CASE NOTES

Hepatic necrobacillosis in lambs

BR Watt, Central Tablelands Local Land Services and Patrick Staples, Elizabeth Macarthur Agricultural Institute, Menangle

Posted Flock & Herd March 2023

History

In August 2020 a mob of 170-180 White Dorper x Aussie White mature ewes had almost finished lambing over an eight-week period. The ewes received a pre-lambing macrocyclic lactone drench and a 5-in-1 clostridial vaccine. Two lambs had previously been found stillborn. Two lambs were found sick on 11 August 2020. Case 1 died on that day and was necropsied by the owner. Case 2 was dull and sick and was euthanased on 12 August 2020 prior to necropsy.

Clinical findings

Case 2 was a well-grown, approximately three-week-old male White Dorper-type lamb, which was dull and trembling. The rectal temperature was 37 degrees Celsius. The lamb had a heart rate of about 50 bpm and was panting. The liver could be palpated in the right anterior abdomen. The mucous membranes were normal.

Figure 1. Case 2. Moribund three-week-old lamb

NECROPY FINDINGS

Case 1. Necropsied by owner first then by the first author. It had a spectacularly enlarged liver with multiple dull yellow lesions about 5mm in diameter, both on the surface and through the parenchyma of the liver.

Case 2. Also had a spectacularly enlarged liver with multiple dull yellow spherical lesions about 5mm in diameter, both on the surface and through the parenchyma of the liver. It also had similar yellow lumps on the serosa of rumen, abomasum, and diaphragm and adherent to the liver. There was a large irregular haemorrhage in the mucosa of the abomasum. The lamb had yellow pasty gut contents while the lungs and kidneys appeared normal.

Image of lamb post-mortem showing abdominal and thoracic contents

Figure 2. Case 2. Abdominal and thoracic contents

Image of lamb post-mortem showing liver on cut section

Figure 3. Case 2. Liver, cut section

Image of lamb post-mortem showing mucosal haemorrhage

Figure 4. Case 2. Abomasal mucosal haemorrhage

Image of lamb post-mortem showing lesions on liver and rumen

Figure 5. Case 2. Lesions on liver and serosal surface of the rumen

Histopathology

Fixed liver and kidney were submitted from case 1. Fixed liver, kidney, umbilicus, mesenteric lymph nodes, abomasum and small intestine were submitted from case 2.

The livers of both lambs contained multiple focal areas of coagulative necrosis surrounded by margins of viable and degenerate neutrophils, macrophages and haemorrhage. Numerous bacteria were present within the necrotic tissue, mainly at the margins of the lesions.

The umbilicus of case 2 showed peritoneal exudate comprised of small amounts of fibrin and moderate numbers of viable and degenerate neutrophils, with sparse infiltrates of neutrophils in subjacent connective tissue. However, there was no evidence of inflammation of the overlying umbilical skin.

Abomasal sections of case 2 showed only scattered small foci of mucosal congestion and haemorrhage. The mesenteric lymph nodes contained moderate numbers of neutrophils within subcapsular and medullary sinuses.

In summary, the following morphological diagnoses were made:

Liver: Severe, subacute, multifocal, necrotising, suppurative hepatitis with intralesional bacteria
Umbilicus: Moderate, acute, fibrinosuppurative peritonitis
Mesenteric lymph node: Moderate, acute, suppurative lymphadenitis.

BACTERIOLOGY

Aerobic culture obtained a sparse mixed growth from the liver of case 1 and no growth from the liver of case 2.

Anaerobic culture obtained no significant growth from the liver of case 1 and a profuse pure growth of Fusobacterium necrophorum from the liver of case 2.

Discussion

The only significant bacterial isolate was Fusobacterium necrophorum cultured from case 2. The hepatic lesions are morphologically consistent with Fusobacterium infection, being firm rounded areas of caseous necrosis bordered by infiltrates of neutrophils and macrophages. Fusobacterium necrophorum is a common inhabitant of the environment of farm animals and is also present within gastrointestinal microflora. The most common route of hepatic infection in young lambs is extension via umbilical veins from an omphalophlebitis. Haematogenous spread by portal vein emboli from a primary rumenitis has also been documented. Unsanitary environmental conditions may predispose to infections. Bacterial flora within the lesions may be mixed. Bacteria that may be isolated from omphalogenic abscesses include Trueperella pyogenes, Fusobacterium necrophorum, streptococci and staphylococci.

In this case the route of infection is not confirmed. There was no gross evidence of omphalophlebitis nor rumenitis. There was histological evidence of peritonitis at the umbilicus of case 2. This finding supports a primary umbilical infection, however this lamb also had widespread serosal lesions over the rumen, abomasum and diaphragm, so it could have been secondary. Abomasal mucosal haemorrhage was present, however this finding alone does not provide sufficient evidence for a primary abomasal infection site. Primary ruminal lesions usually include obvious ulceration and necrosis, not just haemorrhage.

References

Marsh H (1944). Necrobacillosis of the rumen in young lambs. Journal of the American Veterinary Medical Association 104: pp 23-25
Ramos-Vara JA, Rook J, Scanlan CM, Mugli F and Yamini B (1997). Fusobacterim necrophorum septicaemia in a lamb: pathologic and microbiologic characterization. Journal of Veterinary Diagnostic Investigations 9: pp 79-82
Maxie MG, Ed. (2016). Jubb, Kennedy and Palmer's Pathology of Domestic Animals: 3 Volume Set, Elsevier Inc.