Giardia Lamblia, An Eukaryotic Pathogen

Giardia lamblia is a single-celled eukaryotic pathogen with flagella. The pathogen is known to enter the human body as a cyst in one of the life cycle phases, after which it settles in the intestinal system, causing diarrheal infections (CDC, 2021). The pathogen leads an attached lifestyle due to the adhesive disc by which Giardia lamblia adheres to the epithelial walls. The eukaryote feeds through the intestinal lumen, from which Giardia lamblia absorbs nutrients from the host. Cystic uptake is realized through contaminated water and food and through the host’s feces, whether human, domestic pets, or cattle.

Giardia lamblia was isolated in 1859 by Czech professor Lambl, but the pathogen did not receive its current name until 1915. There is controversy regarding the taxonometric naming of the pathogen, as Giardia lamblia is often referred to by authors as Giardia duodenalis, mainly due to the presence of a dual set of organelles within the cellular structure (CDC, 2021). Giardia lamblia was cultivated in 1959 by Karapetyan, who used yeast inoculation on human serum for cultivation (Karapetyan, 1962). Later, Gillin cultured the pathogen’s entire life cycle — the author discovered that the parasite could mask membrane proteins to prevent the host’s immune response (Shih et al., 2022). Giardia lamblia raises doubts regarding pathogen reproduction mechanisms. In particular, eukaryotes divide longitudinally by binary fission; however, there is speculation about sexual reproduction in Giardia lamblia based on the isolation from the pathogen isolate of meiotic recombination genes presumably responsible for sexual reproduction (Chen et al., 2021). Thus, whether Giardia lamblia has sex or what these genes are used for is still unknown. The NCBI describes the cellular and molecular structures of the pathogen (NIH, 2019). Giardia lamblia is reported to have five chromosomes, and the total genome size of the parasite is 12.1 Mb; the total number of genes is typical for a pathogen and is 5388.

The pathogen’s virulence factors are cysteine proteases, which degrade immune agents and host proteins. Giardia lamblia produces the molecules CRP136 and ESP58, which increase intestinal peristalsis (Ortega-Pierres & Argüello-García, 2019). Disease caused by the pathogen is seen through abdominal bloating, nausea, diarrhea, and decreased appetite, with the diagnostic method being a coprological culture test. Treatment is medicated with a course of antiparasitic drugs, such as metronidazole, while prevention includes food safety and hygiene procedures, as well as a diet at the first signs of the disease.


CDC. (2021). Pathogen and environment. CDC.

Chen, Y. C., Tung, S. Y., Huang, C. W., Gan, S. W., Lin, B. C., Chen, C. W.,… & Sun, C. H. (2021). A novel Spo11 homologue functions as a positive regulator in cyst differentiation in Giardia lamblia. International Journal of Molecular Sciences, 22(21), 1-13.

Karapetyan, A. E. (1962). In vitro cultivation of Giardia duodenalis. The Journal of Parasitology, 337-340.

NIH. (2019). Giardia intestinalis. National Library of Medicine.

Ortega-Pierres, M. G., & Argüello-García, R. (2019). Giardia duodenalis: Role of secreted molecules as virulent factors in the cytotoxic effect on epithelial cells. Advances in Parasitology, 106, 129-169.

Shih, H. W., Alas, G. C., & Paredez, A. R. (2022). A cell-cycle–dependent GARP-like transcriptional repressor regulates the initiation of differentiation in Giardia lamblia. Proceedings of the National Academy of Sciences, 119(22), 1-9.