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Most persons with symptomatic giardiasis have an illness which is uncomfortable and requires treatment but is usually not severe or life-threatening. It is now recognized, however, that some persons do have severe diarrhea with significant volume depletion, which necessitates hospitalization (Lengerich et al., 1994; Robertson,
1996). In some of these severe cases, a hypokalemic myopathy has been described (Cervello et al., 1993). In a US study, rates of hospitalization for Giardia were similar to those for Shigella (approximately two cases per 100000 persons and about 4600 annual admissions) and highest for children under the age of 5 and for women of child-bearing age (Lengerich et al., 1994).
Chronic Giardiasis and Nutritional Abnormalities
Chronic giardiasis is characterized by malaise, fatigue, diffuse abdominal cramping and stools which are usually greasy and foul-smelling. Weight loss is nearly always present in these cases. Over time there may be periods of constipation with clinical improvement, but it is typical for the diarrhea to return.
In chronic disease there may be evidence for malabsorption of fat, vitamins A and B12, protein, D-xylose, iron and lactose (Solomons, 1982; Jove et al., 1983; Welsh et al., 1984; Gillon, 1985; Sutton and Kamath, 1985). Of the dis-accharidases, deficiency of lactase is most common, and may persist for several weeks
after therapy. All patients should be instructed to avoid lactose-containing products during this recovery period, so that any recurrent diarrhea will not be confused with relapse of infection.
Failure to thrive in children is associated with Giardia (Burke, 1975; Hjelt et al., 1992; Lengerich et al., 1994). It is not known, however, how many infected children will develop this syndrome, neither it is known which parasite or host factors influence the outcome, since the pediatric age group is also the most likely to have asymptomatic excretion of parasites. Also, while failure to thrive has been attributed to giardiasis in children in the developed world, the role that Giardia plays in chronic diarrhea and malnutrition in developing regions is less defined. In settings of poor hygiene, infection with Giardia during childhood is nearly universal (Islam et al., 1983; Gilman et al., 1985; Mahmud et al., 1995) but it is often one of many pathogens to infect children (Kaminsky, 1991; Lanata et al., 1992; Meloni et al., 1993). Therefore, it is difficult to attribute diarrheal symptoms to Giardia alone. Nevertheless, for some children Giardia appears to be the most important cause of diarrhea and malnutrition (Mata, 1978; Islam et al., 1983; Farthing et al., 1986; Kaminsky, 1991; Sullivan et al., 1991a).
In summary, Giardia can produce chronic diarrhea, failure to thrive, and severe illness requiring hospitalization. It also may cause asymptomatic infection or be one of many infecting pathogens, when it could act synergistically to cause diarrhea and malabsorption. The variety in outcome is likely related to the infecting strain of Giardia, the underlying nutritional status of the host, and the host’s previous experience with the parasite. Until isolates of Giardia from these various settings can be analyzed for their pathogenic potential, the resolution of this debate is not likely.
The initial consideration of giardiasis is based on clinical findings—a patient with diarrhea that is prolonged and associated with weight loss, but who usually does not have fever, significant vomiting, tenesmus or blood in the stool.
Frequently there are important epidemiologic factors of travel, camping or exposure to conditions of poor fecal-oral hygiene. However, the ubiquitous nature of the parasite should place it in the differential of most cases of noninflammatory diarrhea. As an example of the importance of accounting for epidemiologic risks when evaluating a clinical syndrome, one can consider the case of a young woman who presents with diarrhea. She should always be asked if she has small children and if they are in day-care. The children can be the source for introduction of Giardia into the home, even though they may be asymptomatically infected.
Ova and Parasite Examination
Throughout the years, the standard diagnostic method for Giardia has been the stool examination for ova and parasites (O&P) (Burke, 1977; Thornton et al., 1983; Wolfe, 1992). This examination remains necessary and valuable when other parasitic causes of intestinal infection are being considered, or when the technology to perform antigen detection is not available. In an O&P exam the stool is usually examined fresh, and after fixation with polyvinyl alcohol or 10% buffered formalin. It may also be concentrated by formalin-ethyl acetate or zinc sulphate flotation to try to increase the yield.
A saline wet mount of a fresh, liquid stool may yield motile trophozoites as well as cysts; stools which are semi-formed will usually contain only cysts. Cysts may be more easily detected by mixing the sample with iodine, which will stain the cysts brown and highlight the intracystic structures. Fixed specimens can be stained with trichrome or iron hematoxylin and then examined (Figure 10.1A,B). Yields from an O&P exam are 50-70% for one stool and as high as to 90% after three stools (Hiatt et al., 1995).