More Magic from Gene Splicing

A vaccine against foot-and-mouth disease, courtesy of E. coli

Of the many afflictions that plague livestock, none is as devastating as foot-and-mouth disease. Highly contagious and with no known cure, it blisters the feet, tongues and mouths of animals, and causes lameness, weight loss and, in dairy cows, reduced milk production. At least 33 different species are susceptible, mostly such cloven-hoofed creatures as cattle, sheep, pigs, goats and deer. For farmers the usual recourse is to kill, burn and bury infected livestock. Often an entire herd must be slaughtered, even if only one animal has been stricken, lest the disease spread. Some years ago, British authorities had to kill more than 280,000 animals to contain a major outbreak.

In the U.S., foot-and-mouth disease has been stamped out, thanks to the Department of Agriculture's vigilant policies against importing livestock from infected areas. But elsewhere in the world, foot-and-mouth costs farmers tens of thousands of animals and billions of dollars a year. Scientists have developed vaccines against the viral disease, but these carry a risk of actually infecting the inoculated animal because they sometimes contain live viruses.

Now foot-and-mouth may finally be checked. Last week Agriculture Secretary John Block announced that researchers from the California gene-splicing firm Genentech, Inc., in collaboration with his department's scientists, had produced a safe, effective vaccine against the disease. Like polio viruses, the tiny virus that causes foot-and-mouth has a coating of four proteins. A team of Agriculture Department scientists, led by Biochemist Howard Bachrach, had isolated one of them, calling it VP3 (for virus protein). Injecting the substance into test animals, they found it created immunity without causing infection. But using it was risky, because it too involved the danger of introducing live viruses. Moreover, the process yielded only minuscule quantities of the vaccine, hardly enough for commercial production.

In stepped the gene splicers from Genentech, who managed to isolate the gene in the virus that orders up the production of VP3. A molecular fragment containing these instructions was then spliced into a plasmid, or small circular collection of DNA, taken from an E. coli bacterium. Then the plasmid and its "recombined" DNA were inserted back into E. coli. Not only did the recipient bacteria begin cranking out VP3, but all their offspring reproduced the protein as well.

Other gene splicers have accomplished variations of the same feat, but the Genentech-Agriculture Department team says that its production levels are a thousand times as high per bacterium as anything that has been done before. The scientists acknowledge that their vaccine is not a magic bullet against all seven major strains of foot-and-mouth disease.Each has a slightly different protein coat, and each will require a different vaccine. But they are optimistic that the critical proteins can be isolated and then reproduced through gene splicing. If so, in a few years effective new vaccines easily produced in large quantities may finally begin to eradicate this ancient agricultural scourge.

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