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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

June 1996

Battling waterborne bugs

Protect watersheds, and the armies of bacteria and other microscopic creatures will have a harder time advancing on our drinking water supplies.

Robert Manwell

Providing abundant fresh water is one of the most basic services we expect from our municipal governments. More than one half of Wisconsin's five million-plus citizens rely on local governments to collect, process, test and distribute potable water to their homes. An even greater percentage of the public drinks water that has been treated and distributed by a municipal treatment plant at some time during the day at the workplace, in restaurants, at school or in other public buildings.

While chemical contaminants in water pose a risk over time, biological contaminants present the most urgent hazard faced by water utilities. Bacteria, viruses and parasites, increasingly hard to trap and treat, are the cause of nasty flu-like symptoms like diarrhea, nausea, cramps and fever associated with "bad water."

The job of assuring the safety of municipal water supplies is becoming more difficult and expensive. It was the tiny yet potent protozoan Cryptosporidium parvum that sickened 403,000 Milwaukeeans in the spring of 1993. Only four to eight microns in size, so small that 2,500 to 5,000 of them could line up head-to-tail in the space of an inch, the "crypto" bug infested the city's water supply with devastating results. One hundred people eventually died during the crypto epidemic, prompting a full review of how water treatment facilities operate and where cryptosporidium is likely to be found.

Cryptosporidium is not a recent discovery, yet no federal or state standard exists for crypto in drinking water at this time. The same is true for another pesky protozoan with the jaw-breaking name of Giardia lamblia – a similar organism familiar to many outdoors enthusiasts. Both crypto and giardia are common in Wisconsin, the United States and throughout the world.

They're there, but where?

Following the Milwaukee outbreak of cryptosporidosis, the illness caused by cryptosporidium, the Wisconsin Legislature allocated $280,000 to fund a two-year study of crypto. The project was a joint effort between the Department of Natural Resources and the State Laboratory of Hygiene (SLOH). Over 500 water samples were collected from streams, lakes, wells and drinking water treatment plants in the southeast, northeast and northwest regions of Wisconsin. It was and is the largest study of its kind ever done.

Good news and bad news surfaced from the research. On the bad side, every type of drinking water source tested was found to have either cryptosporidium or giardia, or both, present in at least some of the samples collected. Also, crypto was found in about four percent of the finished water samples tested. The good news is that compared to studies from other states, both parasites were found less frequently and in smaller numbers.

Private wells were tested, too. Although generally considered safe because soil and rock above the aquifer filters water, wells that come into contact with rivers or flood water can be contaminated. In the Wisconsin study, crypto was found in one of the six wells tested in Door County, where the aquifer supplying area wells flows in cracked-and-creviced dolomite. This bedrock covered with thin soils easily channels surface water contamination into the groundwater.

The findings didn't surprise researchers. "These organisms have always existed in the environment and will continue to do so," says Joe Ball, a DNR water resource specialist and one of the report's authors. "Our study data suggests that no more than normally expected concentrations exist in Wisconsin's surface waters under average conditions."

Capturing these diminutive pests is not an easy task. Large amounts of water (more than 100 liters) must be pumped through an extremely fine filter. The filter is then scraped and the resulting material examined under a microscope. Because the giardia and crypto organisms are so small and are diluted in so much water, even the best labs isolate and identify giardia or crypto in only about four out of ten test samples. To further complicate things, the test can't tell if the specimens are alive and able to cause an infection, or dead and of no concern.

Nature has provided both of these protozoans with the ability to survive in two very different environments. The infectious form of both crypto and giardia is a hard-shelled capsule called a cyst in the case of giardia, and an oocyst for crypto. These capsules are able to survive in the outdoor environment for up to a year. Some of the highest stream concentrations are found during winter under ice.

Once ingested into the warm, dark gut of a new host, stomach acid dissolves the shell, releasing the organisms which attach themselves to the lining of the small intestine and interfere with the body's ability to absorb nutrients and water. The life cycle is completed when the crypto and giardia reproduce in the gut and form new cysts or oocysts which are passed from the body in the feces.

