Guardiasis in Paradise

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Giardiasis is not considered to be a killing disease (although it may make you wish you were dead) . . . and some people experience selflimiting infections that disappear after one to several weeks. Then again, many afflicted individuals struggle through prolonged illnesses that continue for months or even years with symptoms waxing and waning. (For example, if you have an unexplained periodic recurrence of diarrhea, you could be the victim of a persistent case of giardiasis.) Even if you've been cleansed of the parasite, you can recontract the disease over and over.

TRANSMISSION

The giardia spreads by waterborne infection and by direct person-to-person (and animal-to-human) contact.

The most common source of infection is drinking water that contains cysts. (Swimming in infected water will also expose you to the parasite.) The organism enters the watershed with the feces from an infected human or animal or by sewage contamination. The cyst is apparently not host-specific and has been found in beavers, muskrats, cattle, sheep, deer, moose, rats, mice, cats, dogs, rabbits, gerbils, and guinea pigs. (Beavers earned their top billing because they were the first identified animal carriers and because their sometimes migratory, aquatic lifestyle made them the Johnny Appleseeds of this disease.) Any infected animal becomes a parasite factory, releasing millions of the cysts into the environment.

It's easy, then, to see why pure tap water can no longer be taken for granted. Indeed, outbreaks of the disease caused by organisms in the municipal water supply have occurred in Rome, New York . . . Banff, Alberta, Canada . . . Camas, Washington . . . Scranton, Pennsylvania ... Leningrad, Russia ... Reno, Nevada . . . and at least half a dozen cities in Colorado.

Such outbreaks are difficult to combat. The cyst is not necessarily killed by the concentrations of chlorine used in municipal water supplies. While proper filtration at the treatment plant is effective, the equipment must be carefully installed, operated, and maintained. (Since present identification procedures are intricate and fallible, it's not always possible to confirm when a water supply has been infected!)

Colorado's solution to the problem has been to require filtration—as well as disinfection—of all public water supplies that rely on surface water. And don't feel smug if you have your own private well. Although the giardia is much less common in underground water supplies, it has been found in wells, cisterns, and—as I learned the hard way—springs.

The persistent protozoan is also transmitted directly by what is known in medical circles as the fecal-oral route . . . being passed from person to person or from pet to person and by food handlers. (Giardiasis can also be transmitted sexually.)

Outbreaks have occurred in orphanages and institutions for the mentally retarded. Recently, a lot of epidemics have been traced to daycare centers, where the infection has been passed from one (often asymptomatic) child to another and then brought home to the diaper-changing parents. Pets, too, play an important role as reservoir hosts, making every gutter and drainage ditch a potential source of infection.

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