By the end of March, veterinary organizations reported more than 100 pet deaths amongst nearly 500 cases of kidney failure, with one online database self-reporting as many as 3,600 deaths as of 11 April. The U.S. Food and Drug Administration has received reports of several thousand cats and dogs who have died after eating contaminated food, but have only confirmed 14 cases in part because there is no centralized government records database of animal sickness or death in the United States as there are with humans (such as the Centers for Disease Control). As a result, many sources speculate that the actual number of affected pets may never be known and experts are concerned that the actual death toll could potentially reach into the thousands.
Overall, several major companies have recalled more than 5300 pet food products, with most of the recalls coming from Menu Foods. Although there are several theories of the source of the agent causing sickness in affected animals, with extensive government and private testing and forensic research, to date, no definitive cause has been isolated. As of 10 April, the most likely cause, according to the FDA, though not yet proven, is contamination indicated by the presence of melamine in the ingredients of the affected foods. The Chinese company behind the contaminated wheat gluten has initially denied any involvement in the contamination, but is cooperating with Chinese and American investigators.
In the United States, there has been extensive media coverage of the recall. There has been widespread public outrage and calls for government regulation of pet foods, which had previously been self-regulated by pet food manufacturers. The United States Senate held an oversight hearing on the matter by 12 April. The economic impact on the pet food market has been extensive, with Menu Foods alone losing at least $42 million from the recall even without taking into account reduced sales. There have been several waves of recalls, many issued late on Friday evenings possibly to avoid media coverage, and the events have caused distrust in some consumers.
Reports of widespread and possibly intentional adulteration of Chinese animal feed with melamine have raised the issue of melamine contamination in the human food supply both in China and abroad. On 27 April US FDA subjected all vegetable proteins imported from China, intended for human or animal consumption, to detention without physical examination, including: Wheat Gluten, Rice Gluten, Rice Protein, Rice Protein Concentrate, Corn Gluten, Corn Gluten Meal, Corn By-Products, Soy Protein, Soy Gluten, Proteins (includes amino acids and protein hydrosylates), and Mung Bean Protein. In a teleconference with reporters on 1 May, officials from the FDA and U.S. Department of Agriculture said that between 2.5 and 3 million people in the United States had consumed chickens that had consumed feed containing contaminated vegetable protein from China.
Current research has focused on the combination of melamine and cyanuric acid in causing renal failure. Reports that cyanuric acid may be an independently and potentially widely used adulterant in China have heightened concerns for both pet and human health.
As of 7 May, United States food safety officials stated: "There is very low risk to human health from consuming meat from hogs and chickens known to have been fed animal feed supplemented with pet food scraps that contained melamine and melamine-related compounds"
The first recalls were announced by Menu Foods late on Friday, 16 March 2007 for cat and dog food products in the United States. In the ensuing months, many additional recalls were announced by Menu and other companies as the recall expanded throughout North America and to Europe and South Africa. Menu Foods acknowledges receiving the first complaints of sick pets on 20 February 2007 and initiated the recall following unexpected deaths after a regularly-scheduled internal "taste test".
The recalls are related to contaminated vegetable proteins imported from China in 2006 and early 2007 and used as pet food ingredients. The process of identifying and accounting for the source of the contamination and how the contaminant causes sickness is ongoing.
The majority of recalled foods have come from a single company, Menu Foods of Streetsville, Ontario. Menu Foods' recalled products alone represent nearly 100 brands of cat and dog food, and as of 11 April are the only brands known to have caused sickness in animals. Below is an overview of affected brands, as provided by the FDA and the companies:
The American Veterinary Medical Association (AVMA) maintains a combined list of all recalled pet food varieties.
In a potentially related incident in China, on 22 February 2006, Xinhua reported at least 38 cats dying shortly after being fed with Xiduoyu, a brand of a "Tianjin-based cat food manufacturer". A veterinarian referred to in the story said "test results from Beijing Animal Hospital showed the dead cats had suffered from kidney exhaustion and that the sick ones have kidney damage." Suspicions at that time focused on lead poisoning though Gu Junhua, a chief engineer from China's "national feedstuff quality check centre under the Ministry of Agriculture", was reported as saying: "But at present, he said it was difficult to draw any conclusions because the country has not drafted any food safety criteria for pets in terms of the quality and quantity of each element of the ingredients." No mention of melamine was made.
Pet owners were advised to monitor their animals for the following signs of possible kidney failure that may be associated with the unknown toxicant: loss of appetite, lethargy, depression, vomiting, diarrhea, sudden changes in water consumption, and changes in the frequency or amount of urination. It was advised that pets exhibiting these symptoms should be taken for veterinary care as soon as possible, even if the animal did not eat any of the recalled pet food, as these signs may be indicative of other illnesses. Ultrasounds of animals who have eaten the contaminated food in most cases show cortical echogenicity, perirenal fluid and pyelectasia.
