The Hunt for Hazards in Drinking Water

Susan McGinley
Sept. 7, 2000

Water teems with millions of organisms most of us will never see, and some we wouldn't want to swallow, either. Good water quality depends on accurate testing and filtering methods to identify and remove pathogens, but sometimes a disease organism is so small that current testing methods don't pick it up. Then the pathogen becomes a floating time bomb, multiplying to a critical mass that will start making people sick.

Often the first to succumb are those with compromised immune systems - people with cancer who are undergoing chemotherapy, or AIDS patients. That was the case with microsporidia (see sidebar). No one had really paid much attention to this group of protozoan parasites until 30-40% of AIDS patients began developing microsporidial infections.

That caught the attention of two scientists in the UA College of Agriculture and Life Sciences, who wondered what was going on.

"One of the things we do is look at emerging pathogens," says Chuck Gerba, an environmental microbiologist in the department of soil, water and environmental sciences. "Here's a thing suddenly showing up in AIDS patients and it's widespread. We start looking at an environmental cause."

Two years ago Gerba and Ian Pepper, director of the University of Arizona Water Quality Center, began working on ways to identify the pathogen because no detection methods had yet been developed. In 1997 Scot Dowd, a UA doctoral candidate, developed a method for detecting microsporidia in the feces of AIDS patients. The other piece of the puzzle left for Pepper and Gerba to solve was how to find the microorganism in the water, an ongoing strategy.

"It's one thing to detect (microsporidia) in a clinical sample and quite another to detect in an environmental sample," Pepper says. The trick was, and still is, to figure out how many microsporidia lurk in large bodies of water. Currently drinking water utilities don't monitor the water supply for microsporidia, and have no means for extracting the organism from the water.

It then became "an organized detective game," as Gerba put it, and he and Pepper began by looking for a pattern. Was it waterborne? Was it alive? How could it be killed through disinfection? And does it survive? These are what water utilities need to know about a pathogen.

In fact, this research is sponsored by the American Waterworks Association Research Foundation, the U.S. Environmental Protection Agency, sanitation districts, and even Amway.

The screening method the researchers devised for waterborne microsporidia combined two DNA isolation methods with an assay method called polymerase chain reaction (PCR) where targeted sequences of DNA are amplified, sequenced and then checked against a known database.

While other methods used for routine screening of pathogens have failed to catch microsporidia, the PCR method "showed the ability to detect less than 10 spores in purified water concentrate samples," according to the researchers. Not only that, the test was able to identify and differentiate different species among the thousands microsporidia that exist that infect both humans and non-humans.

Pepper and Gerba were the first to detect microsporidia in groundwater in Arizona. They have been testing surface water samples from locations throughout the state, and some from California. So far, 50% of the samples tested showed positive for human pathogenic microsporidia. The researchers add that it was detected first in Arizona only because that's where they started testing for it; other states have it, too. More research is needed to determine how widespread human pathogenic microsporidia are in the water supply.