|Discovery of Nor98-Like Scrapie Found in United States
(January 1, 2008) In February of last year, the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) officially announced the discovery of a Nor98-like scrapie case in a ewe from a flock in Wyoming. This was the first case of scrapie consistent with Nor98 discovered in the United States.
Since then, four more cases have been discovered that originated from flocks in Colorado, Indiana, Minnesota and California. These cases are not related to either the first one in Wyoming or to each other.
This scrapie type was first found in Norway in 1998 and has since been found in sheep and goats in many countries in Europe.
“It does affect goats,” says Diane Sutton, DVM, national scrapie coordinator for USDA. “So far not here in the United States, but chances are, we might eventually see it in goats here too.”
This type of scrapie affects sheep of all commonly occurring genotypes including those that are resistant to classical scrapie.
According to Sutton, those flocks in the United States that are found to be infected with Nor98-like scrapie will not be able to use the current genetic-base approach to flock clean up. Producers whose flocks have risk factors for classical scrapie are still encouraged to test at codon 171 for classical scrapie resistance, as has been done in the past.
The World Organization for Animal Health (OIE) has formed an ad hoc committee to consider how to address Nor98-like scrapie with respect to trade. It will likely be at least two years before a code change could be made should a consensus be reached.
“Until research provides us with other options for eliminating Nor98-like scrapie and the international community reaches a consensus on guidelines for trade we will continue to use flock depopulation and exposure-based clean up plans for Nor98-like scrapie affected flocks,” says Sutton. “As other viable options are identified, we will evaluate them using pilot projects.”
According to Linda Detwiler, DVM, assistant director, Center for Public and Corporate Veterinary Medicine, it is important to note that it isn’t known if the appearance of non-classical scrapie cases in Europe and the United States are more likely due to the increased ability to test for and detect non-classical scrapie than to increasing rates of infection. Scientists in European countries are beginning to look at archived samples in an attempt to identify non-classical cases that may have occurred earlier than 1998.
“I would caution everyone that it’s premature to be able to say much of anything about these non-classical cases. At this point in time, there are many unknowns such as: 1) is there more than one strain, 2) what is the origin, 3) are there natural modes of transmission, 4) does the genotype affect incubation time and clinical presentation, 5) do codons other than 136, 141, 154 and 171 influence these cases and 6) how long have these cases been occurring?” she questions.
Because of Europe’s increased awareness of non-classical scrapie, there has been quite a bit of research into understanding how and if the disease is transmitted and how it affects sheep.
Research is currently underway in the United States.
“The first U.S. material became available in February, so ARS (Agricultural Research Service) is gearing up to study it. But, because of the nature and long-term aspects of the disease, it will take a while to study, so we will probably be seeing research from Europe published first,” Sutton adds.
In the meantime, it is stressed that officials will continue to handle the disease as it has in the past, and that producers should be aware of Nor98-like scrapie but not alarmed.
“We are going to treat it as scrapie until the international community removes it as a trade barrier or science finds that there is a better way to handle it than the current system,” Sutton says.
Jim Logan’s, DVM, chair of ASI’s Animal Health Committee, best advice to producers to protect their flock from Nor98-like scrapie is to maintain a closed ewe flock. He says that to prevent the introduction of all scrapie types, producers need to be aware of where new purchases are coming from, know the genetics of new purchases and avoid purchasing ewes unless familiar with the scrapie status of the farm of origin or maintain a closed ewe flock.
“Essentially, people need to use common sense and maintain good sanitation and husbandry practices,” he explains.