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CASE NOTES


Failure of Innoculation (Scabigard, Zoetis) to Prevent Scabby Mouth (Orf) in Australian White Lambs

Bruce Watt, Central Tablelands Local Land Services, Bathurst and Kelly Graham, Zoetis

Posted Flock and Herd June 2024

Introduction

Scabby mouth (orf, contagious ecthyma or contagious pustular dermatitis), is a disease caused by a parapoxvirus and affects sheep, goats and occasionally people. Infection occurs through damaged skin, most commonly to the lips or feet. The virus is highly resistant and can survive in the environment for more than one year. Scabby mouth occurs most frequently in young lambs but is occasionally seen in older sheep. Lambs grazing thistle-infested pastures or coarse stubbles are particularly susceptible to infection, as are lambs that are being supplementary fed in shared feeders. There is no specific treatment for scabby mouth so when farms are known to carry the disease it is best managed by vaccination. A live vaccine is administered by skin scratch on a protected site, usually in the axilla inside the foreleg, producing a mild and controlled form of the disease (Scabigard®, Zoetis).

History

In June/July 2023, a Central Tablelands livestock producer marked 600 May/June-drop Australian White (AW) and Dorper lambs. At marking the lambs were inoculated against scabby mouth (using Scabigard, Zoetis). In mid-November the owner noticed that lambs in one mob of 110 mixed-sex AW lambs had symptoms of scabby mouth. These lambs were running in a paddock infested with saffron thistles (Carthamus lanatus) that had been sprayed with a broadleaf herbicide (Lontrel/MCPA). Lambs in the other mobs, running in paddocks less infested with saffron thistles, were not affected.

The owner reported that in the mob of 110 affected lambs, 40% were mildly affected while 10% were severely affected.

Clinical findings

A sample of affected lambs was examined on 27 November 2023. Of the eight well-grown 35-45 kg lambs in the yard (Image 1), five were severely affected with swollen, crusty, bleeding lesions on the upper and lower lips and skin around the nares. No lesions were noted elsewhere on the body.

Image of white lambs with crusty noses
Image 1. The sample of eight lambs including five severely affected lambs
Image of white lamb with bloody nose
Image 2. Closeup of a severely affected lamb. This lamb was sampled for virus detection.

Laboratory findings

On 27 November 2023, samples of scab material from the lips of one severely affected lamb (Image 2) were submitted to EMAI Menangle with the aim of confirming orf infection. The samples were reported as positive for orf using negative staining electron microscopy.

FOLLOW UP

The owner was highly experienced both as a sheep owner and lamb marking contractor. He was aware of good vaccination technique and adhered to vaccine storage requirements. He had not seen this problem before.

Discussion

The cause of this vaccine failure, (assuming that the vaccine was stored and used correctly), was likely due to a combination of heavy virus contamination in the paddock and a heavy thistle infestation causing damage to the skin and mucous membranes. In situations such as this one, scabby mouth can still occur in correctly vaccinated flocks, but the resultant lesions should be less severe, impact fewer sheep and resolve more readily than those affecting unvaccinated flocks.

Given the viral contamination on this property, continued vaccination is recommended to minimise any economic impact of this disease in the future.

Zoetis Guide to the Implementing an Effective Scabby Mouth Vaccination Program
Scabigard is a modified live vaccine and therefore needs to be handled and stored correctly (according to the label) to ensure the vaccine remains efficacious. Any vaccine not used on the day of vaccination should be discarded and dips, disinfectants or other chemicals should not be applied to the scratched area (or on the applicator).
While it may not always be practical, a sample of vaccinated sheep or lambs should be examined 10-14 days after vaccination. There should be a continuous line of scabs visible along the site of the scratch made on the skin. This lesion is indicative of successful vaccination and referred to as a 'take'. Failure to show evidence of a 'take' may indicate problems with vaccination technique or handling of the vaccine, resulting in loss of potency. Re-vaccination of animals should be considered where a 'take' is not evident.
The following checklist provides a guide to an effective Scabigard vaccination program

 


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