Early this month, Jim Valentine found himself faced with a heart-wrenching decision: the 35-year-old, unemployed computer consultant from Lansing, Mich., had to decide whether to shell out thousands of dollars he didn't have to try to save his beloved dying cat, Silvus. His nine-year-old, silver-furred friend was suffering from kidney failure and he likely needed a pricey kidney transplant. Instead, Silvus was put to death on March 3.

"My only option at that point was to be somewhat financially responsible and have him euthanized," Valentine says sadly, "which was a terrible choice to have to make…. I haven't cried like that since I was 13 years old."

Nearly two weeks later, on March 16, Menu Foods, a Canadian-based pet food manufacturer, announced the recall of over 60 million cans and pouches of wet cat and dog food produced in facilities in Emporia, Kan., and Pennsauken, N.J., between December 3, 2006 and March 6. The massive recall affected 95 different brands—from generic, in-store labels for Food Lion and Wal-Mart to so-called "premium" pet chow like Iams and Science Diet. (Click here for a full recall list) The company has since expanded its recall to all products on store shelves of the types originally withdrawn, in order, it claims, to ensure that all the possibly tainted merchandise is out of the food supply.

The company had received reports of potential problems almost a full month earlier, on February 20. But instead of alerting the public, it initiated "tasting trials" on 40 to 50 dogs and cats. Seven of the study animals died of renal failure, beginning on March 2, five days after the testing started. The company still did nothing, waiting over two weeks longer before finally taking action.

Menu Foods attributes the deaths of 15 cats and one dog nationwide (including the test subjects) to the tainted grub. But others claim the numbers are much higher. The Veterinary Information Network, which boasts a membership of 30,000 veterinarians, reports that at least 471 animals were sickened and 104 died from eating contaminated chow. Sarah Tuite, a spokesperson for Menu Foods, refused to comment on the lag time between the first test animal's death and the date of the recall. As for the discrepancy in death estimates, she acknowledged that "based on the media reports, it probably will increase," but said Menu Foods would have to "look at each case on a case by case basis."

The company believes wheat gluten imported from China is the cause of the trouble, which began about the same time that it switched to a new supplier of the protein (used to thicken the gravy).

The New York State Department of Agriculture & Markets (NYSDAM) determined that two of three samples of food (made with the suspicious wheat gluten) submitted by the company for testing contained a chemical substance known as aminopterin. Aminopterin is a toxin that in the 1940s was the first drug used that produced "durable remissions in children with acute leukemia," says Andre Rosowsky, a professor of adult oncology at the Dana-Farber/Harvard Cancer Center. In the 1960s doctors used aminopterin to induce abortions, but it was banned after a number of failed procedures resulted in severely malformed infants. Rosowsky says aminopterin is no longer in use in the U.S. and Canada except as "an experimental tool" in laboratories.

Aminopterin works by preventing folic acid, part of the B vitamin complex, from aiding in the replication of cells; this compound is necessary for cell division in healthy people but it can be deadly in cancer patients, because it also helps cancer cells reproduce more rapidly. The short-lived cancer therapy has since been replaced in leukemia patients by other drugs such as methotrexate, which is easier to produce, has a longer shelf life and has fewer side effects (it can be toxic to the liver, but damage in many cases can be reversed or reduced if patients stop taking it).

China and some other countries, however, have approved aminopterin for use as a rat poison, according to a report in the Los Angeles Times. The Food and Drug Administration (FDA) reports that the lethal concentration of the chemical is three parts per million (ppm) for rats; the amount found in the contaminated food samples was 40 ppm. There is speculation that the poison got into the chow because Chinese farmers sprayed their crops, including wheat, with it to protect them from hungry rodents.

Stephen Sundlof, director of the FDA's Center for Veterinary Medicine, says, however, that the agency's investigation is not limited to wheat gluten. "It is certainly a likely suspect," he said during a press conference, "but there are other suspects and we will continue to look at all components of the feed." Tuite, the Menu Foods spokesperson, said the company is "still trying to figure out how [aminopterin] got into the food, so I think at this stage, it would be irresponsible of us to identify exactly what ingredient it was on until we know definitively."

Sundlof noted that the FDA has the same authority over pet food as it does over most of the human food supply. "There are really no differences in the regulation of animal food and the regulation of human food," he says. "The same people that inspect human food plants also inspect pet food plants," grading the facilities as high- or low-risk, and then monitoring the high-risk venues more carefully.

"Traditionally, pet food producers are considered to be low-risk because, with few exceptions and this certainly being one of those exceptions, pet food is very safe," Sundlof adds. "We have not had a lot of illnesses in pets as a result of pet food." David Elder, director of the Office of Surveillance and Compliance in the FDA's Center for Veterinary Medicine, said during an earlier press conference that the agency relies more on testing and approving animal foods and drugs before they are put on sale, rather than on routine inspection due to "limited resources."

Details of the recall began to haunt Jim Valentine, who remembered that although he ordinarily fed Silvus dry food, he had splurged on Iams Select Bites in early February. His younger cat, Tiki, wouldn't touch the stuff, but Silvus could not get enough. Valentine alternated the fancy fare with dry food. Three weeks later, he bought a second pouch of the wet food. Then he began noticing some physical changes in Silvus after a few more of the moist meals. Most notably, the cat had developed a swollen bottom lip and had lost a considerable amount of weight. He also stopped eating. Valentine assumed Silvus was avoiding hard food because he was spoiled by the wet treat, so he offered up more of the Select Bites.

