ABSTRACT
The protozoan parasite Giardia lamblia was first identified by the Dutch microscopist Anton van Leeuwenhoek in 1681. Reporting his findings in a letter to the Royal Society in London, van Leeuwenhoek drew attention to the possible association between intestinal disease and the organism he had identified (1). Despite the implication of this observation, G. lamblia was regarded as a nonpathogenic commensal for nearly 300 years. Even as recently as the 1950s, studies of the transmission of G. lamblia suggested that the parasite was nonpathogenic. However, during the last three decades an increased recognition that diarrheal diseases are a major cause of morbidity and mortality throughout the world, particularly in developing countries, has prompted new interest in the etiology and pathophysiology of diarrheal diseases. As a consequence of this interest, G. lamblia has become the subject of intense investigation. Facilitated by major advances in the clinical and basic sciences, this investigation has resulted in the recognition that G. lamblia is capable of causing gastrointestinal disease ranging from asymptomatic cyst passage to severe diarrhea with malabsorption. Recent investigation also has provided important insights into the biology of the parasite. In addition, complex issues regarding the immunology and pathophysiology of giardiasis are now being addressed. The importance of this renewed interest in G. lamblia is underscored by the fact that this parasite has become the most frequently identified intestinal parasite in the United States and many other regions of the world. Although many questions remain unanswered, remarkable advances in understanding G. lamblia and the disease it causes have occurred since van Leeuwenhoek's insightful report to the Royal Society.