All creatures great and small carry crypto and giardia

Humans aren't the only creatures favored by this pair of prodigious parasites. Scientists are able to identify several species of cryptosporidium and giardia, and each one seems to prefer a different host. Wildlife is a common source of the giardia found in surface waters, according to Dr. Rebecca Cole, wildlife parasitologist for the National Wildlife Health Center.

"Birds and reptiles generally do not share their form of giardia with humans, but mammals have been found to carry a form that can infect humans," Cole says.

Crypto is common in dairy herds. Common manure spreading practices can wash crypto into streams and lakes. "It's a difficult problem," says Dr. Sheila McGuirk, professor of veterinary medicine at UW-Madison. "There isn't any effective antibiotic for treating dairy herds, and adults can carry the parasite but not have any of the symptoms. Calves pick up the infection from their mothers and show symptoms for a while, especially diarrhea, but eventually their symptoms disappear too." McGuirk says an animal vaccine shows some promise in providing immunity to the herds; if successful, it would reduce the number of oocysts shed by calves.

Although the joint DNR-State Laboratory of Hygiene study was unable to pinpoint a source of the crypto that sickened Milwaukee, unusually high spring runoff conditions in the agricultural lands that are a part of the watershed providing Milwaukee's drinking water are thought to be at least one possible source of the 1993 outbreak.

Fighting what we can't see

Given the abundance and range of crypto and giardia, it's unlikely they will ever be eradicated from the environment. The DNR/SLOH report concludes that the best way to control the spread of these disease-causing organisms is a combination of watershed management and efficient operation of municipal utilities that draw drinking water from the Great Lakes.

Since 1978 the state's Priority Watershed Program has offered grants for the adoption of "best management practices" (BMP) on private lands. BMPs may be as economical as planting grassy strips to slow runoff, as simple as changing the timing of fertilizer application, or as involved as building engineered structures, such as water diversions, sediment basins and manure storage facilities.

Following the 1993 Milwaukee crypto incident the Department of Natural Resources issued new operating guidelines to drinking water treatment plants. By October 1996 municipalities must have a certified operator on duty at all times. Some communities need to install state-of-the-art monitoring instruments and upgrade aging treatment equipment.

Efficient operation of drinking water treatment plants is especially critical during the spring, when melting snow and spring rain is unable to soak into frozen fields, greatly increasing the volume of runoff. Recent studies show that turbid waters carry much higher concentrations of organisms that can tax a treatment plant's abilities to remove enough of the microscopic disease-causing bugs.

Federal and state guidelines designed to eliminate giardia from tap water are not effective against crypto. Scientists are uncertain as to the best practice or combination of practices that will remove cryptosporidium or render it harmless in drinking water. As a start toward developing cost-effective treatments for crypto, the Environmental Protection Agency (EPA) will require drinking water treatment plants to begin sampling and reporting on crypto in their systems. This information will aid EPA in prescribing the most cost-effective treatment for crypto at a future date.

Treatment plant improvements, state-of-the-art treatment technology and watershed managements come with a price, however. Milwaukee is planning a switch from chlorination to ozone treatment – a newer and more effective treatment technology – at a cost of $54.7 million. Additional measures, including replacing filters at each of Milwaukee's treatment plants and extending the Howard Avenue treatment plant intake pipe another 4,000 feet out into Lake Michigan, will bring the total price tag to $87 million.

Actions to maintain the quality of Wisconsin's drinking water supplies haven't been limited to improvements in land management and treatment operations. Researchers aim to set public health standards for cryptosporidium and giardia, but it is difficult to collect and quantify these microbes in water, and researchers have not quantified what doses will cause disease.

Wisconsin Senator Herb Kohl successfully amended to the Safe Drinking Water reauthorization bill to address the problem. It would fund research to investigate new treatment technologies and develop practical methods for detecting microbial contaminants including giardia, cryptosporidium and viruses, and seek reliable and efficient methods to determine when cryptosporidium may cause disease.

Outdoors, don't drink the water

Giardiasis – the illness caused by the giardia organism – is often called "backpacker's disease" or "beaver fever" because campers, paddlers, hunters and anglers are infected after drinking water directly from pristine-looking lakes and streams. All 18 streams tested over the course of the two-year study tested positive at least once for giardia -- even several of Wisconsin's Outstanding Resource Waters, our least polluted streams and lakes. With crypto and giardia so widespread, how can you dodge the infectious cysts while swimming or water skiing or fishing?

