be used to improve resistance in cattle: Five-Mix (Cattle fattening), Five-Prozyme 5way, Five-Caphos, Beta-Glucan.C ,... Currently, no commercial vaccine is available for prevention of Listeria monocytogenes infection.
7. Treatment of Listeriosis
- Recommended management measures include: Isolating affected animals, providing proper care and nutrition, avoiding poor-quality silage, removing leftover feed daily.
- Clean and maintain good hygiene in animal housing and grazing areas, and carry out periodic disinfection using one of the following disinfectants: Five-Iodine, Five-BGF, Five-B.K.G, Five-Perkon 3S,… - For treatment, use one of the following antibiotics: Five-Cfor (5%), Five-Cetifor inj (10%), Five-PenStrep.LA, Five-Azicin, … Supportive treatment may be administered using the following products: Five-Gluco.KC namic, Five-Butasal, Five-Fe.B₁₂, Five-ADE Inj, Five-Acemin.B12, … The dosage and treatment regimen should be applied according to the product label instructions or as directed by a veterinarian. Frequently Asked Questions
1. What is Listeria?
Listeria is a Gram-positive, non-spore-forming rod bacterium capable of causing disease in many animal species, particularly cattle, sheep, goats, and humans. The bacteria are commonly found in soil, water, silage, and animal feces.
2. How is Listeria transmitted to livestock?
Transmission occurs mainly through:
- Ingestion of contaminated feed, especially poorly fermented silage.
- Occasionally through respiratory infection or septicemia.
3. What are the clinical signs of Listeriosis in livestock?
- Septicemic form: high fever, depression, anorexia; common in young animals.
- Miscarriage form: abortions in cattle and sheep; weak or dead neonates.
- Encephalitic form (circling disease): fever, anorexia, facial paralysis, circling, recumbency, and death.
4. Can Listeria infect humans?
- Yes. In humans, the disease most commonly manifests as encephalitis but may also cause endocarditis, dermatitis, and inflammation of the lacrimal glands.
- Common sources include contaminated foods such as: Soft cheese, coleslaw, liver pate, unpasteurized milk, poultry meat.
5. How can Listeriosis be prevented effectively?
- Avoid feeding contaminated or poorly fermented silage.
- Reduce stress in livestock through proper management, maintain clean and dry housing conditions.
- Vaccinate animals against other diseases to strengthen immunity.
- Use immune-enhancing supplements when necessary: Five-Mix, Five-Prozyme 5 way, Beta-Glucan.C,…