CASE NOTES
A case of Salmonella in lambs
Nik Cronin, District Veterinarian, Lachlan Livestock Health and Pest Authority, Forbes
Posted Flock & Herd March 2011
Introduction
In early December 2010 a farm manager in the Forbes district rang regarding deaths associated with scouring in lambs. He was working for a company which was purchasing large numbers of lambs to finish on lucerne. They had almost completed their buying, acquiring around 10,000 lambs over the previous six weeks. They were sourcing off farm through an agent in lots of 500-1,000. Animals were being stored in one of two holding paddocks of lucerne on arrival before being shorn, vaccinated and drenched with a 3-way product and finally transported to a fresh lucerne paddock. The available water source in the holding paddocks was a trough.
This particular morning there were 15 dead animals in the sheep yards. This mob had arrived 1 week ago and were shorn but had not yet been vaccinated or drenched. The dead animals had evidence of a green, mucoid scour. There was another approximately 30 animals in the mob with this scour and many of these seemed depressed.
The manager commented that he had also had 15-20 deaths in a separate mob one week ago with similar type of scouring also noted. The losses stopped after a couple of days and they had put these down to complications from the unseasonal wet weather conditions at the time.
Post-mortem
An animal that had died within 10 minutes was selected for post-mortem. Rectal temperature was 40.9 degrees Celsius and there was evidence of mucoid, green scour. Oral mucous membranes were dark purple. The entire lungs were light purple and the tip of the right accessory lobe was collapsed. A small number of 15mm long fine white worms were located in the middle airways and there was some clear mucoid fluid associated with these. The entire liver was dark purple and oozed blood from the cut surface. Both kidneys were soft and dark purple. They bulged slightly and oozed blood on the cut surface.
The entire serosal surface of the abomasum and intestines was dark purple. The abomasal mucosal surface was slightly hyperaemic and there were pin point haemorrhages scattered diffusely across. The proximal duodenal wall was slightly thickened, approximately twice normal and dull. The middle to distal ileum had pin point haemorrhages scattered across the mucosal surface. The distal ileal wall was also thickened 3-4 times normal. There were also pin point haemorrhages scattered diffusely across the caecal mucosal surface and 30-50 whip worms present.
The morphologic diagnosis was severe acute bacterial and parasitic enteritis.
Case management
Samples were collected and submitted primarily for histopathology and culture but with a high index of suspicion of a bacterial cause a direction was given to start treatment with antibiotics. A script was written for oxytetracycline 200mg/ml to be given at a dose rate of 1ml/10kg to treat lambs that were scouring or depressed. The manager was also advised that many conditions that caused scouring in livestock were zoonoses and that he and anyone under his charge handling the sick animals should pay attention to hygiene and hand washing, and to avoid contact in particular with the faeces.
Pathology findings
Histopathology results confirmed the presence of an enteritis consistent with a bacterial cause with changes present in the abomasum, duodenum, small intestine, large intestine and mesenteric lymph node as evident on gross pathology.
Selective enrichment culture for salmonella on the gut content was positive, and the organism was further identified as Salmonella typhimurium.
No egg count was performed on the submitted faeces. A worm burden was certainly expected as there was already visible evidence of lung worm and whip worm on post-mortem, however the lambs were to be drenched with a combination product regardless. In retrospect it would have been interesting to see either a faecal egg count or total worm count result.
Follow up
Approximately 25 scouring or depressed animals were treated with antibiotics. A further 10 animals died despite treatment. By the time laboratory results were returned the losses had stopped and the remainder were drenched and vaccinated and put onto fresh lucerne. They had finished purchasing sheep so the likely contaminated holding paddocks and shed area would be unused for several months.
Discussion
Detection of salmonella infection in food production animals is of particular importance because of the risk of transmission of disease to humans. Humans may be infected by directly handling infected animals or by the consumption of contaminated food products [7] Salmonella typhimurium is the most frequent serotype which causes disease in both humans and a variety of animals [8] and is the second most common food borne pathogen in human beings [9]
At current sheep prices the loss of 40-odd head represents reasonable economic loss. There are several factors which likely contributed to the development of this outbreak. The stress of transport is likely to have weakened the immune system initially. The two holding paddocks utilised were heavily stocked. They had held several different lots of lambs in the previous 6 weeks and were heavily contaminated with faeces. They were well eaten out and may not have provided adequate nutrition for the processing period.
Unseasonal falls of rain had left puddles of water and general damp conditions under foot which are favourable for survival of salmonella organisms. Evidence of lung and intestinal worms at post-mortem suggests there was poor drenching history. A likely high worm burden and subsequent reduced gut health is also likely to have contributed to this outbreak.