One of the largest veterinary hospital chains in the U.S., Banfield clinics, has released statistics on the recent rates of pet kidney failure. Banfield's veterinarians treat an estimated 6 percent of the nation's cats and dogs, and their findings provide "the most authoritative picture of the harm done by the tainted cat and dog food," according to the FDA. Based on analysis of data collected by more than 600 hospitals and clinics in 43 states, out of every 10,000 cats and dogs seen in Banfield clinics, three developed kidney failure during the time pet food contaminated with melamine was on the market. They reported 284 more cases of kidney failure in cats than the expected "background rate," corresponding to a 30 percent increase. During that period the Banfield vets saw 100,000 cats. According to Hugh Lewis, who analyzed the results for Banfield, extrapolating to the United States cat population may mean "several hundred cats a week across the country" were affected. No similar statistically-significant increase was seen among dogs, suggesting that the contamination was more toxic to cats.
The growing number of recalls has motivated at least one well-known animal protection organization, the American Society for the Prevention of Cruelty to Animals (ASPCA) to recommend that "until this crisis is resolved ... pets be fed products containing U. S.-sourced protein supplements only."
Unable to locate the source of the renal failure exhibited by test subjects that consumed some of their wet food products, Menu Foods sent food samples to Cornell University between 13 March and 15 March for chemical analysis. They too, were not immediately able to pinpoint the cause of the sicknesses, so they sent samples to the New York State Food Laboratory, a part of the federally funded Food Emergency Response Network.
On 23 March, the New York State Food Laboratory reported that aminopterin was found in samples sent to them by Cornell. Michigan State University also investigated the source of the renal failure and made available to researchers and veterinarians pictures and photographs of affected animal kidneys "demonstrating acute tubular necrosis in the kidney with intratubular crystals." Aminopterin was widely described in news reports as a "rat poison" though that assertion may be based upon a hypothetical use listed in the 1951 patent application and not upon the actual use of the chemical. Aminopterin is illegal in China and neither Cornell University nor the FDA could replicate the New York lab's results. On 27 March, the American Society for the Prevention of Cruelty to Animals reported that symptoms described in affected animals are not "fully consistent with the ingestion of rat poison containing aminopterin."
In addition to wheat gluten, products containing rice protein have also been contaminated with melamine. Natural Balance Pet Foods recalled two products on 16 April due to kidney damage associated with melamine contamination despite the products not containing wheat gluten. Melamine has also been implicated in corn gluten in South Africa.
Despite the presence of the industrial chemical in both the food and in the animals, the FDA has made it clear that they are still in the middle of an extensive investigation, and "not yet fully certain that melamine is the causative agent."
Prior animal studies have shown that ingestion of melamine may lead to kidney stones, cancer or reproductive damage. One 1945 study suggested the chemical increased urine output when fed to dogs in large amounts. The chemical is known to have a very low toxicity in rodents. The United States Food and Drug Administration (FDA) knows of no studies of melamine involving felines and, if melamine is responsible, the increased sensitivity of cats is a mystery to officials. One hypothesis is that the poisoned cat foods might have higher concentrations of melamine than the dog foods. Melamine can be detected in blood or urine tests.
Stephen Sundlof, director of the FDA's Center for Veterinary Medicine, says "Melamine is not very toxic as a chemical, so we're wondering why we are seeing the kinds of serious conditions, especially the kidney failure, that we're seeing in cats and dogs... We are focusing on the melamine right now because we believe that, even if melamine is not the causative agent, it is somehow associated with the causative agent, so it serves as a marker". Even at the highest observed concentrations found in wheat gluten, the melamine exposure is much smaller than the rat and mouse doses for which effects were seen. Instead, the FDA has suggested that a second contaminant may be responsible for the ill effects and that melamine, as the most easily identifiable contaminant, may serve as a biomarker, or indicator, for contaminated wheat gluten.
According to the FDA, "the association between melamine in the kidneys and urine of cats that died and melamine in the food they consumed is undeniable. Additionally, melamine is an ingredient that should not be in pet food at any level." However, Richard Goldstein of the Cornell University College of Veterinary Medicine has stated that "There appears to be other things in there, other than melamine, but identifying what they are is a long process."
Researchers have focused on the role of melamine and related compounds in causing renal failure. Beginning on 19 April, it was reported that researchers had ruled out aminopterin contamination and had found a "spoke-like crystal" in contaminated wheat gluten and rice protein concentrate and the tissues and urine of affected animals. (It was previously known that melamine and cyanuric acid can form networks of hydrogen bonds, creating a tile-like planar structure through molecular self-assembly.) The crystal has been said to serve as a biomarker for contamination and is approximately 30% melamine. The remainder has been identified as cyanuric acid, ammelide and ammeline, with crystals recovered from urine reported to be approximately 70% cyanuric acid. While some researchers have theorized that the three latter chemicals might have been formed as the animals metabolized the melamine, or as by-products of bacterial metabolism (cyanuric acid is a known intermediate byproduct of bacterial metabolism of melamine), their presence in the crystals found in contaminated protein itself, combined with media reports of widespread adulteration with both melamine and cyanuric acid in China, has focused research efforts on their combined effects in animals. Neither melamine nor cyanuric acid, a chemical commonly used in pool chlorination, have been thought to be particularly toxic by themselves. The current hypothesis is that, although these contaminants are not very toxic individually, their potency appears to be increased when they are present together.
