WITH THE recent launch of a new version of the only orf vaccine available, it is important for sheep owners to recognise the problem early on and manage it accordingly, as well as recognise the effects the virus can have on humans.
It is essential to remember the virus is highly contagious and spreads rapidly, Peter Nettleton of the Moredun Research Institute told producers attending a Moredun/Schering-Plough meeting at Plumpton College, East Sussex.
“The scabby lesions found on the mouth and nostrils of a sheep can survive year on year providing they are kept dry. This is particularly the case with flaky scabs situated across the sheep’s poll and ears.
“Sores can be mild, but they may also spread to other sites. Rapidly growing lesions may develop on gums, palate and tongue, as well as lips, feet and lower limbs.”
Dr Nettleton told producers the reason that orf is such a tricky virus to prevent and control is the group of poxvirus it belongs to.
With its poor immune response vaccination is difficult and offers only short-lived protection. “Much work has been done to improve the currently available Scabivax vaccine and to develop a quicker and more effective diagnostic test.”
The vaccine involves scarification of the skin surface with a cell culture grown virus. “We have tried to implement an intramuscular vaccination process with a live virus but, unfortunately, that has proved unsuccessful.”
Because there is no current treatment available, treatment must be directed at preventing secondary bacterial contamination, Mr Nettleton explained.
“The level of virus challenge can be reduced by thoroughly disinfecting lambing sheds, as well as reducing the presence of abrasive material inside as well as out.”
When orf is a major problem on farm, Dr Nettleton strongly advises considering a vaccination programme.
The virus can also infect humans, so careful handling of the vaccine is required, he warned. “Scabs from vaccinated sheep will, however, contaminate the environment, so it must be used only on orf-infected farms.”
As an aid for control, the vaccine should be used three to four weeks before orf is anticipated, he said. “In practice it is usually given to ewes eight weeks before lambing and to lambs shortly after birth. It can also be used once an outbreak has started.”
Dr Nettleton also suggested flockmasters should consider vaccinating new sheep brought onto an orf- infected farm.