MONDAY, May 7 (HealthDay News) -- The meat from hogs and chickens that were fed melamine-tainted surplus pet food poses very little risk to human health, U.S. officials confirmed Monday.

Melamine is the industrial chemical responsible for the massive recall of more than 100 name brands of pet foods in the last two months, following reports of pet illnesses and deaths from liver failure. More than 3 million chickens and 345 hogs have since been identified as having consumed tainted pet food, and much of their meat was sold to the public nationwide, health officials say.

In a prepared statement released Monday, federal health officials said that, using the "most extreme risk assessment scenario," if all the solid food a person ate in one day was contaminated with melamine at the levels found in animals who ate the contaminated feed, the "potential exposure was about 2,500 times lower than the dose considered safe. In other words, it was well below any level of public health concern."

U.S. officials contend 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 used in pet food manufacture. The addition of melamine can falsely inflate the protein content in the foods.

The risk assessment report released Monday was conducted by scientists from the U.S. Food and Drug Administration (FDA), the Centers for Disease Control and Prevention, the Environmental Protection Agency, the U.S. Customs and Border Protection, and the Food Safety and Inspection Service of the U.S. Department of Agriculture (USDA).

The FDA and USDA are in the process of identifying a group of scientists who would be charged with reviewing the risk assessment findings, the statement said.

But on Monday, based on the risk assessment, U.S. officials lifted a quarantine placed Friday on almost 20 million chickens held from the market over concern about their feed, the Associated Press reported. The birds can now be slaughtered and sold to the public.

The FDA has only ever confirmed the deaths of 16 pets from contaminated food since the recall began March 16. But the agency has acknowledged that pet owners have reported the deaths of about 1,950 cats and 2,200 dogs. It's not known how many of those were linked to the recalled pet food.

The findings released Monday that melamine poses very little risk to consumers was echoed by experts interviewed by HealthDay last week.

"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 agreed with recent statements by officials at both the FDA and USDA.

"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.

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

There are many reasons mitigating consumers' risk, the experts said. 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 that 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 original recall of pet foods, by Menu Foods of Ontario, Canada, involved more than 60 million cans and pouches of moist dog and cat food.

More information

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

SOURCES: May 7, 2007, statement, U.S. Food and Drug Administration and U.S. Department of Agriculture; Barry Kellogg, D.V.M., medical director, disaster services, Humane Society of the United States; 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.; May 3, 2007, FDA teleconference with David Acheson, M.D., assistant commissioner for food protection

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