On 27 April researchers from the University of Guelph, in Ontario announced that they had created crystals chemically similar to the ones found in contaminated animals by combining melamine and cyanuric acid in the laboratory under pH conditions similar to that in animal kidneys.
In light of these findings, on 1 May, the American Veterinary Medical Association noted in a press release that the "extremely insoluble" crystals formed in animal kidneys are suspected of blocking kidney function. On 7 May, however, Barbara Powers, president of the American Association of Veterinary Laboratory Diagnosticians and a professor of veterinary diagnostics at Colorado State University cautioned "There's something more going on than just the mechanical blockage. Because you wouldn't see so much necrosis (cell death) and inflammation.”
On 2 May, in further inquiry into the source of the cyanuric acid in the contaminated ingredients and the toxic effects of the chemical combination, Richard Goldstein of the Cornell University College of Veterinary Medicine, in response to reports that the contaminant might be "melamine scrap" left over from processing coal into melamine, hypothesized: “It’s possible the other stuff they were left with was the bottom-of-the-barrel stuff, leftover melamine and possibly cyanuric acid. I think it’s this melamine with other compounds that is toxic.” The composition of the crystals analyzed in contaminated pet food ingredients is similar to the composition of a waste product produced in cyanuric acid production.
On 8 May 2007, The International Herald Tribune reported that three Chinese chemical makers have said that animal feed producers often purchase, or seek to purchase, the chemical, cyanuric acid, from their factories to blend into animal feed to give the false appearance of a higher level of protein, suggesting another potentially dangerous way that melamine and cyanuric acid might combine in protein products.
A toxicology study conducted at the University of California, Davis School of Veterinary Medicine after the recalls concluded that the combination of melamine and cyanuric acid in diet does lead to acute renal failure in cats. Wilson Rumbeiha, an associate professor in MSU’s Diagnostic Center for Population and Animal Health, commenting on results from a survey commissioned by the American Association of Veterinary Laboratory Diagnosticians and designed and implemented by MSU toxicologists which was also presented at the AAVLD's October 2007 meeting, said: "Unfortunately, these [melamine cyanurate] crystals don’t dissolve easily. They go away slowly, if at all, so there is the potential for chronic toxicity.”
American and Chinese authorities investigated the source of the contamination linked to pet deaths, and Chinese authorities closed down Xuzhou Anying Biologic Technology Development Company and Binzhou Futian Biology Technology Co. Ltd., the two compamies linked to the contaminated products.
Many owners of pets stricken after consuming Menu Foods' product have considered filing law suits against the company, but are encountering difficulties with the valuation of the deceased pets. While many pet owners consider their pets to be a "part of the family," lost pets have traditionally been treated as property, with the potential liability limited to the retail value of the animal. Some states define the monetary value of a pet for litigation or insurance purposes. Other states have allowed suits for punitive damages and emotional distress suffered in the loss of a pet.
After word of the recall and reports of animal deaths began to spread, Menu Foods was served with several individual law suits over the deaths of affected pets. On 20 March after the death of her cat, a woman in Chicago, Illinois, sued Menu Foods for negligence in delaying the recall. The same day, lawyers for a Knoxville, Tennessee woman filed suit in Federal Court against Menu Foods for $25 million and hoping to attain class action status, citing negligence in testing the food prior to distribution.
As individual lawsuits were filed across the nation, an Ontario, Oregon family filed a class-action lawsuit against Menu Foods citing emotional damage and economical loss. The lawyers filing the federal law suit noted that Washington state, which has jurisdiction, had a history of favorable consumer protection precedents in prior pet-related lawsuits, but that finding a set value for the lost pets may be difficult..
On 23 March, Menu Foods said that they will reimburse pet owners who can trace their pets' illnesses to the company's products. One estimate is that the cost to owners of treating sickened pets is between $2 million and $20 million.
By 5 April, the 20 March Chicago lawsuit expanded to federal class-action status with over 200 plaintiffs seeking punitive damages for emotional distress. The plaintiffs have specifically accused Menu Foods of fraud, claiming the company may have known of a problem as early as December.
Menu Foods faces 90 class-action lawsuits as a result of the contamination. U.S. District Court Judge Hillman has ordered Menu Foods to have no contact with plaintiffs unless their attorneys are involved in the discussion after lawyers from six firms representing pet owners claimed that the company illegally attempted to contact their clients directly. Hillman has said that "It seems to me that Menu Foods is out to do whatever Menu Foods wants to do in a way that could adversely impact the rights" of the plaintiffs.
A 2004 outbreak involving pet foods sickened more than 6,000 dogs and a lesser number of cats in Asia. Kidney failure in the animals was linked to foods manufactured in Thailand by Mars Inc. Veterinarians in Asia initially blamed the 2004 problems on fungal toxins, but pathology tests conducted in 2007 found melamine and cyanuric acid present in renal tissue from both outbreaks. According to pathologists: "These results indicate that the pet food–associated renal failure outbreaks in 2004 and 2007 share identical clinical, histologic, and toxicologic findings, providing compelling evidence that they share the same causation."