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MCI Santé Animale

Caseous Lymphadenitis

Introduction

Caseous Lymphadenitis (CLA), commonly referred to as Abscess Disease, is a chronic, contagious, and infectious disease of small ruminants primarily caused by Corynebacterium pseudotuberculosis (Windsor, 2011). The disease is characterized by the formation of abscesses containing thick, caseous pus within superficial and deep lymph nodes, as well as in internal organs such as the lungs, liver, mammary gland, and occasionally the skin (Guimarães et al., 2011).

CLA is a major health and economic concern in sheep and goat production, leading to reduced productivity, carcass condemnations at slaughter, and a decline in the commercial value of affected animals, particularly during periods of high market demand such as Eid al-Adha.

Etiology

Caseous Lymphadenitis is primarily caused by Corynebacterium pseudotuberculosis, a Gram-positive bacterium capable of surviving for extended periods in the environment (Rodríguez Domínguez et al., 2021).

Other pyogenic bacteria may occasionally produce similar lesions, including:

The disease mainly affects adult sheep and goats. Transmission generally occurs through contamination of skin wounds created during shearing, injections, fighting, or other injuries, as well as through direct contact with ruptured abscesses that contaminate the environment (Guimarães et al., 2011).

Clinical Signs and Disease Forms

Abscesses typically range from 0.5 to 15 cm in diameter and are surrounded by a fibrous capsule that may exceed 3 mm in thickness. In sheep, the abscesses often display the characteristic "onion-ring" appearance, containing thick greenish-yellow caseous pus. Over time, the purulent material may become dry and calcified (Dopuđ et al., 2025).

Depending on the location of the lesions, two principal clinical forms are recognized:

Prevention and Treatment

Treatment of abscesses through drainage and cleaning should be performed with great care to prevent environmental contamination and further spread of the disease within the flock (Windsor, 2011).

Antibiotic therapy may be used to control bacterial infection; however, its effectiveness is often limited by the thick fibrous capsule surrounding the abscesses, which hinders antimicrobial penetration (El Damaty et al., 2023).

Vaccination

Vaccination is currently considered the most effective strategy for reducing the prevalence of Caseous Lymphadenitis in sheep and goat flocks (de Pinho et al., 2021).

Vaccines targeting Corynebacterium pseudotuberculosis help reduce the incidence of abscess formation, limit bacterial transmission within the flock, and minimize the economic losses associated with the disease.

MCI Solutions

As part of its commitment to controlling Caseous Lymphadenitis, MCI Santé Animale conducted extensive field investigations on clinically affected animals to identify the principal bacterial agents associated with the disease.

Bacteriological analyses consistently identified the following pathogens:

Based on these field investigations and laboratory findings, MCI Santé Animale developed Pyovac®, a vaccine designed to help protect sheep and goat flocks against the principal bacterial pathogens responsible for Caseous Lymphadenitis and abscess disease.

When combined with twice-yearly vaccination and rigorous biosecurity measures—including isolation of affected animals, proper disinfection of equipment, and careful management of abscesses—Pyovac® contributes significantly to improving disease control and reducing bacterial transmission within small ruminant production systems.