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Ethiopian in exile seeks to vanquish cattle plague

The deadly rinderpest disease brought a young Tilahun Yilma to UC Davis in 1965 as an undergraduate student, intent on becoming a veterinarian and returning to Ethiopia to combat the disease.

Friends and colleagues call him “Yilma.” It was his father’s name and means to germinate and grow.

Tilahun, his first name, means to be an umbrella, provide refuge.

Since his birth, it seems, his life has been woven with the warp and weft of ambition and benevolence, fitting for a man who is both scientist and politician, high-achiever and generous benefactor, American and Ethiopian.

And somehow, threaded throughout the tapestry, has been a deadly cattle disease called rinderpest. Virtually unheard of these days in the Western world, it is the source of great suffering and poverty in the fragile developing nations of Africa and Asia.

Yilma, now a professor and microbiologist in the UC Davis School of Veterinary Medicine, first learned of rinderpest from his grandmother who spoke of “Yekebit Elkkit,” the Year of the Annihilation of Cattle. It was in that year, 1888, that Italian troops invading Ethiopia introduced the deadly virus to Africa.

Carried by just three infected cows, rinderpest — meaning cattle plague in German — spread from Ethiopia’s west coast across the Sahel Desert, killing in one year 90 percent of the country’s domesticated cattle, plus countless wild buffalo, giraffe and antelope. An estimated 30 percent 60 percent of Ethiopia’s human population starved to death that year.

Decades later it was rinderpest that brought a young Yilma to UC Davis in 1965 as an undergraduate student, intent on becoming a veterinarian and returning to Ethiopia to combat the disease.

In 1970, with D.V.M. in hand, Yilma joined the international effort to vaccinate Africa’s nomadic herds against rinderpest. For two years, he and colleagues trekked the isolated trails of the nomadic herders along the Ethiopia-Somalia border. The vaccine they administered was effective but impractical for Africa’s rugged conditions. Unstable in the extreme heat, it had to be refrigerated and required syringes, needles and a veterinarian.

More than 125 million cattle were vaccinated during that campaign, and it appeared that rinderpest had been eradicated from Africa. But in 1980 the disease surfaced again in Nigeria, sweeping back across the Sahel all the way to the Red Sea. By then Ethiopia and Somalia were embroiled in warfare, preventing vaccination of livestock to halt the disease.

This time, rinderpest killed an estimated $400 million worth of cattle and caused more than $2 billion in related losses that sapped Africa’s already frail economy. The nomadic herders lost their food supply, and the rinderpest-infected countries were forbidden to sell cattle on the international market.

Despite the failure of the first rinderpest vaccination campaign, Yilma was still intent on conquering the disease when he returned to UC Davis in 1986 as a professor of virology. Intrigued by the potential of the new recombinant DNA technologies, he was convinced that he could develop a rinderpest vaccine for Africa and Asia — one that was simple and inexpensive to produce, easy to administer and would not require refrigeration.

In 1988, after just one year’s work, he announced in the journal Science development of a new genetically engineered vaccine for rinderpest. Although produced through recombinant DNA technology, the vaccine was elegantly simple.

Yilma had identified proteins on the surface of the rinderpest virus that cause an immune response in cattle. He selected the genes that code for two of those proteins, which allow the virus to attach to the cow’s cells and spread from cell to cell. He then plucked those two genes out of the rinderpest virus and nestled them in a weakened form of the vaccinia virus, used earlier to make the smallpox vaccine. This genetically engineered vaccine stimulates the cow’s body to launch an immune response to rinderpest without actually infecting the animal with the disease. If the animal is later exposed to rinderpest, it is already equipped with the antibodies needed to quickly fight off the disease.

Powerful new vaccine

The new vaccine proved amazingly powerful in protecting cattle, even when they were injected with 1,000 times a fatal dose of rinderpest. And it met all of Yilma’s criteria for simplicity and heat stability. Requiring no syringes or needles, the vaccine could easily be scratched onto the neck or abdomen of the animal, producing sufficient immune response to ward off the rinderpest virus. Later, the herder could just peel the scab from an animal’s immunization site, grind it up in a saline solution and, from a single calf, have 250,000 additional doses for future vaccinations.

It took just one year to devise the vaccine and another year to move it through animal trials, but it would take the balance of a decade for the vaccine to clear the political hurdles and gain approval for use in Africa.

“It was the first recombinant vaccine to be released in a foreign country by a U.S.-funded researcher, and there was a lot of fear — political fear,” Yilma recalls.

There also was money to be lost by some northerners, particularly the British, whose colonial past left them with a corner on the tropical medicine industry. Yilma still refers to those who tried to obstruct his rinderpest efforts as “the Mafia.”

With a blend of charm, savvy and bulldog tenacity, Yilma maneuvered his way through the regulatory morass. He needed approval not only from U.S. and African officials, but also from international agencies such as the World Health Organization, the Food and Agricultural Organization and the Office Inernationale des Epizooties, an international organization that deals with animal health issues. Even scientists on the biosafety screening committees were leery of the impact a genetically engineered vaccine might have on the environment.

They were also concerned that herders administering the vaccine might accidentally scratch themselves and get a dose of the vaccine, which carried the live, although weakened, vaccinia virus. For people with weakened immune systems, perhaps caused by the AIDS virus, the vaccinia virus that serves as the basis for the rinderpest vaccine might prove lethal, the critics suggested.

Yilma did not share their fears but nevertheless acquiesced and inactivated two of the genes in the vaccine’s vaccinia virus, weakening it enough to prevent any adverse effects for humans. A recent risk-assessment study of the vaccine indicates that the chance of a person being accidentally inoculated with the vaccinia virus is literally about one in a billion.

Finally, in 1993, Yilma received permission to field-test the vaccine in quarantined facilities in both Kenya and Ethiopia. Results from those trials showed that the rinderpest vaccine provided protection for at least 16 months and probably for life.

“Most scientists would have given up,” says Bennie Osburn, dean of the UC Davis School of Veterinary Medicine. “But Yilma persisted.”

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