When a pediatrician at a Hong Kong hospital needed to learn more about the effects of ingesting the industrial chemical melamine, he reached outside human medicine to ask Ken Thorley.

A University of Melbourne-trained veterinarian with expertise in emergency medicine, Dr. Thorley, now practicing in Hong Kong, went down a similar path less than two years ago, when roughly a dozen of his patients suffered acute renal failure. What followed were news reports showing pet food laced with melamine caused renal disease and death in thousands of dogs and cats around the world. It took a massive recall of more than 150 brands of pet food to stem the tide of illness.

Now, 18 months after U.S. authorities learned about the pet food problem, businesses once again are suspected of adding melamine, a nitrogen-rich chemical used in fertilizer and plastics manufacturing, to boost the apparent protein content of food products. This time, tainted milk is blamed for killing at least three babies in China and sickening 54,000. The contaminated milk, first discovered in formula, has since been found in chocolate and other candy, instant coffee and milk tea.

The latest episode has Thorley, of the Victoria 24-Hour Veterinary Hospital & Clinics, again puzzling over images of kidneys.

“Unlike in humans, kidney stones have not been part of the pathology in cats or dogs — only crystals at the microscopic level,” Thorley said in an interview by e-mail. “I am wondering if the tendency for melamine to form potentially removable stones rather than more widely dispersed tubular damage may result in lower mortality in humans. I have not able to find any information about this because the human condition is still unfolding...”

He also wonders whether the melamine nightmare hasn't ended for his four-legged patients.

"In the last 12 months, we have been getting a lot of young cats with unexplained renal failure," Thorley said. "One renal biopsy result came back that the kidneys had been damaged by 'unusual' crystal deposition causing renal failure. The histopathologist wasn't sure what the crystals were. He thought they might have been ethylene glycol (antifreeze), which is surely impossible in subtropical Hong Kong.

"Cats and dogs drink milk and consume milk products," Thorley noted. "To say anything more than that is only conjecture at this time."

Pet food industry leaders in the United States say the recurrence of melamine contamination in food products from China should have little to no impact on pets here this time around. "The pet food industry doesn't use much milk," said Rick Shields, executive vice president of technical services at Menu Foods Inc., a leading pet-food maker hit hard by last year's recall.

Kurt Gallagher, director of communications and export development at the Pet Food Institute, said that in the aftermath of the recall, the industry came up with a test to check for melamine. "Now that such a test has been developed, it is possible to defend against melamine in protein products," he said.

All the same, a melamine hangover lingers over parts of the $15.8 billion industry.

On Tuesday, a U.S. District Court in New Jersey is expected to finalize a $24-million settlement of 100 class action suits that sprang from the recall in the United States and Canada. If approved, the settlement would pay eligible pet owners 100 percent of their documented economic damages, or up to $900 of undocumented damages.

Meanwhile, although retail sales of dog and cat foods are growing overall in the United States, figures by Euromonitor International show that sales of wet dog food rose only .52 percent in 2007 over the previous year, compared with 5.54 percent for dry dog food. The difference in cat food was even greater: Sales dipped 1.41 percent for wet cat food in 2007 while dry cat food gained 6.73 percent.

Wet food — in particular, meat chunks in gravy — was at the center of the recall. The melamine was mixed with wheat gluten, which helps form the chunky shapes.

For 2008, Euromonitor projects a continued slide in sales of wet dog and cat food, predicting drops of .26 percent and 1.55 percent, respectively, according to figures supplied by the Pet Food Institute.

The impact was severe at Menu Foods, a Canadian-owned manufacturer contracted by numerous companies to produce their private-label or name-brand wet pet food. Before the recall, Menu had four plants and about 1,000 employees. Following the melamine scandal, Menu was down to three plants in Kansas, New Jersey and Ontario and a workforce two-thirds its original size.

The downsizing wasn't caused entirely by the contamination. About the same time, one of Menu's customers was acquired by another company whose policy was to make their own food, said Shields, Menu's executive vice president of technical services.

But one direct consequence of the recall was that Menu lost its biggest client, Iams. A spokesman for Iams, which is owned by Procter & Gamble, declined to comment. Shields attributed Iams' decision to an attempt to distance its brand from an unlucky associate.

"We were pretty much the hub of the wheel of attention," Shields said.

Menu's mistake was acquiring wheat gluten from ChemNutra Inc. of Las Vegas. ChemNutra received the tainted imports from China and sold the product to pet-food manufacturers. The company and its owners, along with two Chinese companies and their top executives, were indicted by a federal grand jury earlier this year for their roles in the scandal.

Shields said Menu Foods had purchased wheat gluten from ChemNutra for only a few months before the contamination was discovered. "Any of our customers know that what happened to us could have happened to anyone,” he said.

As a result of the melamine disaster, Shields said, Menu Foods has cut its business with China to a minimum. "We're down to a few chemicals like vitamins that there's nowhere else but China to buy from," he said.

He acknowledged that the company may be spending more for ingredients as a result, but how much more, he doesn't know. "No one's given them a phone call to find out what the price is because we don't care," Shields said.

The decision of companies such as Menu Foods to dissociate from China has been a boon for domestic suppliers such as MGP Ingredients, Inc. Located in Kansas, MGP began producing wheat gluten in the 1950s. Times got tough in the 1990s due to competition first from the European Union and Australia, then China.

"These imports oftentimes were sold in the U.S. market at prices below U.S. production costs, making it impossible for U.S. manufacturers to compete on an even basis," Steve Pickman, vice president of corporate relations, said in an interview by e-mail.

"Since the melamine scare, we have experienced increased demand for wheat gluten produced in the U.S.," he reported. "This demand has held fairly steady since the issue arose and, as a result, our production levels have increased."

The level today is double to triple that before the melamine mess, though it is still below its historic peak, Pickman said.