Water Filters and Giardia

Kyoto: Hiking from Kibune to Kurama

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Transmission and Control - Introduction

During the past fifteen years giardiasis has been recognized as one of themost frequently occurring waterborne diseases in the United States (1).Giardia lamblia have been discovered in the United States in places as farapart as Estes Park, Colorado (near the Continental Divide); Missoula,Montana; Wilkes-Barre, Scranton, and Hazleton, Pennsylvania; andPittsfield and Lawrence, Massachusetts just to name a few. In light ofrecent large outbreaks of waterborne giardiasis, it seem timely to presentreliable information on the way in which giardiasis is acquired, treated,and prevented.

Prevalence and Symptoms

Giardiasis is a disease caused by a one-celled parasite with thescientific name Giardia lamblia. The disease is characterized byintestinal symptoms that usually last one week or more and may beaccompanied by one or more of the following: diarrhea, abdominal cramps,bloating, flatulence, fatigue, and weight loss. Althoughvomiting and fever are listed as relatively frequent symptoms,they have been uncommonly reported by people involved in waterborneoutbreaks of giardiasis in the United States. Giardia, however, rarely causes intestinal bleeding. Therefore, blood in the stool of a patient with giardiasis almost always indicates the presence of a second disease.

While most Giardia infections persist only for one or two months, somepeople undergo a more chronic phase, which can follow the acute phase ormay become manifest without an antecedent acute illness. The chronic phaseis characterized by loose stools, and increased abdominal gassiness withcramping, flatulence and burping. Fever is not common, but malaise,fatigue, and depression may ensue (2). For a small number of people, thepersistence of infection is associated with the development of markedmalabsorption and weight loss (3). Similarly, lactose (milk) intolerancecan be a problem for some people. This can develop coincidentally with theinfection or be aggravated by it, causing an increase in intestinalsymptoms after ingestion of milk products.

Some people may have several of these symptoms without evidence ofdiarrhea or have only sporadic episodes of diarrhea every 3 or 4 days.Still others may not have any symptoms at all. Therefore, the problem maynot be whether you are infected with the parasite or not, but howharmoniously you both can live together, or how to get rid of the parasite(either spontaneously or by treatment) when the harmony does not exist oris lost.

Medical Treatment

Three drugs are available in the United States to treat giardiasis:quinacrine (Atabrine*), metronidazole (Flagyl*), and furazolidone(Furoxone*). All are prescription drugs. In a recent review of drug trialsin which the efficacies of these drugs were co mpared, quinacrine produceda cure in 93% of 129 patients, metronidazole cured 92% of 219, andfurazolidone cured 84% of 150 patients (4). Quinacrine is generally theleast expensive of the anti-Giardia medications but it often causesvomiting in children younger than 5 years old. Although the treatment of giardiasis is not anFDA-approved indication for metronidazole, the drug is commonly used forthis purpose. Furazolidone is the least effective of the three drugs, butis the only anti-Giardia medicatio n that comes as a liquid preparation,which makes it easier to deliver the exact dose to small children andmakes it the most convenient dosage form for children who have difficultytaking pills. Cases of chronic giardiasis refractory to repeated coursesof therapy have been noted, one of which responded to combined quinacrineand metronidazole treatment (5).

(*) Use of trade names is for purposes of identification only.