Giardiasis, also known as “traveler's diarrhea,”  is caused by Giardia intestinalis. Other names for this parasite are Giardia lamblia, and Giardia duodenalis. There are many different genetic assemblages of this parasite, some that infect only mammals, some that infect primarily humans, and a few that will affect both animals and man. 
While G. intestinalis “can live in the intestines of animals and people” it is very rare for a human to acquire such an infection from their cat or dog. ,  The Giardia parasite can survive in “soil, food, and water.”  Transmission most frequently occurs when one ingests untreated water that has been contaminated by animal waste. It can also be contracted through direct contact with an infected person, consumption of raw/undercooked, contaminated meat, or sexual contact. , 
As previously mentioned, there are multiple different types of G. intestinalis. These are sometimes categorized further into subtypes. For example, A-II infects only humans, and is more often seen than A-I (which can infect a variety of animals including dogs, cats and livestock; as well as humans). However, A-III and A-IV are seen only in animals. 
Specific Characteristics of Microbe:
Giardia intestinalis is classified as such: 
intestinalis (or duodenalis, lamblia)
There are two stages of life for the protozoal Giardia parasite. The trophozoite phase, and the cyst phase. In order to infect a host, the cyst phase of the uni-cellular organism must be ingested. Once in the stomach, the acidic environment activates the cyst and it releases trophozoites (the active form of G. intestinalis within the body).  The trophozoite form is very easily identified by it's face-like arrangement of nuclei (resembling eyes) and median bodies (forming a structure appearing as a mouth), as well as its four flagella. These flagella assist the parasite in attaching to the lining of the small intestine, where it reproduces and releases cysts (which are thus expelled through one's fecal matter to search for a new host to infect). These cysts are oval in shape, and sometimes two to four nuclei can be seen at one end. , 
Tests for Identification:
In order for a negative result to be reported, at least three stool samples collected on different days must be tested. Tests for identification of Giardia intestinalis include a “direct florescent antibody (DFA) assay,” an “enzyme immunoassay (EIA),” or “rapid immunochromatographic cartridge assays.” The most common and specific test is the DFA assay. Known as the laboratory's golden standard test, antibodies are tagged with markers and incubated with a stool sample. When viewed under a microscope, Giardia cysts appear as florescent green “ovoid objects.”  The rapid immunochromatographic assay is the quickest and often said to be easy to perform. However, any borderline reading must be reconfirmed by a DFA assay to ensure accurate reportings. 
Another major test utilized to identify Giardia is the stool ova and parasite exam. When one receives a negative result, this means there are no parasites or eggs in the sample, and so no infection. This test is used to diagnose general parasitic infection, and does not identify which parasite eggs are within the stool sample. 
Signs and Symptoms:
It is very possible to be asymptomatic when infected with Giardia. There is an incubation period of at least 7 days, and rarely more than 14 days, in which symptoms of infection are delayed. The primary symptom of infection is diarrhea, but other complications may present themselves. These include bloating, abdominal cramping, nausea and gas. Dehydration and extreme weight loss are possible in a...
References:  Centers for Disease Control and Prevention. “Parasites – Giardia.” Last reviewed March 8th, 2011. http://www.cdc.gov/parasites/giardia/. 3/5/14.
 John Hopkins Medicine Health Library
 Vorvick L. J., Vyas J. M. and Zieve, D. “Giardia Infection.” Last updated May 30th, 2012. http://www.nlm.nih.gov/medlineplus/ency/article/000288.htm. 3/5/14.
 Gargano J. W., Yoder J. S. “Giardiasis.” Last updated August 1st, 2013. http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-3-infectious-diseases-related-to-travel/giardiasis. 3/5/14.
 Cowan, K. (2010). Microbiology: a systems approach. (2nd ed., pp. 138, 389t, 711-12). Boston: McGraw-Hill Companies, Inc.
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