Why Tainted Animal Feed Poses Little Threat to Humans

Differences between species, amounts of melamine consumed are key, experts say

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HealthDay Reporter

FRIDAY, May 4, 2007 (HealthDay News) -- Despite the massive recall of melamine-tainted pet food and numerous reports of dog and cat deaths, consumers really do have little to fear from the news that hogs and chickens sold to the public also ate the tainted feed, health experts say.

So why are pets at risk but not humans?

Because melamine itself carries a very low toxicity to humans, the dose consumers may have received in pork or chicken is very low compared to that eaten by pets in their food, and because cats and dogs also differ greatly -- physiologically speaking -- from their owners.

That's the word from health experts responding to consumer concerns about the widening scare.

U.S. officials charge that companies in China added melamine -- a compound often used to create fire-retardant products -- to exported wheat gluten and rice protein, ingredients that were later mixed into pet foods. The addition of melamine can falsely inflate the protein content in the foods.

The scandal has led to the recall of more than 100 pet food products during the past two months, as well as the quarantine this week of thousands of chickens and hogs.

More than 3 million chickens and 345 hogs suspected of eating feed contaminated with surplus, melamine-tainted pet food have already been sold and consumed by Americans nationwide, health officials say.

However, "nothing that has been shown so far is of real [health] concern, as far as human-consumed products go," said Dr. Barry Kellogg, a Florida-based veterinarian and medical director of disaster services at the Humane Society of the United States.

His view agrees with recent statements by officials at both the U.S. Food and Drug Administration and the U.S. Department of Agriculture.

"We believe the likelihood of a human illness from melamine is unlikely," Dr. David Acheson, the FDA's assistant commissioner for food protection, told reporters late Thursday. He and other government officials say they have so far turned up no sign of melamine-linked sickness in either humans or in the chickens and hogs fed the contaminated pet food.

However, it has been tough for people to square those statements with news that anywhere between 16 and 4,000 dogs and cats may have died from tainted food.

Why might something that may have caused lethal kidney failure in animals be harmless for people eating potentially melamine-tainted meat?

There are many reasons mitigating consumers' risk, experts say. They include:

  • Melamine's low toxicity. "As recently as 2000, [experts] almost took melamine off the list of products to be tested [in foods], because its toxicity is so low," Kellogg said. In fact, one standard measure of a compound's ability to cause harm found that people would have to ingest three times their body weight of melamine to run any serious health risk.
  • Lower dosages. "Remember, dogs and cats are primarily eating just one product, so they were eating [melamine] at high concentrations every day," noted Dr. Stephen Hooser, assistant director at Purdue University's Animal Disease Diagnostic Laboratory. Hooser also suspects that Chinese workers who added the melamine to wheat gluten and rice proteins may have added much more to some lots than to others. "So, there might have been some spots where there was a lot of it, and that got passed on to certain pets," Hooser said. Humans, on the other hand, didn't eat the pet food directly. Instead, it was fed to hogs or chickens who naturally excrete much of the melamine away. In fact, very little of the compound could be expected to settle in the animals' muscle tissue -- the prime source of meat eaten in the United States. And, unlike pets eating a single food, consumers "are not exclusively eating chicken or pork," Hooser said.
  • Different physiologies. "There are lots of differences between species on how they respond to chemicals," Hooser noted. Cats can develop kidney failure from chewing on Easter lilies, and dogs can die after eating grapes -- neither of which harm humans. Cats, especially, have very acidic urine, and it could be that melamine and its metabolite, cyanuric acid (also detected in the recalled pet food), "might form crystals in the kidneys of cats. So, the acidity of their urine may help in the formation of these damaging crystals," Hooser said.

The bottom line: The current melamine scare offers little or no threat to the health of the typical U.S. consumer, the experts said.

The health of their pets is not so certain, however. According to Kellogg, it's still not even clear how many cats and dogs died from eating the tainted products.

"We don't have all the answers yet," the Humane Society expert said. "You have to realize that kidney failure is the number one cause of death and illness in dogs and cats as they age. So, whenever there is media awareness of a problem, everyone is going to look a lot closer."

The FDA has officially put the pet-food linked animal death toll at just 16 dogs and cats. But on Thursday, the agency said pet owners nationwide have reported the deaths of 1,950 cats and 2,200 dogs potentially linked to consumption of the tainted food.

"What's the real number? I honestly, at this point, don't know," Kellogg said.

In the meantime, the recalls roll on. On Thursday, Ontario, Canada-based pet food manufacturer Menu Foods announced it was widening its recall of suspect foods to include cuts of gravy and other select products. An updated list of all recalled Menu Food products is available at the company's Web site at http://www.menufoods.com.

Reacting to the scandal, the U.S. Senate on Wednesday voted 94-0 in favor of stricter production and labeling standards on pet foods, so consumers can be better informed about what they are feeding their pets.

That move came as welcome news to Kellogg.

"I think the pet food industry has been somewhat overlooked in terms of regulation," he said, especially "some of the practices that have gone on and still go on in terms of raising protein content. I always hesitate to look at the 'byproducts' label on food that you buy, because you really don't know what that byproduct might be."

More information

For more information on the pet food recall, visit the U.S. Food and Drug Administration.

SOURCES: Stephen Hooser, D.V.M., Ph.D., associate professor, toxicology, head of toxicology section, and assistant director, Animal Disease Diagnostic Laboratory, Purdue University, West Lafayette, Ind.; Barry Kellogg, D.V.M., medical director, disaster services, Humane Society of the United States, Nokomis, Fla; May 3, 2007, press conference, U.S. Food and Drug Administration

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