Transmission and Epidemiology of Caseous Lymphadenitis in Sheep and Goats

Caseous lymphadenitis (CLA) is a contagious disease that can become firmly established within a flock if transmission pathways are not recognised early. Once infected animals are introduced, the prevalence of the disease can increase considerably over the following years, making prevention and early intervention essential. Understanding how Corynebacterium pseudotuberculosis spreads and the factors that influence its persistence allows veterinarians to develop practical flock health strategies aimed at reducing disease transmission and limiting long-term economic losses^1,2,3. 

Introduction of Infected Animals Drives Disease Spread 

The primary source of infection is the introduction of infected or abscessed animals into a susceptible flock. These animals act as reservoirs of C. pseudotuberculosis, allowing the organism to spread gradually to healthy flock mates. Once established, disease prevalence may increase dramatically within two to three years if infected animals are not identified and managed appropriately^1,2,3. 

This highlights the importance of considering flock history and animal movement whenever CLA is suspected. 

Environmental and Management Factors Influence Transmission 

Transmission is closely linked to management practices that create opportunities for skin injury and environmental contamination. Measures that reduce wounding can significantly lower the risk of bacterial entry. 

Recommended practices include using smooth wire fencing, sterilising surgical instruments and shearing equipment, using disposable needles, implementing insect control, and disinfecting wounds with 10% iodine. Housing facilities should also be sanitised using 10% formaldehyde to minimise environmental contamination⁴. 

Additional flock management practices can further reduce transmission. Isolating young sheep after shearing, shearing younger animals before older flock members, minimising post-shearing cover time, and reducing ectoparasite dipping are all recommended to decrease exposure to the organism². 

Disease Distribution Around the World 

CLA occurs throughout the world's major sheep-producing regions and remains one of the most important chronic diseases affecting small ruminants. High prevalence has been reported in Australia, Canada, the United States, Mexico, Argentina, Brazil, and several African countries, where reported prevalence ranges from 12.60% to 61.00%^4,5. 

Lower prevalence has been reported in several European countries, including the Netherlands, Denmark, Norway, England, Italy, Germany, Iceland, Slovakia, the Czech Republic, Poland, and Spain, although Spain has recorded comparatively higher rates within Europe^4,5. 

In Croatia, available data remain limited. Clinical and bacteriological investigations reported infected goat flock prevalences of 12.5% and 30% in two separate investigations^6,7. 

Why Disease Prevalence Varies 

Differences in reported prevalence between regions are influenced by several interacting factors. Management systems, climatic conditions, and the survival of C. pseudotuberculosis in contaminated environments all contribute to disease occurrence. Ambient temperature affects bacterial viability, while the endemic nature of CLA also influences herd immunity and animal susceptibility⁴. 

Awareness and diagnostic practices further affect reported prevalence. In one survey involving 264 veterinarians and 510 sheep farmers in the United Kingdom, only 18% of veterinarians had encountered at least one case of CLA, whereas 45% of farmers reported observing abscesses in their sheep. Laboratory investigation of 32 farms subsequently confirmed CLA on 24 farms, illustrating that disease occurrence may be underestimated when abscesses are not investigated further⁸. 

Practical Clinical Insights 

Successful control of CLA begins with understanding how the disease enters and persists within a flock. Careful assessment of animal introductions, routine surveillance for abscesses, attention to management practices that minimise skin injuries, and prompt investigation of suspicious lesions can substantially reduce transmission. Recognising that disease prevalence is influenced by management, environmental conditions, and awareness also helps guide practical flock health planning and long-term disease control. 

References 

1. Guimarães AS, Seyffert N, Bastos BL, Portela RW, Meyer R, Carmo FB, Cruz JC, McCulloch JA, Lage AP, Heinemann MB, Miyoshi A. Caseous lymphadenitis in sheep flocks of the state of Minas Gerais, Brazil: prevalence and management surveys. Small Ruminant Research. 2009 Nov 1;87(1-3):86-91. https://www.sciencedirect.com/science/article/pii/S0921448809001850 

2. Windsor PA. Control of caseous lymphadenitis. Veterinary Clinics: Food Animal Practice. 2011 Mar 1;27(1):193-202. https://www.academia.edu/download/45713101/j.cvfa.2010.10.01920160517-6272-r4hlkj.pdf 

3. Baazizi R, Mimoune N, Chahed A, Baroudi D, Ramoul K, Abdul-Hussain AS, Ait Issad N, Khelef D. Prevalencija i identifikacija Corynebacterium pseudotuberculosis u zaklanih ovaca u središnjoj regiji Alžira. Veterinarska stanica. 2024;55(3):289-99. https://hrcak.srce.hr/file/439278 

4. Dopuđ M, Reil I, Zdelar-Tuk M, Špičić S, Duvnjak S. Caseous Lymphadenitis in sheep and goats–“Cheese Glands”. Veterinarska stanica. 2025;56(3):303-16. https://hrcak.srce.hr/file/462890 

5. Ruiz H, Ferrer LM, Ramos JJ, Baselga C, Alzuguren O, Tejedor MT, de Miguel R, Lacasta D. The relevance of caseous lymphadenitis as a cause of culling in adult sheep. Animals. 2020 Oct 24;10(11):1962. https://www.mdpi.com/2076-2615/10/11/1962 

6. Habuš J, Matanović K, Majetić ZŠ, Rukavina T, Ćorić A, Milas Z, Starešina V, Martinec BŠ, Turk N. Comparison of the epizootiological and clinical features of caseous lymphadenitis and Morel's disease in goats. https://www.researchgate.net/profile/Josipa-Habus/publication/275961288 

7. Bacan I, Habuš J, Štritof Z. Utvrđivanje prisutnosti i proširenosti kazeoznog limfadenitisa u stadima ovaca i koza. Veterinar. 2022 Sep 20;60(1.):41-9. https://hrcak.srce.hr/file/412356 

8. Domínguez MR, Jimenez RM, Guerreo JA. Caseous lymphadenitis: Virulence factors, pathogenesis and vaccines. Review. Rev. Mex. Cienc. Pecu. 2021;12:1221-49. https://classic.scielo.org.mx/pdf/rmcp/v12n4/2448-6698-rmcp-12-04-1221-en.pdf