On the lookout: sheep with neuro signs
Author: Dr Paul Beltz, Senior Veterinary Officer, Agriculture Victoria
Transmissible spongiform encephalopathies (TSEs) are diseases of animals that cause a variety of nervous signs, which are particular to that disease in that species. Scrapie is the sheep TSE, just as bovine spongiform encephalopathy (BSE, or ‘mad cow disease’) is the TSE of cattle, and kuru (which is spread by cannibalism) was a TSE of humans on Papua New Guinea. All TSEs are thought to be spread by eating part of an infected animal, including meat and bone meal.
Australia remains free from TSEs, a status that is monitored and maintained through the National TSE Freedom Assurance Program (NTSEFAP). Part of the NTSEFAP is to test a number of animals exhibiting signs typical of a TSE every year.
Scrapie gets its name from the itchiness it produces in affected sheep — they scrape along walls and fences, just like sheep with lice. Affected sheep can show behavioural and gait changes, such as bunny hopping, or trotting with the forelimbs. They may have a tremor and show weight loss. If sheep have scrapie, they usually die within six weeks of the first signs appearing.
If you have an adult sheep showing any of these signs, they may be eligible for testing under the NTSEFAP, with the associated subsidies (see box right). Each year, about 110 sheep are examined under the NTSEFAP in Victoria, and about 600 across Australia. As well as ruling out scrapie, a full laboratory workup can be done to determine the actual cause of the neurologic signs. Commonly occurring conditions found during examination of sheep for TSEs in Victoria, include hypocalcaemia and pregnancy toxaemia, polioencephalomalacia (vitamin B1 deficiency) and plant poisonings. Listeriosis is a particular bacterial infection that affects sheep (and cattle), often causing a head tilt and circling gait (it also causes abortion in ewes). A number of other bacterial infections are sometimes seen, as well as sheep with lice.
We have found several cases of atypical scrapie, a non-infectious, spontaneously occurring TSE of sheep that occurs in every population in Victoria at an extremely low frequency. This demonstrates that this program is working very well, as it is finding these cases that occur at very low rates but have identical clinical signs to the exotic scrapie.
The National Transmissible Spongiform Encephalopathy Surveillance Program
The National Transmissible Spongiform Encephalopathy Surveillance Program (NTSESP) demonstrates Australia’s ongoing freedom from bovine spongiform encephalopathy (‘mad cow disease’) and scrapie. The NTSESP involves detailed examination of several hundred sheep and cattle nationally every year. Individual animals identified as eligible candidates for inclusion in the program must meet several specific criteria:
- Sheep must be at least 18 months of age.
- Cattle must be at least 30 months of age and no more than nine years of age.
- The animal must be displaying progressive clinical neurological signs (e.g. circling, blindness or abnormal behaviour).
- The animal must be alive at presentation to a veterinarian or Agriculture Victoria staff.
- A producer incentive of $100 for sheep and $300 for cattle is available (as well as incentives for the private veterinarian investigating), and a maximum of two animals per property is permitted each year.
How to get involved
Producers can become involved in the program by reporting their own animals that fit these criteria to their local veterinarian or by contacting their local Agriculture Victoria Animal Health staff or by calling the Customer Call Centre on 136 186View animal health contacts
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