Posted in Flagyl on December 31, 2014


Evolution is frequently cited as the core of biology no more than it has also been exhausted in mutable media outlets from television to newspapers and books. One highly popular children’s television program, Pokémon, shows manifold of the organisms known as Pokémon “evolving” into unlike forms which acquire a wide dress of new abilities that make them again successful than their previous forms. Understandably, much of the actual scientific meaning of development is lost in the show, bound the concept of turning into a modern form with new abilities often holds veritable in science. In this sense, the second nature the Pokémon “evolve” into a different form is actually a metamorphosis in some measure than evolution as is known in the according to principles context. One prime example, Giardia lamblia, likewise known as Giardia intestinallis or Giardia duodenalis, is a protozoan whose human infection life cycle revolves around the transfigure from the cyst form into the trophozoite form (Figure 1).

G. lamblia was elementary discovered in the seventeenth century and became suitable in the United States and Europe in the 1960s and 1970s (2). Transmission often occurs by ingesting food or irrigate contaminated with G. lamblia cysts unless can also spread directly through the fecal-vocal pathway which is characteristic of unfertile hygiene practices (2). One very peculiar feature of giardiasis, or the contagion with G. lamblia, is that the polluting G. lamblia trophozoites are confined strictly to the lumen of the scanty intestine which does not spread to the courage stream like many other protozoan infections (1). Due to the limited localization of this infection to the unimportant intestine, the major symptoms associated through giardiasis include severe, watery diarrhea and put up with cramps. It is now cited taken in the character of the leading cause for waterborne diarrhea in the United States (2). Approximately 5,000 persons are hospitalized annually in the US and millions of cases are reported globe-wide (2). One of the greatest part effective medications against giardiasis is metronidazole, that is a nitroimidaozole antibiotic medication (2). One of the explanation elements of this drug and in what condition it avoids harming human cells, is that it attacks the anaerobic pathways in G. lamblia what one. are essential for the protozoan’s survival. In giardiasis, this remedy ultimately damages the DNA of the catching trophozoite stage of infection and kills the protozoan in advance of it completes its life cycle and forfeiture the host.

Figure 1: G.lamblia life cycle.

The life cycle of G. lamblia be able to be split into two distinct phases; the latent, cyst phase and the infectious, trophozoite phase. The cysts of G. lamblia be in actual possession of been shown to be extremely elastic to a wide variety of environmental conditions and also have a metabolic degree of just ten to twenty percent of the trophozoite cast allowing them to survive for extended periods superficial of their hosts. This begs the point as to how the cyst shape of G. lamblia “evolves” into the trophozoite cut so quickly in the human landlord intestine. The first step in human bane is ingesting the resilient cysts (merely 10 required for infection) through contaminated furnish with ~ or food as stated above (2). Thereafter, the cysts have to travel through the digestive sermon, avoiding degradation till they reach the inferior intestine. There have been several studies in reference to the metamorphosis phenomenon which have construct that the shift in pH from the acidic taste to the slightly alkaline pH of the trivial intestine serves as a signal to vary the morphology and gene expression of the cyst which results in the formation of trophozoites (4). Hetsko et. al. place that it was likely that there was pre-made mRNA ready to be  translated whenever the cysts were exposed to the varying physiological pH transitions, which may encode for a variety of external part proteins such as adhesive molecules since localization in the small intestine (4). This “evolution” of the sac form of G. lamblia to the trophozoite is termed excystation or encystation depending steady the stage of infection (Figure 1).

After “evolving” into the vitiating trophozoite form due to the multiform pH signals in the digestive quarter, they start causing symptoms in individuals ~ means of localizing to the duodenum and the upper internal (2). Symptoms such as watery diarrhea, disproportionate flatulence, greasy stools, stomach cramps, and swelling are some of the most usual symptoms associated with giardiasis (1). However, it should subsist noted that giardiasis can be asymptomatic in the vulgar with strong immune systems and usually causes true severe symptoms only in immunocompromised individuals. It is hypothesized that the colonization of G. lamblia in the narrow intestine results in disease due to a kind of mechanisms such as: by the regulate damage of the human intestinal mucosa, end the release of cytopathic substances from the trophozoites, and/or that an immune response that results in the  excitement of the mucosa cells (2)(3). Finally the trophozoites’ extended stay in some alkaline pH in the small internal also serves as a signal as antidote to the encystation process which triggers metaphysis back into the dormant cyst figure which are excreted through the great intestine and ultimately in the feces circling back to the capital stage of the G. lamblia life circle of time (2)(4).

Just as Pokémon “evolve” into deviating forms with different characteristics, Giardia lamblia metamorphoses from its dormant, cyst form to an infectious, trophozoite fashion by sensing sudden physiological pH changes seen in the digestive parcel. This metamorphosis event is vital for the protozoa to cause disease in humans and finally complete its life cycle. Further discursive faculty of this mechanism of metamorphosis be possible to be vital in furthering treatment and interruption of this disease.


1)     Gardner, T., & Hill, D. (2001). Treatment of Giardiasis. Clinical Microbiology Review. 14 (1): 114-128.

2)     Adam, R. (2001). Biology of Giardia lamblia. Clinical Microbiology Review. 14 (3): 447-475.

3)     Faubert,G.(2000). Immune Response to Giardia duodenalis. Clinical Microbiology Review. 13 (1): 35-54.

4)     Hetsko, M., McCaffery, J., Svard, S., Meng, T., Que, X., and Gillian, F. (1998). Cellular and Transcriptional Changes During Excystation of Guard lamblia in vitro. 88 (3): 172-183.

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