The protozoan Guardia duodenalis or Giardia lamblia is an intestinal parasite living in domesticated animals like dogs and cats, in beavers, in livestock animals such as cattle and pigs, and even in humans (Centers for Disease Control and Prevention 2008). This parasite was first observed by Anton van Leeuwenhoek in 1861 and named after the Prof. A. Giard and Dr. F. Lambl in 1915 (Rockwell 2003). For the past two decades, G. lamblia infection became a typical cause of waterborne illness in the United States (Centers for Disease Control and Prevention 2008).
According to the World Health Organization (WHO), 250 million citizens around the world are infected by Giardia (Daniel Palm et al. 2003). Through fecal excrements of the infected animal or individual, water, soil or food can be contaminated with Giardia. Thus, other humans and animals can be infected by Giardia by means of direct contact with these carriers resulting to Giardiasis (Centers for Disease Control and Prevention 2008). G. lamblia Infections G. lamblia is ubiquitous in natural water, waste water, and even in municipal water supply in most cities of the United States (Rockwell 2003).
Based on reports, around twenty percent of the world population was infected by Giardia including four to seven percent of American population without Giardiasis symptoms (Rockwell 2003). Specifically, the Center for Disease Control and Prevention of The United States estimated that 2,500,000 Americans have giardiasis or around one hundred persons annually are infected by Giardia. At worst, fifty percent of the day care centers’ populations across all regions were infected (Rockwell 2003).
Giardiasis cases have also been observed in Asian, Latin American, and African countries (Rockwell 2003). This infectious disease has several intestinal symptoms like nausea or stomach upset, abdominal cramps, diarrhea, flatulence, and greasy feces that may result to dehydration or decrease in weight (Centers for Disease Control and Prevention 2008). These symptoms may develop among the infected individuals or animals after seven days or within two weeks (Centers for Disease Control and Prevention 2008).
Also, most parasite-induced cases of diarrhea in the North America were attributed with Giardia protozoans (Rockwell 2003). Researches revealed that the variation in the clinical symptoms of Guardia infection are primarily affected by the host’s immunity, the actual cyst ingested, the age of the host, and the parasitic strain (Daniel Palm et al. 2003). Infected individuals develop symptoms while others are asymptotic. Moreover, clinical symptoms depend largely on immunological factors of the patient while its severity is ascribed with G.
lamblia’s antigenic variation (Muller and von Allmen 2005). Luckily, severe giardiasis symptoms such as stomach trouble, decreased weight, and malabsorption was only noted from less than one percent of the infected cases (Rockwell 2003). G. lamblia Transmissions Contaminated Water is one of the point sources of Giardia infection; however, solid evidences also speak for person to person and animals to person transmissions (Muller and von Allmen 2005). For instance, a “fecal accident” in a public swimming pool in New Jersey has caused Giardiasis among nine swimmers (Rockwell 2003).
It was estimated that around 900 million cysts can be shed by an infected individual through fecal excretion (Rockwell 2003). Thus, Municipal water facilities are required to use filters for Giardia removal (Rockwell 2003). On the other hand, infection can also be transmitted by means of foods. For example, in Connecticut, sixteen people were infected by Guardia by eating salad during their picnic (Rockwell 2003). The Center for Disease Control and Prevention found out that the salad was infected by Guardia through the hands of the woman who prepared it.
Even though the woman has no infection, but her child has asymptotic Giardia case (Rockwell 2003). Similar to this case, a salad preparer was detected as positive with the infection, as well as her child and their rabbit (Rockwell 2003). In this connection, evidences against pet animals as the means of infection transmission were reported. As an example, in 1993 at Tibet, a mountain climber was diagnosed with giardiasis after the climbing expedition (Rockwell 2003). Since all their foods were prepared by Sherpa cooks with good hygiene, it was presumed that beavers brought Giardia in glacial melt which was their water source (Rockwell 2003).
