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New Scrapie Research indicates the possibility of a live animal test
New research from Iowa State University conducted by Jacob Petrich has discovered a non-invasive diagnostic tool to help identify sheep infected with scrapie. The eyes of the sheep infected with scrapie return an intense, almost white glow when researchers shined a blue excitation light in their eyes.
The study began as a project funded by a grant from the US Department of Defense. Petrich and his team were working in slaughter houses looking for bacterial contamination on carcasses using a fluorsecing spectroscopy device. One day they were using the device and saw the spinal cord shine through the skin with an intense light. The team of researchers began thinking about the possibility of a live test to help in the detection of transmissible spongiform encephalopathies such as scrapie or mad cow disease.
To test their theory, the researchers collected eyeballs from 73 head of sheep -- with 35 of these known positive for scrapie infection. They found that the retina of sheep eyes infected with scrapie fluoresced a very bright white light and the non-infected sheep did not.
This could be a major breakthrough in the possible development of a live animal test to diagnose scrapie. At the present time, the animal needs to be euthanized and the brain and spinal cord removed to make the diagnosis. There is supportive research that indicates the change in an animal's retina when they are affected by a neurological disease. The development of such a test would be beneficial to the whole sheep industry.
To see the whole press release from Iowa State University, go to: http://www.news.iastate.edu/news/2010/oct/TSEtest
A Producer's Guide to Scrapie
What is Scrapie?
Scrapie is a fatal, degenerative disease of the central nervous system of sheep and goats. It belongs to a group of diseases called transmissible spongiform encephalopathy or TSEs.
Some other TSEs include:
· Kuru, CJD, and variant CJD in humans
· Bovine Spongiform Encephalopathy (BSE) in cattle
· Chronic Wasting Disease affecting deer, elk, and moose.
Scrapie is characterized by the formation of holes in the cells of the brain and the accumulation of an abnormal protein, which results in the loss of nervous function.
Breeds Affected
Since its introduction, scrapie has been diagnosed in over 1,000 flocks throughout the United States. While no breed of sheep is known to be immune to scrapie, the breeds originally identified as most usually affected in the U.S. were blackface meat breeds and crosses of these breeds.
Every sheep carries a pair of genes that affects its susceptibility to scrapie. All genes are made up of tiny units called codons. Each codon determines the type and order of amino acids that form a protein. The codons that have the greatest influence on scrapie are numbered 171 and 136.
Symptoms
The name scrapie is derived from one of the classic symptoms of the condition. Some affected animals will compulsively itch and scrape off their wool against rocks, trees or fences. Not all scrapie infected sheep will rub and a few will die without showing any clinical signs. Some of the clinical signs include:
Early Symptoms
· Behavioral changes
· Apprehension or uneasiness during handling or feeding
· Tremors of the head or neck
· Movements of hind legs become uncoordinated
· Isolation from the flock
· Weight loss
Advanced Signs
· Intense itching and scraping
· Broken or pulled out wool
· High stepping or stumbling
· Grinding of teeth
· Shaking of the tail and rump
· Movements of hind legs become uncoordinated
Prevention
Producers have three management tools at their disposal when dealing with scrapie.
· Maintain a closed ewe flock – including not sharing lambing facilities
· Genetic selection – purchase rams that are genetically resistant or from a flock that is enrolled in the voluntary Scrapie Flock Certification Program
· Improvement of lambing hygiene – if possible, lamb in individual pens; placentas and soiled bedding should be removed and either incinerated or buried
Genetic Testing
A blood sample needs to be drawn by a licensed accredited veterinarian. The veterinarian will submit the sample with a VS Form 5-29 to a laboratory approved by Animal Plant Health Inspection Service.
The amino acids at codon 171 are labeled as R, Q, H, and K. R gives sheep resistance to the most common type of scrapie in the U.S. The other amino acids do not. The amino acids at codon 136 affect the susceptibility of sheep to one type of scrapie that is uncommon in the U.S. Sheep that are V at codon 126 are susceptible to this type of scrapie, including those that have an R at codon 171.
Generally, the most cost effective way to use genetics to reduce the likelihood of your flock becoming infected is to select rams that carry the RR genotype. All offspring from RR rams will inherit at least one R gene and will be more resistant to scrapie. If RR rams are not available or not practical, a significant reduction in susceptibility can be achieved by using QR rams or a mix of QR and RR rams.
Producer Obligations
The goal of eradicating scrapie is challenging. Producers must meet federal requirements in order to move certain classes of sheep across state lines. States have regulations that apply to the movement of sheep upon change of ownership within the state. Classes of sheep and goats that require official tags to move between states are listed below.
· All breeding sheep regardless of age
· All sheep 18 months or older
· All sheep and goats for exhibition other than castrated males
· All scrapie exposed, suspect, test positive and high-risk animals
· Breeding goats, except low-risk commercial goats
· Sheep under 18 months in slaughter channels that are females which are pregnant or have aborted or sexually intact animals from a scrapie infected flock or herd
In order to receive official identification tags, you need to apply for a Premises or Flock ID number. To obtain this, call toll-free: 1-866-USDA-TAG.
For more information about Scrapie visit: www.sheepusa.org or www.sdsheepgrowers.org
