Friday, May 27, 2011

Rinderpest Has Been Eradicated

Rinderpest, which means "cattle plague" in German, is highly contagious and has a fatality rate of about 80 percent. It is the only animal disease to have been eradicated; smallpox occurs only in human beings.

Rinderpest, a cattle disease that for centuries felled herds in Europe, Africa and Asia and caused periodic human famine, has been eradicated, veterinary epidemiologists announced this week.

Eradication is the Holy Grail of disease prevention and has been successful only once before. Smallpox, an equally devastating human scourge, was eradicated in 1980, proving it is possible to stamp out a microbe across the entire planet. Attempts are underway to rid the world of polio and Guinea worm disease.

The bovine equivalent of measles, rinderpest is described in ancient Chinese writings and in documents from the Roman Empire. It hobbled Charlemagne when he moved herds to support his armies in the 8th century. When it entered Ethi­o­pia in 1889, it caused starvation that killed one-third of the country’s human population, even though the microbe does not infect people.

William R. White, a rinderpest expert at the U.S. Department of Agriculture, said: “The suffering that this disease has caused through the millennia is incredible. This is probably the greatest achievement in veterinary medicine.”

Three things made rinderpest eradicable. Animals that survived infection became immune for life. A vaccine developed in the 1960s by Walter Plowright, an English scientist who died last year at 86, provided equally good immunity. And even though the virus could infect wild animals, it did not have a reservoir of host animals capable of carrying it for prolonged periods without becoming ill.

Rinderpest appears to have emerged in Asia. In Europe it was sometimes called “steppe murrain,” or cattle disease from the steppes. It was never endemic in the Americas. An importation to Brazil in 1921 was contained, as was one to Australia a few years later.

The most recent recorded outbreak occurred in Kenya in 2001. Much of the past decade has been spent looking for new cases, in domesticated animals and in the wild, wandering herds of ungulates, or hoofed animals, in East Africa. The last place of especially intense surveillance was Somalia, where the final outbreak of smallpox occurred in 1977.

In 1994, the FAO launched an eradication program that was largely financed by European countries, although the United States, which never had rinderpest, also contributed money. The effort consisted of massive vaccination campaigns, which were made more practicable when two American researchers made a version of the Plowright vaccine that required no refrigeration.

The vaccine consists of an extremely weakened form of the rinderpest virus. While it has never been known to cause disease, its use has been stopped to prevent the chance that it might “revert to pathogenicity” and cause the disease it is trying to prevent.

Ridding the world of other infectious diseases, however, has proved even more difficult.

Smallpox eradication took 11 years of intensive effort and was aided by a hard-to-miss rash that made finding cases easy. The effort to eradicate polio, launched in 1988, has proved far more arduous. It is now 11 years past its original deadline, with the virus — which in most cases causes no obvious symptoms — still circulating in eight countries. An effort to eradicate malaria failed spectacularly in the 1950s.

Guinea worm disease, a waterborne disease caused by a parasite, is the next likely eradication success. Last year about 1,800 cases were recorded in four African countries, down from 3.5 million cases worldwide in 1986.

No comments: