Domestic Animal Disturbances

CHURCHVILLE, VA—Mad cow disease has now reached Canada—one case, affecting a beef steer in remote Alberta. No one knows how the disease got there. Across the Atlantic, in Britain, more than 167,000 cows have been diagnosed with the disorder since 1986.

Fortunately, fewer than 150 people have died from “new variant Creutzfeldt-Jacob disease” (nvCJD), the fatal human disease linked to “mad cow,” and the rate of new cases has slowed to a near-halt.

Awful as are 200 hopeless, lingering human deaths, the toll has been much less than we had feared it would be. At one time, authorities believed that Europe’s “mad cow” epidemic might eventually claim 800,000 human victims. First World countries have long since banned the feeding of potentially infectious animal nerve and brain tissue to ruminant animals, the apparent source of the mad-cow epidemic.

The human death toll from the world’s current SARS (Severe Acute Respiratory Syndrome), outbreak is above 250 and climbing. As it turns out, SARS, too, is an animal-transmitted disease. The most likely source is the wild civet cat, which is still hunted and eaten in China. Virus samples from civet cats are genetically very similar to the coronavirus that causes human SARS, and China’s wild game vendors have an elevated count of SARS antibodies.

In addition, at least ten Americans have been hospitalized for treatment of monkey pox, a viral infection. The outbreak has been traced to pet prairie dogs sold from a pet shop, where they may have come in contact with a Gambian pouched rat from Africa. (The United States has banned the sale of prairie dogs, pouched rats, and five other rodent species.)

Sad as these developments are, they should not surprise us. As long as human beings have been keeping domesticated animals, the latter have given diseases to humans. For many years we have lived with various semi-deadly strains of Asian flu viruses, which are widespread among that densely populated region’s poultry flocks. Recently, Hong Kong officials ordered the slaughter of all of the colony’s poultry in 1997 after six people died of “Avian flu.” Studies showed that the virus spread readily from chickens to people but was much less contagious from one person to another.

Some researchers think that the AIDs virus entered the human population through the consumption of monkey brains as a delicacy. History’s worst human disease pandemics occurred, of course, when Europeans brought to the New World all the diseases they had contracted—and developed resistance to—from their interaction with domestic livestock. Dr. Jared Diamond, author of Guns, Germs and Steel, says that we contracted measles, tuberculosis, and smallpox from cattle; influenza from pigs and poultry; and yellow fever from African monkeys.

The American Indians had no domestic livestock except dogs—and no resistance to the European diseases. The Spaniards’ inadvertently brought smallpox with them, which devastated the Aztec and Inca societies in Mexico and Peru, along with the big mound-building societies in North America’s Mississippi Valley. Scourges of measles, typhus, diphtheria, mumps, tuberculosis, and yellow fever followed soon after.

Diamond estimates that the New World had about 20 million inhabitants when the Europeans landed. Ninety percent of that number probably died within the first century of the Europeans’ arrival, the vast majority as victims of the European animal-derived diseases.

Fortunately, it is extremely unlike that there will be even a single human death from Canada’s one current “mad cow” case. The rate of transmission from cattle to humans cannot possibly be high. The eventual human death toll from nvCJD may be well under 200, whereas Britain must have had nearly 200,000 “mad cows,” thousands of which went into the food chain before 1986.

There was no way to predict or prevent the initial wave of mad cow disease. Prions, “proteins gone mad” which scientists didn’t even know could be infectious, are now thought to have jumped from sheep to cattle and then to humans. It appears that this process was inadvertently aided by changes in British rendering requirements in the early 1980s—adjustments that were designed to cut energy use and reduce workers’ risks of impairment by strong chemicals. Even the precautionary principle—the idea that humans should not adopt technological changes that involve nearly any possible health risks—quails in the face of such long odds.

While remaining on the lookout for diseases spread by human-animal interactions, we must remember that humanity might never have achieved the affluence so many societies enjoy today had we not begun to domesticate animals. They provide high-quality protein and key micronutrients through meat, milk, and eggs. They grew the wool for our winter clothing during the Ice Ages, and they pulled our plows and carts. They guarded our homes and granaries. Companion animals (cats, dogs, horses, parakeets, etc.) enrich us emotionally.

Humans will continue to raise domestic livestock; hunt and eat wild animals; and keep companion animals in increasing numbers. We can minimize the spread of disease by making sure to fund enough medical research and regulatory knowledge to deal with the inevitable side effects of this complex and beneficial relationship.