were found in both humans and domestic animals (e.g., cattle, sheep, dogs). These and other facts support the conclusion that some strains of G. duo-denalis can be transmitted from vertebrate animals to humans and that giardiosis is a zoonosis. Humans are apparently the most important reservoir hosts and certain mammalian animal species are considered additional sources of infection.
The cysts excreted in stool are responsible for spreading the infection. They remain viable for up to three weeks in moist surroundings at 21 °C and up to about three months in cool water (8 °C). The trophozoites, by contrast, die off soon outside the host. Infection is per os, whereby cysts are transmitted by the fecal-oral route from person to person (within families, kindergartens, between homosexuals, etc.) or in food and drinking water. Numerous epidemic outbreaks of giardiosos due to contaminated drinking water have been described in the US and other countries with up to 7000 persons locally involved.
Pathogenesis and clinical manifestations. In the small intestine, G. intesti-nalis can cause inflammation as well as other morphological changes and malabsorption. Gallbladder infections have also been described. The patho-genesis is unclear; new data provide evidence that Giardia produce toxinlike proteins.
The course of infection is frequently asymptomatic. The parasite can be eliminated spontaneously within a few weeks; on the other hand, it may persist for years. The ability to produce variable surface proteins may influence elimination and persistence. Patients with symptomatic infections experience chronic and recurrent diarrhea, steatorrhea, and signs of malabsorption as well as upper abdominal pains, vomiting, occasionally fever, and weight loss.
Diagnosis, therapy, and prevention. The standard diagnostic method is stool examination using the SAFC technique to detect cysts and (more rarely) tro-phozoites (p. 621). Trophozoites can also be found in duodenal aspirate. IFAT and ELISA kits are now also available to detect Giardia-specific structural and soluble antigens in stool samples. Nitroimidazole compounds are used for chemotherapy of infections, for instance metronidazole, ornidazole, and ti-nidazole (see Table 9.5), as well as the benzimidazole compound albendazole and the recently introduced nitazoxanide (nitrothiazole compound). Prophylactic measures are the same as for amebosis (p. 499). A vaccine induces a reliably protective effect in dogs and cats.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.