In relation to this, it was postulated that humans, the real parasite carriers, brought Giardia into the mountain high which then infected beavers (Rockwell 2003). This assumption was supported by research data showing high cases of giardiasis among beavers near the camp places as compared with those living afar (Rockwell 2003). Transmission Cycle G. lamblia has flagellae for attachment, absorption, and locomotion. This protozoan adheres with the upper tract lining of the intestine of the host species, absorbs nutrients and reproduces (Rockwell 2003).
In the intestinal sites, trophozoites tightly adhere into the lining tract which paralyzes the intestines’ enzyme secretion and food absorption (Rockwell 2003). Meanwhile, in its active form or trophozoite, it undergoes binary fission every 12 hours (Rockwell 2003). With this reproduction rate, a Giardia within ten days may become more than a million and exponentially grow into a billion within fifteen days (Rockwell 2003). As the trophozoite incorporates with the feces excretion, it changes into a cyst having an egg-like shape (Rockwell 2003).
This structure enables the Giardia to survive even after several months outside the host until such time that a new animal or human picks it up with objects contaminated with the host stools (Rockwell 2003). Then, by means of enzymatic and acid reactions in the body of the new host, Giardia transforms back into trophozoite (Rockwell 2003). A trophozoite has nine to fifteen microns length, five to fifteen microns width and two to four microns thickness while a cyst may only have eight to twelve microns length, six to nine microns diameter (Rockwell 2003).
Even though cysts may withstand cold water for two to three months, they can not survive at freezing temperatures. Also, radiation, bleach and other biocides annihilate their population (Rockwell 2003). Diagnosis and Medication Although scientists have been exploring the physiological and immunological factors involve in host and G. duodenalis interplay, the full mechanism of parasite infection has not yet been fully known (Muller and von Allmen 2005). Meantime, the traditional microscopic examination of trophozoites in feces has been replaced nowadays by Enzyme-Linked Immunosorbent Assay or ELISA in Giardia antigen detection (Rockwell 2003).
The presence of Giardia antigens is a confirmatory for the infection. The ELISA method has more than 90 percent detection sensitivity far greater then the traditional microscopy (Rockwell 2003). Although Metronidazole has been tested with 92 percent clinical efficacy for Giardia severe cases, this drug was not approved by the Food and Drug Administration of the United States because of its carcinogenic potential and side effects (Rockwell 2003). Other prescribed drugs were Tinidazole, Quinacrine, and Furazolidone (Rockwell 2003). Conclusion
Since past studies have delved on in vitro or in vivo co-cultivation of the parasite in epithelial cells or experimental hosts, future researches should dwell on the cellular mechanism of the immune system concerning the parasite-host interaction (Muller and von Allmen 2005). In fact, as recommended by recent study, the mechanism of inflammatory reaction of the intestine should be further explored for this process was reported to significantly determine the physiological and immunological conditions of the parasite in the intestinal tract lining (Muller and von Allmen 2005).
In line with this, the researches on the growth and propagation of G. duodenalis under inflammatory conditions are expected to provide a plausible basis on the possibility resistance development against the infection brought by the parasite (Muller and von Allmen 2005). Hence, for the time being, let us observe strict discipline in hygienic practices especially in handling foods and be cautious in the maintenance of our pets’ health and cleanliness, and environmental sanitation as preventive measures against any dreadful disease. References Centers for Disease Control and Prevention.
Giardiasis. 2008 November 12. Division of Parasitic Diseases. Available from http://www. cdc. gov/ncidod/dpd/parasites/giardiasis/factsht_giardia. htm Accessed 2009 February 16. Daniel Palm JE, Weiland Malin EL, Griffiths WJ, Ljungstro I, and Sva SG. 2003. Identification of immunoreactive proteins during acute human giardiasis. The Journal of Infectious Disease 187: 1849-1859. Muller N and von Allmen N. 2005. Invited Review: Recent insights into the mucosal reactions associated with Giardia lamblia infections. International Journal for Parasitology 35: 1339-1347.