Belated Study Clears Cattle
In Wilwaukee Parasite Case

MILWAUKEE — When an outbreak of a waterborne parasite wreaked havoc here a few years ago, government officials were quick to blame cattle. Too quick, it turns out.

It seems livestock have become easy scapegoats whenever a health or environmental problem crops up — note the publicity given to meat-related food poisoning cases and the hush that surrounds vegetable-related cases of identical cause — and that principle was clearly at work in the 1993 cryptosporidiosis epidemic that sickened more than 403,000 people and contributed to the deaths of more than 100.

Only now does a federal report place the blame on human sewage as the source of contamination for Wilwaukee’s city water supply.

A report by the U.S. Centers for Disease Control and Prevention said new studies "suggest a human rather than bovine source," according to the Milwaukee Journal Sentinel.

The CDC study involved DNA typing of cryptosporidium in stool samples from people infected during the waterborne outbreak, plus samples from eight other outbreaks around the country and from cattle throughout the United States.

Two distinct strains of cryptosporidium were found: one type from animals and humans known to have come into contact with animals and another type found only in humans.

The second strain — the kind found in the stool samples from Milwaukee — could not produce infection in animals in lab tests, said Ben Beard, a CDC parasitic disease expert who was the lead researcher.

The finding strongly indicates that human stool in city water drawn from Lake Michigan was the source of the Milwaukee outbreak in March and April 1993, Beard said.

Similar genetic studies from France, Great Britain and other locations where cryptosporidiosis outbreaks have occurred found that different cryptosporidium types are capable of infecting humans and animals, Beard said.

City Health Commissioner Paul Nannis said the research shows there are so many possibilities that the source of the cryptosporidium event may never be known.

Cryptosporidium is a protozoan, an intestinal parasite found in most surface water supplies. It must be filtered out during water treatment.

Changes in treatment methods and problems at a city water plant led to cryptosporidium contamination in Milwaukee's water supply.