Giardia Infections

Despite the controversy about the taxonomy of the species in the genus Giardia, this protozoan (G. in-testinalis/lamblia/duodenalis) produces an important disease in the proximal portion of the small intestine, which could be asymptomatic, produce an acute self-limited diarrhea, and diverse intestinal symptoms such as chronic diarrhea, abdominal pain, cramps and tenderness, and weight loss, among others. Normally, there is no extraintestinal infections, but sometimes could produce a reactive arthritis (in recent years different studies revealed a clear relationship between giardiasis and inflammatory processes and allergy, possibly because infection by this protozoon enhances sensitization toward food antigens, due to increased antigen penetration through damaged intestinal mucosa). In severe Giardia infections, significant lesions of duodenal and jejunal mucose cells also are seen. Although many aspects of the infection are currently known, the mechanisms of pathogenicity and the major host defenses against Giardia infection are not well characterized.

This infection could lead to intestinal malabsorption that may be severe, and when it occurs in children, it could be associated with growth and development retardation. This pathogen has a considerable prevalence either in institutional and community settings.

This parasite, described in 1859 by Lambl, is a flagellated eukaryote organism (which belongs to the subphylum Mastigophora) with a relatively simple life cycle which includes trophozoites (vegetative stage) and cysts (infective stage). Humans can carry both forms, as can animals, and today, giardiasis is considered a zoonosis.

Diagnosis of Giardia infections is made by examining stools of suspected individuals or animals (including direct and stained observations as well as cultures of the organism); however, sometimes this is not enough and other diagnostic techniques should be used (immunological and molecular tests), even to the extent of studying the duodenal contents. Giardia can also be diagnosed when organisms are seen in intestinal biopsy specimens and/or at endoscopic evaluations.

The choice treatment for this infection is tinidazole or nitazoxanide. Alternative treatments may include metronidazole and paromomycin. In refractory patients, metronidazole and quinacrine may be used.

As with most infectious and parasitic diseases, prevention is the most important issue. In the case of giardiasis, safe water access is one of the primary priorities that should be considered, because cysts could be viable for a long time in water contaminated by human and animal feces. Additionally, as giardiasis is common in children, health education, especially in primary schools, is useful in preventing this infection.

Recently, the importance of this pathogen for travelers to zones with high prevalence of this parasitosis has been highlighted.

Finally, molecular tools that are now available will be useful in better understanding the frequency of zoonotic transmission as well as in developing more effective approaches to controlling giardiasis.