It's wise to consider all surface water contaminated no matter how clean and clear it looks, and to resist the temptation to drink without taking adequate precautions first. Take extra care to avoid ingesting surface water around beaches, lakes and streams during periods of heavy precipitation or runoff, when cysts or oocysts are most likely to be present.

State and national parks and forests provide safe drinking water at specified locations in campgrounds, many recreational sites and buildings. In the interests of health, these water supplies are subject to the same testing requirements as other public water supplies. But backcountry travel is another matter. Preparedness and caution offer the only line of defense against waterborne disease.

There are three basic strategies for water treatment in the outdoors.

  • Boiling is tried and true but takes time and fuel, and leaves the water tasting flat. Also, while one minute at a rolling boil is recommended at sea level, boiling times increase to three to four minutes at high altitudes.
  • Chemicals (iodine tablets or crystals are most common) take from 20 minutes to an hour to work properly, depending on water temperature, clarity and acidity. It's difficult to judge these factors, so the safe route is to wait the maximum amount of time, every time. Iodine leaves a distinctly medicinal taste and can be harmful to fetuses and people with thyroid problems.
  • Small water filters, ranging in price from $40 to $250 are convenient, fast and reliable. Most can process about a quart of water per minute and can filter anywhere from 100 to 5,000 gallons of safe drinking water before the filter must be replaced. Some have prefilters to strain out the algae and larger suspended particles before the water reaches the really fine-pore filter. Most have replaceable filters and some permit cleaning of the filter.

No "cure" for crypto

Cryptosporidium is not a new organism, but it is newly understood as a health threat. In otherwise healthy individuals cryptosporidosis is a self-limiting illness, meaning that the body's immune system will eventually defeat the infection. While there is no effective medical treatment available for crypto, there is evidence that healthy people develop an immunity to crypto after an initial exposure. McGuirk notes that people from farming backgrounds seem to be less susceptible to repeat infections compared to urban dwellers.

But for those with weakened immune systems, crypto can be deadly. Organ transplant recipients, people with AIDS, and people undergoing chemotherapy are especially vulnerable to cryptosporidosis. Others facing increased risks of infection are child care workers and anyone that comes in contact with feces at home, on the job or the farm.

The situation is somewhat brighter for giardia. From 1990-1994, Wisconsin averaged 1,614 giardia cases per year, but giardiasis is treatable with several easily available drugs once an accurate diagnosis is made. Making that diagnosis usually involves several trips to the doctor's office with stool samples since the telltale cysts are not always present in every stool.

Protecting our water by protecting our watersheds

The Natural Resources Defense Council says there were at least 116 outbreaks of disease borne by drinking water in the United States between 1986 and 1994. The group also reports that more than 25,000 water systems serving 92 million Americans were out of compliance with Safe Drinking Water standards in 1993-94.

Statistics like these should be a call to action. Although a water utility's jurisdiction generally ends at municipal borders, it can participate in total water quality management by maintaining contact with regional planning commissions, the DNR and upstream industries and municipalities. Under DNR's new structure, basin management teams – DNR resource managers and representatives from agriculture, industry and municipalities within a water basin – will plan and allocate resources for watershed management.

Protecting our watersheds as much as possible from human and animal wastes provides an important firewall between humans and cryptosporidium and giardia. At the same time, we must realize that both organisms are prevalent in the environment and may also be found in high-quality filtered water. For municipalities, installing more effective treatment alternatives, such as ozone treatment, and operating treatment systems at peak efficiency at all times, can backstop watershed management practices.

Not only in water

Drinking water supplies represent the greatest potential for large-scale outbreaks of crypto and giardia, but there are other ways these parasites can be passed. Giardiasis is a common ailment of children in day care centers. Statistics from the Department of Health show that children under the age of five are three times more likely to contract giardiasis than older children or adults. With a large concentration of diaper-age children present, child care providers must maintain strict hygiene regimens to break the oral-fecal infection cycle. Although scientists are not sure how many giardia cysts it takes to infect a human, it is known that a soiled diaper can contain millions.

Robert Manwell writes from Madison, Wis.