CASE NOTES
Malignant oedema associated with naval infection in lambs
Bruce Watt, Central Tablelands Local Land Services, Bathurst and Anne Jordan, Elizabeth Macarthur Agricultural Institute, Menangle
Posted Flock & Herd December 2021
Introduction
Neonatal lambs can acquire infections through the umbilicus, by ingestion, in association with existing conditions such as starvation and subsequent to procedures performed at marking. Clostridium septicum is one of the more common isolates but usually post lamb marking (Dennis 1974).
In these two cases, lambs were infected and died before marking. In both cases the owners shedded at least some of the ewes for lambing.
History
CASE 1. In a mob of 200 registered Poll Dorset ewes shedded for lambing, 6 initially vigorous lambs that had walked and nursed, died at 3-5 days. The owner noticed that they had abdominal distension before death.
CASE 2. In a mob of approximately 2000 mixed age Composite ewes lambing in July, the owner noticed at least 10 lambs that stood and nursed but were found dead 2-3 days later.
Necropsy findings
CASE 1. On the 7 May 2021, a well grown male lamb weighing approximately 8 kg was necropsied. The lamb had marked subcutaneous red-stained oedematous fluid from the inguinal area to the ventral thorax with numerous small to coalescing gas bubbles (Image 2). The ventral body wall was thickened, blood stained and emphysematous and the navel was moist and dark brown.
CASE 2. On 15 July 2021 a representative lamb was necropsied. The owner observed that the lamb, weighing approximately 6 kg had a ventral abdominal swelling. The lamb had been inadvertently frozen, within 2 hours of death, rather than refrigerated so was thawed for necropsy. The lamb had a soft ventral swelling between the umbilicus and the scrotum. On reflecting the skin, the swelling was found to consist of wet, somewhat oedematous dark red tissue (Image 3).
Laboratory Findings
CASE 1. Histopathology revealed severe lytic and coagulative necrosis, haemorrhage, oedema, emphysema and bacterial proliferation in the subcutaneous tissue (cellulitis). There was also evidence of peritonitis, with emphysema, oedema, coagulative necrosis and bacterial proliferation within the small intestinal serosa and abdominal wall tissue. These changes were suggestive of Clostridial infection. As Cl. septicum was grown on anaerobic culture these findings are consistent with malignant oedema.
CASE 2. Air dried smears from the affected tissues revealed a profuse population of bacteria consistent with clostridia. The smears were then submitted to the Biosecurity Queensland Veterinary Laboratories, Coopers Creek, QLD and were found to be fluorescent antibody positive for Cl. septicum and negative for Cl. chauvoei, Cl. novyi type B and Cl. sordelli. As the tissues had been frozen, samples were not submitted for histopathology.
Image 1. A male Dorset lamb with marked subcutaneous ventral tissue swelling
Image 2. The lamb above with skin reflected
Image 3. The lamb from case 2 with skin reflected
Discussion
Acquired neonatal infections are usually a minor cause of perinatal lamb mortality in lambs born under extensive conditions in Australia. Hughes et al. (1964) necropsied 6,266 lambs from the Oberon, Orange and Monaro districts from 1961-63. They examined a sample of lambs that died before, during or in the first week after birth and found infective agents in 104 of these. Cl. septicum was found in three, presumably before marking. Dennis (1974) who necropsied 4,417 lambs from 695 farms in the agricultural region of Western Australia, found that bacterial infections either caused or contributed to the deaths of 7.6% of these lambs. He cultured 18 species of bacteria plus the contagious ecthyma (orf) virus from 334 lambs with gross evidence of a neonatal infection. Cl. septicum was isolated, as a sequel to lamb marking, on 20 occasions.
Most of the clostridial bacteria that cause malignant oedema including Cl. septicum are common inhabitants of the environment and the gastrointestinal tract (Constable et al. 2017). At least some of these lambs were born in a shed increasing the risk of environmental contamination. Colostral antibodies would be expected to confer at least some immunity. The ewes in case 1 had been vaccinated with a clostridial 5-in-1 vaccine (including Cl. septicum) pre-lambing although the owner was unsure that the vaccine had been stored correctly. The ewes in case 2 had not been vaccinated. Following the diagnosis both owners intend vaccinating with a clostridial vaccine pre-lambing and plan on using umbilical disinfection for lambs that are born in sheds.
References
- Constable PD, Hinchcliff KW, Done SH and Grunberg W (2017). Veterinary Medicine, 11th Edition, pp 1428-1430
- Dennis SM (1974). Perinatal lamb mortality in Western Australian. 4. Neonatal infection. Australian Veterinary Journal, 50, pp 511-514
- Hughes KL, Hartley WJ, Haughey KG and McFarlane D (1964). A study of perinatal mortality of lambs from the Oberon, Orange and Monaro Districts of NSW. Proceedings of the Australian Society of Animal Production, 5, 92-99