29 March 1996

Fingerprint

of an agent…

Fears of a link between BSEand CJDrefuse to disappear. FARMERS WEEKLYs livestock team details the latest scientific evidence that shows there is no cause for panic

NO ONE knows for certain what the BSE infective agent is or looks like. But scientists at the Institute for Animal Healths Compton Laboratory in Berkshire have devised a method of fingerprinting it (and other agents responsible for transmissible spongiform encephalopathies in other species).

According to institute director Prof John Bourne, work to date has shown that in all cases of BSE examined there the agent had the same fingerprint, unlike scrapie for which a number of different fingerprints have been recognised, but none of them is like the BSE one.

Currently the institute is also working on fingerprinting material from Creutzfeldt-Jakob disease cases before and after BSE was first identified. In six months time fingerprinting of material from the recently discovered "new" strain of CJD will begin.

The work involves infecting special strains of mice with the materials and measuring the incubation period and examining the brains for the site and nature of any damage resulting.

Prof Bourne says the typing method has proved to be very precise, but with incubation periods of 400 days or more the work cannot be hurried and results from the latest CJD strain are probably 18 months away.

There are two theories about the exact nature of the infective agents in these diseases, he says. Either it is the prion protein itself or it carries an agent.

"Our view is inclined towards the idea that the prion protein carries the agent."

Compton is also working to develop live tests for these diseases. ButProf Bourne admits such test are still a long way off.

Initial attempts to test for BSE infection in live animals have been disappointing as the pathogen cannot be detected in peripheral tissues and fluids.

Dr Chris Bostock of Compton Animal Health Institute, Berks, said that in cattle the disease itself did not affect peripheral fluids and tissues.

"As BSE develops within the animal, proteins that occur normally take on a different form. This is called a prion," he says.

Detecting these prions in the early stages of infection in live animals has to date proved impossible and work is continuing to make the test more sensitive.

&#8226 One man who claims to have developed a live test for BSE says that a type of virus is responsible for the disease.

Dr Harash Narang says that the pathogen could be found in urine with a simple test.

When working at Newcastle University, he claimed that the pathogen comprised a prion central core, wrapped in single strand DNA and coated in a normal protein.

"This is why the virus is not detected by most tests and has to date eluded efforts to isolate it," says Dr Harang.

Prof John Bourne – fingerprinting material from CJDcases before and after BSEfirst identified.