What Is Scabby Mouth Disease And How Is It Spread?

Scabby mouth is a viral disease affecting sheep of all ages.  The virus enters sheep through damaged skin generally caused by contact with thistles, hay, coarse pastures and stubbles.  Feedlot environments and the use of pelleted feed will also predispose to the virus development.  The most common form of disease spread is via a previously infected animal.  The virus can survive in the wool and on the skin of these animals for a long time.  The movement of animals from property to property has had a major impact on the disease spread throughout New Zealand.


The virus can survive in the environment for many years under ideal conditions.  Shearing sheds, watering points, feed troughs and sheep yards are the most common places for sheep to become infected with the virus.


Clinical signs of the disease may vary within age group of sheep.  Scabs appearing on the mouth and lips are particularly common in lambs.  The nostrils, teats and udders, the poll of rams and the feet are the other commonly affected areas.


The disease is extremely efficient at gaining entry into the animal; all sheep are potential targets.  Lambs are the group of sheep most at risk.  The scabby mouth disease cycle is approximately 4 to 5 weeks for completion.  During this time there are a number of stages up and until the scabs fall off.


What Effect Does Scabby Mouth Disease Have?

The lesions resulting from infection although only temporary can severely restrict the growth rate of lambs with obvious financial penalties resulting.  Repeated failure to prevent scabby mouth disease in lambs could also be considered an animal welfare issue and result in action being taken by the authorities.


Should I Vaccinate With Scabby Mouth Vaccine?

You should only use scabby mouth vaccine where:-

*     You encounter an outbreak of the disease.

*     The vaccine has been routinely used on the property in the past.


This is because the strain used in the vaccine is what is known as non-attenuated and the scabs resulting from correct vaccine use when they drop off introduce the virus onto the farm - effectively forever.


Which Sheep Should I Vaccinate?

On nearly all properties it is young lambs in their first summer that are most susceptible.  If your property fits the requirements above, then all lambs should be vaccinated at the first convenient opportunity, which is at tailing.  It is important to vaccinate each years lambs at this time.  Repeated contact with the virus in the soil, on other animals etc provides a boost to the immunity provided by the vaccine giving the perception that one vaccination gives lifetime protection.   Hence the practical end result is an apparent lifelong immunity.  There are a small number of specialised instances when vaccination of older sheep may be appropriate - for example, following the sale and movement of older sheep from a clear to an infected farm.  Contact your vet for advice in these specialised cases.


Where And How Do I Apply The Vaccine?

Almost any area of bare skin is appropriate for scabby mouth vaccination.  The recommended site is inside the front leg or on the side of the brisket.  Vaccination will produce a “mild” controlled form of the disease at this  protected site and will avoid possible cross contamination with other livestock.


The groin area is also suitable unless using fly or wound dressings.  These products could result in the vaccine being washed off or inactivated.


The scratch needs to be firm and penetrate the outer layers of skin and grease, but avoid drawing blood which may harm or wash the vaccine away.  The length of the single scratch should be 4-5cm.  A blue dye has been added to the vaccine to help you see if it has been applied correctly along the full length of the scratch.


The method described above is the only recommended method of vaccination.


What Protection Can I Expect Following Vaccination?

Scabby mouth virus is a pox virus.  Pox virus vaccines do not provide 100% protection against challenge.  In practice this means that if a correctly and well vaccinated flock is exposed to a very heavy challenge such as mixing them with a number of heavily infected animals or exposure to a heavily contaminated environment with conditions conducive to infection such as large number of thistles etc then lesions can occur in vaccinated animals.  These lesions however are much less severe and resolve more quickly than those on previously unvaccinated animals.


What Other Precautions Do I Need To Take?

i) Read the product leaflet before commencing vaccination.  First time users should have a short consultation with their veterinarian.  There is also a video available demonstrating the correct usage of the vaccine.

ii) As the vaccine is a living virus, care should be taken when handling the product to avoid scabby mouth infection in humans, which is known as Orf.  Ensure all cuts and abrasions are well covered.

iii) Correct storage of the vaccine is also important because it contains live virus.  Keep the vaccine at 2-8oC - refrigerate but do not freeze.  Store away from food.  Take only enough vaccine out to cover the days requirements and keep out of direct sunlight - preferably in a chilly bin.

iv) Check the prongs of the applicator regularly for good vaccine flow.  Hair, wool and grease build up can prevent vaccine flow and needle penetration.


Is There Anything Else I Need To Know?

Yes, following vaccination it is important to check for “takes”.

What is a take?  A take will develop along the live vaccination appearing as inflamed raised blisters whitish in colour surrounded by a reddened zone before developing into scabs.  This results in the controlled development of scabby mouth (which does not spread beyond the vaccination site) to give sheep immunity.


To be sure the job has been completed satisfactorily, especially for first time users and where contract tailing gangs have been employed it is recommended that you check for takes.  A cut of 20 lambs should be checked 7-14 days after vaccination.  Small takes over only part of the scratch are indicative of poor technique as is the brown line of a healing scratch.