Health; Personal Health

The New York Times

By JANE E. BRODY

Published: October 27, 1988

A man who quenched his thirst in a seemingly pristine mountain stream in New England and a woman who did the same while hiking in the Colorado Rockies later developed debilitating diarrhea, abdominal cramps, flatulence, belching and fatigue.

Thousands of others similarly afflicted two years ago had innocently drunk the water from their taps in Missoula, Mont. In 1984 scores of people in northeastern Pennsylvania became ill, and some years earlier hundreds in Essex County, Vt., were felled after drinking municipal water.

The culprit in these and thousands of similar attacks of gastrointestinal disease is a microscopic parasite, Giardia lamblia. In recent years it has emerged as the most common disease-causing protozoan and the most frequent cause of water-borne epidemics in this country.

A generation ago the Giardia parasite was believed to dwell amicably in the human digestive tract, living on remnants of food but never causing untoward symptoms. Then, in 1966, Giardia was identified as the cause of an outbreak of intestinal disease in Aspen, Colo., after the water supply became contaminated with sewage.

But not until the mid-1970's did Giardia start to receive the medical attention it is now known to deserve. For several years hundreds of American and Scandinavian visitors to the Soviet Union had come home with persistent diarrhea and other symptoms that were eventually traced to water contaminated by Giardia that was consumed in Leningrad and other Soviet cities.

Giardia is now recognized to be a worldwide scourge that afflicts 2 to 10 percent of the population in various countries. Studies suggest that as many as 4 percent of Americans may harbor Giardia in the intestines. The parasite can be killed with drugs, but the treatments can be unpleasant. As a result, doctors strongly recommend preventive measures.

Even in developed countries, where community drinking water is cleansed before distribution, Giardia can sometimes escape routine disinfection techniques. The parasite can form tiny capsules, or cysts, that resist destruction by chlorination. Filtration before chlorination is needed to rid water supplies of the cysts. Even well water can become contaminated.

Giardia can also spread easily in day care centers and other institutions, and perhaps even in cafeterias and restaurants. In some day care centers more than half the children have become infected. At least one outbreak among school employees in Minnesota was traced to a shared jar of salmon that became contaminated when a woman opened it after diapering her grandchild.

Many wild mammals harbor Giardia without health complications; water-dwelling animals like beavers are common sources. Hundreds of millions of the parasites can be deposited in a day into the most pristine mountaintop streams and lakes through animal feces. Furthermore, many people carry the parasite but show no symptoms and are capable of transmitting it to others through careless bathroom hygiene. Diagnosis

Control of Giardia is often complicated by difficulties in diagnosis, which may require three or more stool samples before the parasite is found. Because a diagnosis of giardiasis is easily missed and its symptoms can mimic other conditions like gallbladder disease, ulcers or appendicitis, it can result in unnecessary tests and sometimes needless surgery.

In one unusual but illustrative case in Nashville, Tenn., a previously healthy and athletic 57-year-old woman was desperately ill for three months. She spent weeks in the hospital, undergoing dozens of expensive tests, subsisting on a restricted diet and losing weight before giardiasis was diagnosed. Despite several careful inspections of her stool, the parasite had eluded detection, possibly because it typically lives in the upper portion of the small intestine.

People are most often infected by one another, especially in institutional settings like day care centers and homes for the elderly where hygiene may be less than ideal. People, like pets, can be Typhoid Marys, passing along the organism to others but suffering no symptoms themselves.

Diagnosis and Treatment

As common and unmistakable as the giardia parasite is, it is nonetheless often difficult to diagnose. Since the cysts are excreted only from time to time and trophozoites even less often, analyzing just one or two fecal samples may miss them. Parasitologists recommend repeated stool examinations or analysis of a sample of the intestinal contents.

The trophozoites or cysts can sometimes be seen under a microscope, but immunological tests that detect proteins from the parasite are most effective for making an accurate diagnosis.

But veterinarians commonly use a far less accurate test. Veterinary experts say that unless the stool sample is floated in a zinc sulfate solution and then strained and centrifuged, it is very easy to miss the giardia parasite.

Treatment is another problem. There is none known that is 100 percent effective, and all the drugs that kill giardia have nasty side effects. The most commonly used drug is metronidazole (Flagyl), which may cause nausea and vomiting, headache, abdominal cramps, a sharp, metallic taste in the mouth or a secondary yeast infection. Less common but more serious side effects include seizures and numbness and tingling in the arms, legs, hands and feet. Further complicating treatment is that some giardia organisms have developed resistance to Flagyl.

For treatment of a pet and pet owners to have a lasting effect, it is crucial to prevent reinfection. First, if a pet has been given a diagnosis of giardiasis, those in close contact with the animal, and especially any children in the household, might also be tested.

Even a pet under treatment will continue to excrete cysts for a time. If the pet has diarrhea, it may get cysts on its coat and should be bathed. If the pet deposits feces in the yard, they must be picked up as soon as possible. Hands should be washed after scooping the feces or touching the animal and before handling food. Try to keep your pet away from potentially contaminated water sources.

A recently licensed vaccine, GiardiaVax, by Fort Dodge, given annually may help prevent giardia infection in dogs, but there is still no equivalent preventive for people.