Scrapie
Scrapie (classical)
If you suspect you have found a transmissible spongiform encephalopathy in New Zealand, call 0800 99 66.
Scrapie is one of a group of brain wasting diseases known as transmissable spongiform encephalopathies (TSEs). The group includes bovine spongiform encephalopathy (BSE) in cattle and chronic wasting disease (CWD) in deer.
Scrapie has been recognised in Europe since the mid-18th century and occurs worldwide. Only a few sheep producing countries (New Zealand, Australia, South Africa and Argentina) are widely recognised to be free from the disease. The disease has spread by international movement of breeding sheep from infected countries. It was introduced by that means (sheep from the UK) to New Zealand and Australia in 1952. The disease was eradicated by depopulation of infected and in-contact flocks and four year quarantine of affected properties.
Clinical signs
Scrapie is insidious in its onset. Exercise tolerance is reduced and the gait unsteady. Affected animals drink small quantities of water frequently and urinate abnormally, passing small quantities of urine. Pruritus (itchiness) is common (though not present in all cases) and animals rub or nibble themselves in an attempt to relieve the irritation, causing loss of wool. Rubbing the back commonly stimulates a nibble reflex. Animals may be nervous or aggressive and may separate from the flock. Hypersensitivity to sound or movement may be seen. Muscular twitches or tremor may occur. Ataxia of the hind limbs is a major feature. Sometimes animals will hop or trot. Some animals, however, are found dead without apparently having shown any of those signs. (This was the case with the animals that died of scrapie during quarantine of sheep imported into New Zealand from the UK in 1972.)
Diagnosis
The presenting clinical signs usually suggest the possibility of a neurological disease. Confirmation can be made by microscopic examination of brain tissue for neuronal vacuolation and other pathological changes. MAF's National Centre for Disease Investigation acquired the "Prionics" western blot test for TSEs in 2000. This test has the advantage that it can be applied to brain samples which are not fresh enough for microscopic examination.
Cause
Scrapie, as with other TSEs of animals, is caused by infectious agents of uncertain nature known as prions. Infected neurones contain accumulations of an abnormally folded form of a normally coded protein (prion protein, PrP) which is infectious and is partially resistant to protease. No DNA has been demonstrated though, in many respects, such as strain variation and mutation it behaves as if a genome were present. The agent is unusually resistant to most forms of disinfection.
Transmission
Scrapie is contagious. Lateral transmission occurs naturally, possibly by consumption of or exposure to infected placentas. Scrapie may also be transmitted from an infected ewe to her lamb through the milk.
Effects of introduction
Introduction of scrapie could have adverse effects on the export of live breeding sheep and embryos. Meat exports would probably not be affected, but the developing biopharmaceutical industries could be severely affected. The cost of any control programme likely would be a considerable.
Risk of introduction
Scrapie would only be introduced by the importation of live sheep from countries where the disease occurs. New Zealand policies permit the importation of sheep embryos and semen, as accumulated scientific research has shown that these commodities are unlikely to transmit scrapie. Nevertheless, importation is via a rigorous quarantine process.
Control
Any diagnosis of scrapie would almost certainly result in quarantine of the entire sheep or goat flock in which affected animals were found. Further action would depend on the results of epidemiological investigation to determine the extent of the problem and consultation with the sheep industries over their willingness to embark upon a control programme. Destruction of affected flocks and in-contact flocks was the policy followed in the early 1950s when the disease was introduced by sheep imported from UK. Though expensive, it was effective.
Also see the TSE Surveillance page for information about Surveillance programmes and incentives.
Page last updated: 28 October 2009
