What is scabby mouth?
Scabby mouth is a viral disease of sheep and goats that causes scabs and pustules, usually around the mouth and face of affected animals. It is also known as contagious pustular dermatitis, contagious ecthyma or orf.
Which animals are most at risk?
Scabby mouth can occur in sheep of any age but is most common in lambs and weaners over summer. Older sheep tend to be immune as a result of previous contact with the virus.
Causes of scabby mouth
The scabs shed from infected sheep onto pasture and in yards can be infectious to other sheep for many years. Some sheep may also carry the virus and infect other sheep.
Animals become infected with scabby mouth when abrasions in the skin allow the virus to enter and establish. Outbreaks are often associated with abrasions caused by rough dry feed, such as stubbles, thistles, grass seeds or burrs. Infection may also occur if there is prolonged wetting of the feet.
Signs of scabby mouth generally appear about three days after infection.
Signs of scabby mouth include:
- raised scabs with a red ulcerated area underneath the scab around the:
- lips, muzzle and nostrils (most commonly)
- eyes, feet, lower leg, anus, vulva, udder, scrotum and pizzle (less commonly).
The scabs may occur as single scabs or packed-together scabs that form large wart-like lesions.
Signs of early infection are not usually seen but can include redness, slight swelling of the skin, watery blisters and pustules which quickly rupture to form thick brown scabs.
In severe cases, lesions can extend into the nostrils and mouth and cause the affected animal to stop eating.
Sheep with feet lesions may become lame and ewes with udder lesions may develop mastitis. Flystrike may occur, particularly when feet are affected.
How a veterinarian can help
Most producers can diagnose an outbreak of scabby mouth based on the signs listed.
Where producers do not know the cause of lesions or see unusual lesions, they should contact a veterinarian to investigate whether scabby mouth or another disease is occurring. Laboratory testing of the scabs can identify the virus.
No specific treatment is available for scabby mouth but generally affected animals recover spontaneously with scabs healing in about 3–4 weeks.
Try to determine what is damaging the skin and allowing the virus entry, and remove the source. Where harsh dry feed is a problem, provide sheep with a softer, more palatable feed.
It is also important to monitor animals for flystrike and secondary infection.
If scabby mouth is occurring regularly in a feedlot, consider either starting a vaccination program or moving the feedlot to a new site.
While animals infected with scabby mouth usually recover uneventfully, it is particularly important to ensure animals being supplied for export do not have scabby mouth (see below).
Animals previously infected with scabby mouth develop immunity provided there is regular exposure to the virus.
A live vaccine which introduces a controlled volume of live virus to the sheep is available to protect against scabby mouth. To apply it, scratch the bare skin on the inside of the leg or brisket with a special applicator. Follow the vaccine manufacturer’s recommendations carefully as correct vaccination technique is important for development of protective immunity.
The vaccine produces a ‘take’, a small row of pustules that appears along the vaccine scratch line, mimicking natural infection.
Note: The scabs produced by the vaccine can infect non-immune sheep and people. When vaccinating lambs it is advisable to vaccinate all lambs in the mob at the same time. People should avoid contact with the scabs and cover all cuts and abrasions before handling animals and wash hands and clothes thoroughly after handling.
Immunity following vaccination develops within two weeks. Once immunity has developed, vaccinated sheep are protected for 12 months. They may be susceptible to infection but the disease is mild and short-lived.
If sheep are continually re-exposed to low levels of virus in the environment, the immune system can provide protection for several years.
The vaccine is generally given to lambs as older sheep are considered to have immunity. Do not vaccinate ewes less than six weeks before lambing as the vaccination scabs may provide a source of infection for lambs. Complete vaccination at least eight weeks before shearing as the scabs falling off the vaccination site can infect shearers.
Animals for export
Scabby mouth is a significant disease for live export. The concentration of sheep for backgrounding and shipping for live export allows rapid spread of the disease if it is present. Trading partners may reject consignments of sheep with scabby mouth. Ensure sheep are vaccinated and immune to scabby mouth before selling for live export.
Scabby mouth and human infection
Scabby mouth is a zoonotic disease (an animal disease that can infect humans). In humans, swollen red nodules with a greyish centre leading to scabs may develop on the skin a few days after infection. These should lift and the skin heals in about two weeks. Seek medical advice if necessary.
Note that shearers may refuse to handle infected or recently vaccinated sheep.
Diseases that may look like scabby mouth:
- lumpy wool (dermo)
- footrot (if feet lesions involved)
- bluetongue disease (exotic to Australia)
- foot-and-mouth disease (exotic to Australia)
- sheep pox (exotic to Australia).
Producers play a vital role in the early detection of exotic diseases in Australia. If you see unusual disease signs, abnormal behaviour or unexpected deaths in your stock, ring your local veterinarian, DPIRD veterinary officer or the Emergency Animal Disease hotline on 1800 675 888.