April 23, 2014

New Zealand agricultural history. No 2. Importing exotic sheep breeds

Scrapie in UK
Cause of Scrapie
Scrapie history in New Zealand

By Dr Clive Dalton

Scrapie was a major importation risk and this certainly worried a lot of people both in New Zealand and in UK.  

Scrapie in UK
Scrapie is endemic in UK, and we budding young shepherds used to see what must have been the disease in Cheviots and Scottish Blackface sheep on my native Scottish Border. Sick sheep used to act a ‘bit daft’ and scrape their wool off by rubbing against stonewalls and fences – hence the name. but no farmer would ever have dreamed of getting a vet to look at a sheep – they would have cost money!  Scrapie wasn’t common in UK, but it has a fearsome reputation for countries like New Zealand that want to claim a ‘clean health’ status, especially for exporting animals. 

(See Wikipedia for full details of Scrapie).

In the UK in recent years a testing programme was undertaken to eliminate Scrapie from the Swaledale breed, so it must have been serious enough to go to all the work and cost involved. 

 In the past, it was not easy to diagnose, as it required slaughter and examination of brain tissue. Brains are still examined today but there are now other fancy DNA diagnostic tools that can be used.

 Picture shows Swaledale ewes in their native Swale dale in Yorkshire, England

Cause of Scrapie
The organism causing Scrapie is a prion, which is a protein, and is most commonly spread from ewe to lamb at birth in all the birth fluids and close contact although a lot of this is still a mystery.  A prion has no DNA and multiplies by simply duplicating itself like the growth of a crystal.

The problem with Scrapie is that it develops slowly and is usually only seen in sheep around 3-5 years of age. So this is the challenge for quarantine which consequently has to go on for years, and greatly increases the cost of importations and especially if in the end, animals have to be slaughtered.

So nobody would risk buying sheep (or goats which can also carry Scrapie) from New Zealand if it was ever shown to become endemic here.

It’s always easy to show that a country has a disease; the hard part is proving that it has been eliminated with a high level of guarantee.  New Zealand’s trading competitors love this and just keep on demanding more data before they will relax their import regulations for New Zealand produce.  We live with this as a daily threat.

Scrapie history in New Zealand

This photo tells a bit of important history in the study of Scrapie.  

Dr R.H. Kimberlin who is the world authority on such diseases visited New Zealand and Alan spent time with him.  He was a valuable resource to check diagnostic criteria on such diseases.

Kimberlin edited the 'bible' on the subject. See reference below:
'Slow virus diseases of animals and man'.  New Holland Research Monograph, Volume 44.

Photo:  Dr Kimberin standing, Alan Julian at microscope.  Photo by Alan Julian

Veterinary pathologist Alan Julian gave a paper in 1996 to a workshop in Australia on a range of nasties called ‘spongiform encephalopathies’ in domestic animals where he reported the Scrapie saga in New Zealand.  Here are the key points:
  •  Scrapie was diagnosed for the first time in New Zealand in June 1952 in two Suffolk sheep in Canterbury imported from England in 1950.
  • Farm was quarantined and all sheep on property were destroyed.
  • All sheep sold from this property in the previous 3 years (a total of 225) were traced. (Presumably they were sent to the meat works).  
  • The farm was restocked 4 weeks after slaughter. 
  • Control measures were not effective as in 1954 an outbreak in Southland in a South Suffolk ewe was traced back to the Canterbury property.
  •   Control measures for this outbreak involved 191 properties, with the slaughter and burial of 4,399 sheep. (Presumed they were sent to the meat works).  
  • The farms had restrictions put on them for 3 years during which time all sheep sold from the properties had to go direct to slaughter. 

No other outbreaks were ever recorded so New Zealand was declared Scrapie free.  This saga was well documented and used for veterinary teaching, and it made the profession very determined never to allow it into NZ again!

Picture of Suffolk sheep - the breed that brought the Scrapie to New Zealand from England in 1950.

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