Melamine is a non-protein nitrogen source with a variety of uses, including fertilizer. It is believed that melamine has the potential to cause kidney damage because of crystal formation in kidney tubules, tiny tubes in the kidneys that act in parallel to filter blood and produce urine. When the crystals form, it is thought that they damage the lining in the tubules, which can lead to kidney failure.

Signs of kidney failure, as evidenced by the dogs and cats that were affected by pet food contamination, include initial increases in the frequency of urination, becoming less and less frequent as the kidneys fail.

Signs of kidney failure have occurred soon (usually a matter of days) after the consumption of contaminated products.

The threat to humans who consume meat products from contaminated animals is still under review. Scientists are studying whether melamine also penetrates muscle, and to what effect (both for the animal, and those who consume it).

Since few in the United States consume swine kidneys directly, it is thought that the risk to human health from the possible hog contamination is relatively small.

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Source: Jeffrey O. Hall, head of Utah State University's Diagnostic Toxicology Laboratory