Todayโs path rounds are on ๐๐๐ฌ๐๐จ๐ฎ๐ฌ ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐๐๐๐ง๐ข๐ญ๐ข๐ฌ!
๐๐ก๐๐ญ ๐ข๐ฌ ๐ข๐ญ?
๐๐๐ฌ๐๐จ๐ฎ๐ฌ ๐ฅ๐ฒ๐ฆ๐ฉ๐ก๐๐๐๐ง๐ข๐ญ๐ข๐ฌ is an extremely common disease, caused by a bacterial infection. In this disease, the lymph nodes become infected (lymphadenitis) and turn cheesy (caseous). Yum 
๐๐ก๐จ ๐ ๐๐ญ๐ฌ ๐ข๐ญ?
This disease is most commonly seen in sheep and goats, however other species, including humans, can also be affected.
๐๐ก๐๐ญ ๐๐๐ฎ๐ฌ๐๐ฌ ๐ข๐ญ?
Caseous lymphadenitis is caused by ๐๐จ๐ซ๐ฒ๐ง๐๐๐๐๐ญ๐๐ซ๐ข๐ฎ๐ฆ ๐ฉ๐ฌ๐๐ฎ๐๐จ๐ญ๐ฎ๐๐๐ซ๐๐ฎ๐ฅ๐จ๐ฌ๐ข๐ฌ. This bacteria often enters the sheep or goat through a skin wound, which allows it to access nearby lymph nodes. Once in the lymph node, the bacteria causes ๐๐๐ฌ๐๐๐ฌ๐ฌ๐๐ฌ (accumulations of dead white blood cells and bacteria) to form. To try and control the abscess, the body produces a ๐๐๐ฉ๐ฌ๐ฎ๐ฅ๐ out of fibrous tissue, to prevent the bacteria from spreading. However, encapsulating the abscess doesnโt prevent more pus from accumulating! As the abscess continues to grow, the capsule ruptures, and a new capsule is formed. Over time, this produces a characteristic pattern called ๐๐จ๐ง๐๐๐ง๐ญ๐ซ๐ข๐ ๐ฅ๐๐ฆ๐๐ฅ๐ฅ๐๐ญ๐ข๐จ๐ง๐ฌ, which look like tree rings. Neat!
๐๐ก๐ฒ ๐ข๐ฌ ๐ญ๐ก๐ข๐ฌ ๐ ๐ฉ๐ซ๐จ๐๐ฅ๐๐ฆ?
Caseous lymphadenitis usually isnโt fatal, however it does leave the animal with very large, swollen and ugly looking lymph nodes. These animals often will be condemned at slaughter, reducing the income for the farmer. In some cases, the bacteria may spread to lymph nodes in the lungs, hindering breathing, or to the mammary gland, causing mastitis (infection of the mammary gland) and reduced milk production.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐๐ข๐๐ ๐ง๐จ๐ฌ๐๐?
Often, the appearance of multiple enlarged lymph nodes on a sheep or goat is sufficient to make the diagnosis. If needed, a sample from the lymph node can be sent for bacterial culture, to confirm the diagnosis.
๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐? ๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ฉ๐ซ๐๐ฏ๐๐ง๐ญ๐๐?
Unfortunately, the capsule around the abscesses makes caseous lymphadenitis difficult to treat, as antibiotics often cannot penetrate into the capsule. It is also very common for animals to have internal lymph nodes affected, meaning that direct injection of antibiotics into the accessible, external lymph nodes or other external treatments does not actually resolve the issue. For this reason, caseous lymphadenitis is considered โincurableโ, and often these animals are culled.
Prevention usually involves quarantining affected animals, testing any animals introduced to the farm for the bacteria, and preventing external wounds to the animal through safe fencing and proper wool shearing protocols. There are also vaccines available to prevent the disease, however they are not 100% effective.
๐๐ก๐จ๐ญ๐จ๐ฌ
1) A sheep with a swollen lymph node under its jaw.
2-6) Examples of the lamellations characteristic of this disease! So satisfying 
๐๐จ๐ฎ๐ซ๐๐๐ฌ
Maxie, G. Jubb, Kennedy and Palmerโs Pathology of Domestic Animals, Volume 3. Sixth Edition.
Washburn K. Caseous lymphadenitis of sheep and goats. Merck Veterinary Manual 2020.
Photos 1-6 ยฉ Noahโs Arkive contributors Leathers, King, Reece licensed under CC BY-SA 4.0.
