International concern over diseases such as BSE is pressuring scientists to develop better diagnostic tools.
“Everybody is hoping for a breakthrough,” says Shane Renwick, director of the Canadian Food Inspection Agency’s animal health laboratory service.
“It is something that would be extremely valuable, helping the industry worldwide and helping us put a lid on this disease once and for all.”
While many countries are searching for a reliable live diagnosis, one of the world’s leading test manufacturers says it is not going to release a new test until it is absolutely sure it works.
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“Our strategy is to go to the market with cutting edge technology, not with ‘me too’ products,” said Markus Moser, chief executive officer of Prionics AG, a biotechnology company working on diseases that are transmitted between species.
Besides its BSE work, Prionics is looking at tests for brucellosis and Johnes disease in cattle and trichinosis in pigs.
There are at least 11 European Union approved rapid tests and Prionics recently introduced a new rapid test strip kit that the CFIA has evaluated and plans to acquire. It was approved for use in Europe last February.
Called the Prionstrip, Moser said it is a response to North American requests for faster tests.
The test is a credit card shaped kit with a special formula on small, white strips attached to the card. Liquefied brain material is placed on the strip and if it develops a blue line, the sample is positive for BSE. It responds within 100 minutes and is useful for high-throughput laboratories. The results can be read electronically rather than manually and it takes between one and two minutes per test.
“In the end it boils down to cost and the highest costs are with the laboratory personnel,” Moser said from his office in Schlieren, Switzerland.
Prionics Check Western is another commonly used rapid test. Signals generated by the test provide a protein specific molecular fingerprint using antibodies to attach to the infection. It is commonly used for mass screenings and as of the end of 2004 it had been used more than 20 million times.
Canada, Europe and Japan also use a Bio-Rad Laboratories kit based on the ELISA technique, or enzyme-linked immunosorbent assay. It is a rapid immunochemical test that uses an enzyme to create a biochemical reaction. The test purifies brain tissue and samples placed on a microplate are processed to detect abnormal prion protein, usually with a colour change.
When rapid tests show a potential positive result, the screenings are sent to a national reference laboratory for further examination, which could take up to two weeks using the gold standard immunohistochemistry test.
The technology uses a cocktail of antibodies called polychonal antibodies that attach themselves to prion proteins.
Earlier in June, the United States agreed to retest samples from a cow ruled negative last November. Moser said the U.S. problems arose when it used monoclonal antibodies rather than the broader spectrum technique.
If a test relies on only one antibody, an anomaly might appear in the sample that indicates something is wrong but isn’t necessarily BSE. However, if many antibodies are used, there is no problem distinguishing between the real signal and the anomaly.
Canada switched to a polyclonal antibody system several years ago.