About four weeks after first purchasing the soft nuggets, Valentine took the previously healthy and now declining Silvus to the vet. The diagnosis was kidney failure. Silvus—whose weight had plummeted nearly 30 percent from 18 pounds to 13 pounds—had enlarged kidneys. He also had extremely high levels of creatinine (a by-product of the breakdown of phosphocreatine, an energy-storage molecule in muscle) normally eliminated by the kidneys and extremely elevated levels of BUN (blood urea nitrogen), which measures the amount of the waste product urea (a by-product of protein digestion).

The vet administered fluids intravenously, but the blood levels did not improve. Three days later Silvus was dead. Valentine put the rest of his cat's coveted wet food outside for the neighborhood cats to eat. Now, he is worried he may have inadvertently poisoned them, too. "[One of the recalled brands] is exactly the same brand that I had started to feed Silvus," says Valentine, who notes that product numbers on his packages of Iams wet food fell just outside of the range of recalled products. The date codes on his packages were 6256 and 6293; the recall range extends from 6339 to 7073. Nevertheless, Valentine believes that his cat was a victim of food poisoning, raising the question of whether the recall was wide enough.

"The cat is gone; I can't prove it one way or another, but my cat was absolutely healthy at the beginning of February," says Valentine. "There was just nothing wrong with him."

This story echoes that of Mao, Mary Massie's cat of nine and a half years. Massie adopted Mao as a kitten in Ashville, N.C., and the pet followed its now-32-year-old owner on moves to Athens, Ga., San Bernardino, Calif., and finally to Charlotte, N.C., where Massie is working toward earning a fine arts degree in painting at the University of North Carolina at Charlotte.

Massie says that she had fed Mao, a grayish-white cat with bushy fur and a raccoonlike tail, Iams Select Bites for the past two years. On February 24, the cat's energy level was low and he refused food, although he drank water nonstop. Three days later, Massie took Mao to the vet, who diagnosed the cat with kidney failure. The next day, Massie had Mao euthanized.

According to Richard Goldstein, a kidney specialist at Cornell University's Animal Health Diagnostic Center, all of the animals affected by the recall showed similar signs of the poisoning. "There's a specific pathologic phenomenon that we're seeing, which is acute tubular necrosis—acute damage to the tubules to the kidney associated with or in conjunction with these pretty characteristic [round] crystals that we're seeing in the animals' kidneys and urine," he says. He adds that this causes blood creatinine levels to spike anywhere from two to 10 times higher than normal.

Goldstein says that the center received samples of both food products and animal remains from Menu Foods a day or two before the recall. Using liquid chromatography-mass spectrometry (a process that separates complex mixtures and analyzes ingredients by measuring a weight-to-charge ratio), researchers compared the constituent chemicals in the food to standards for common molds, heavy metals and ethylene glycol (or antifreeze, which Goldstein says is the number one cause of kidney failure). All test results were negative.

Cornell's initial tests were inconclusive, so the university sent samples to the NYDASM food safety lab, which has an expanded set of contaminants to compare with the food. This lab detected aminopterin after switching to a UV-light detector to help them visualize the poison; it was initially difficult to pinpoint because of the food's gummy consistency, which makes it hard to load into their machines and then to isolate out components. Goldstein says that Cornell is now trying to replicate NYDASM's results in an attempt to prove definitively that aminopterin is the culprit. "In order to prove it, we'd [also] have to find the compound in the tissue of cats that have died or the urine of cats that have gotten sick," he says.

If we can reconfirm "what was found in Albany," he continues, "[we can] start looking at being able to provide a [screening] test for the pet owners and veterinarians" to determine whether an animal has been poisoned.

Carly Bloom, a veterinarian in Grafton, Mass., says that since the recall, there has been a dramatic jump in the number of worried owners bringing in pets—mostly cats—for blood work, specifically to check their kidney function. Any animals that present symptoms of kidney disease—vomiting, lethargy, anorexia, increased urination and, in some cases, unquenchable thirst—are given 48 hours of intravenous fluids, such as saline solution or lactated ringers, to correct dehydration, supply electrolytes and flush out crystals lodged in the kidney's tubules. "As far as I can see, these cats have been doing pretty well," says Bloom. "I had a case last week that was eating recalled food, came in with elevated kidney enzymes, was on intravenous fluids for two days and then had normal kidney values. I rechecked him a week later, and he is still fine."

Jim Valentine and Mary Massie have both contacted local FDA investigators about their deceased pets, and Massie feels that, at the least, Menu Foods should be required to reimburse her for her vet bills, which totaled nearly $400. "If our product is the cause of pet sickness or death, Menu Foods will take responsibility," says company spokesperson Tuite, who estimates the total cost of the recall to be about $25 million to $35 million in lost revenues. Menu Foods is asking pet owners to keep copies of veterinary records and medical bills as well as receipts for their pet food purchases.

But any monetary compensation would pale in comparison to the price pet owners have paid. "Menu Foods cannot bring Mao back," says Massie. "I'm still a little surprised when I open the door and he's not waiting for me. He's sorely missed."