CASE NOTES
Severe tongue lesions in lambs consigned for slaughter prompting an omagod moment, the lesions were consistent with orf infection and foot-and-mouth disease was ruled out
Jeremy Rogers, Senior Veterinary Officer, PIRSA, Murray Bridge, SA and Jemma Hassam Veterinary Officer, PIRSA, Naracoorte
Posted Flock and Herd September 2025
INTRODUCTION
In early September 2024 an alert DAFF Veterinarian working at a processing plant in South Australia noticed a consignment of lambs with unusual nose and tongue lesions. He became alarmed when several lambs in the consignment with these changes were observed and called the Emergency Animal Disease (EAD) hotline number to report his findings.
Foot-and-mouth disease (FMD) can be difficult to diagnose in sheep because clinical disease is often mild and because common endemic diseases of sheep, such as orf, are similar in appearance. Trauma can also cause lesions to the dental pad, upper and lower gums, and the tongue. In the 2001 FMD outbreak in Britain, the differential diagnosis of FMD was further complicated by the detection of oral lesions of unknown aetiology, colloquially and most appropriately known as Ovine Mouth and Gum Obscure Disease (OMAGOD) (Watson 2004).
HISTORY
Four-hundred lambs were sent direct to slaughter from a property in the upper south-east to a processor in Adelaide on 4 September 2024. No salivation, lameness or illness was observed ante-mortem, but at slaughter 20/400 were observed to have severe tongue lesions. Some also had muzzle lesions, but no foot lesions. Samples were collected by the On-Plant Veterinarian (OPV) and stored in a refrigerator, who contacted PIRSA for instructions via the EAD hotline number. The following day a further 600 lambs were processed from the same property. Mouth lesions resembling elevated plaques were seen in some lambs and there were some lesions on the muzzle.
Following notification by the OPV, Primary Industries and Regions South Australia (PIRSA) directed collection of samples to test for FMD. Negative results for FMD were initially reported from the local laboratory on 6 September 2024, later confirmed by the Australian Centre for Disease Preparedness on 9 September 2024. Enquiries at the property of origin in the upper south-east of South Australia revealed that no abnormal disease processes had been noted in the lambs recently, and other risk factors such as overseas visitors and livestock introductions were ruled out as sources of FMD virus. There were about 3000 sheep on the property, all apparently healthy. No foot lesions were seen. The lambs consigned to slaughter had been grazing lucerne pastures with supplementary lick feeders. Hay and straw had also been provided. The animals were also reported to be up to date with standard clostridial vaccination. No recent drenching had been performed.
GROSS AND LABORATORY FINDINGS
Further testing on the samples to obtain a diagnosis was not performed after FMD was excluded but the lesions on the lips of affected lambs were characteristic of contagious ecthyma ('scabby mouth/ orf'). Physical abrasions/ local infections from penetrating foreign bodies, and possibly photosensitisation were other differential diagnoses.
Figure 1. Tongue ulcers and papules
Figure 2. Ulcers on the tongue
Figure 3. Papules on the tongue.
Figure 4a. Lesions on the lips and elsewhere on the face that are typical of orf infection
Figure 4b. Lesions on the lips and elsewhere on the face that are typical of orf infection
DISCUSSION
Orf, also known as contagious ecthyma or scabby mouth, was the most likely cause of the lesions in this case. Orf presents primarily as tongue lesions, and these would most likely be missed on farm. The fact that these lambs were presented for slaughter indicates that the lesions may not have had a significant impact on growth rates.
Sporadic oral lesions in sheep have been noted and observed at processors. There have been some well-documented studies in New Zealand (Black H, Evans MHD, Stone MA and Julian AF, 2004) and the United Kingdom (Watson P 2004) discussing the appearance and causes of these lesions. Another study by the Department of Primary Industries in Victoria in 2006 and published as a booklet, describes lesions and observations in Victoria by season. In this study, most lesions were attributed to grass seed or other forms of oral trauma, particularly in younger sheep.
When a major outbreak of FMD occurred in the UK in 2001, it was observed that sheep presented for slaughter with oral lesions due to FMD may have been difficult to distinguish from sheep affected with other common conditions. Although lameness due to FMD and erosions / pathology in the feet of cattle and pigs is most often obvious, foot lesions due to FMD in sheep and goats are usually not as severe. Therefore, observations of mouth lesions in sheep are always of interest in Australia, especially where multiple animals from a single source are affected.
The main differential diagnosis for these lesions in addition to orf was trauma followed by local infection.
In South Australia, a common weed species called Caltrop (Tribulus terrestris) produces sharp, hard spines in the seeds that can puncture gums and tongues when consumed and other varieties of grasses with hard seeds can also cause trauma to the mouth and tongue.
Scabby mouth is also common and can rapidly spread in flocks that are unvaccinated or naive, including when sheep are sharing lick feeders. This virus infects sheep via damaged skin or mucosa, typically around the mouth, nose and occasionally feet, teats (in ewes with suckling lambs) and even ears from puncture wounds caused by ear tags.
Another possible cause of the lesions in this case was photosensitisation. It typically occurs in South Australia in September/October when lambs graze fast-growing, short, green pastures. A major outbreak affecting an estimated 30,000 sheep in South Australia was described in 2017 and associated with lambs grazing legume and other crops infested with cow pea aphid. The photographs in figures 1-5 show lesions that could be seen with any one of these differential diagnoses.
A PIRSA veterinary officer attended the property of origin to discuss the laboratory results, show photographs of the lesions to the owner and discuss potential causes. It was agreed that the most likely cause of the tongue lesions was trauma from lick feeders, which then allowed infection with scabby mouth. No vaccination against scabby mouth had occurred on this property. No lambs or sheep with visible muzzle or mouth lesions of scabby mouth were seen during the property visit. When leaving the property, the PIRSA veterinarian also noted that some large tree stumps had been pulled from the ground and were left in the paddock. Some lambs in that paddock were observed chewing on the roots of the trees. This behaviour could have been another source of oral trauma. Although a definitive diagnosis of the lesions in this case was not established, the most likely explanation would be scabby mouth lesions arising from oral trauma due to plants or the lick feeders on this property.
A positive outcome of this investigation was a meeting between a PIRSA veterinary officer and some new OPV staff at the processor. This meeting provided an opportunity to describe how EAD responses are handled in South Australia in both the alert, standby and response phases, the impacts on processors of these events and who makes important decisions. Clear and open lines of communications are vitally important to the industry. OPVs need to know about how to report incidents and the support they will get from PIRSA following reports.
The lesions seen in this case were remarkable and provided an interesting case for testing the EAD arrangements in place at both PIRSA and processors. These cases assist in building relationships with stakeholders that would be vital during an emergency response.
REFERENCES
- Watson P (2004) Differential diagnosis of oral lesions and FMD in sheep In Practice 26 182-191 onlinelibrary.wiley.com
- doi.org
- Black H, Evans MHD, Stone MA and Julian AF (2004) Lip and gum lesions in sheep at two abattoirs in New Zealand New Zealand Veterinary Journal Volume 52 -Issue 2
- Watson PJ, Scholes SF and Smith RP (2006) Characteristics, prevalence and aetiology of lesions of the oral mucosa in adult sheep Veterinary Record First published: 20 May 2006
- Ovine Mouth Pathology in Victoria, Australia. DPI Victoria Specialty press, Albury, NSW, 2006