Giardia lamblia  

Contents/Objectives 1.Morphology. 2.Host. 3.Transmission. 4.Life cycle. 5.Intracellular metabolism and biochemistry. 6.Manifestation of infection. 7.Diagnosis &Treatment 8.Treatment in animals. 9.Prevention.

Morphology Giardia lamblia is a flagellated protozoan parasite that colonizes and reproduces in the small intestine, Causative agent of giardiasis. The parasite attaches to the epithelium by a ventral adhesive disc, Reproduces via binary fission. Giardiasis does not spread via the bloodstream, Remains confined in the lumen of the small intestine. Giardia trophozoites absorb their nutrients from the lumen of the small intestine, and are anaerobes.

Morphology cont… If the organism is split and stained, its characteristic pattern resembles the familiar "smiley face" symbol. Chief pathways of human infection include ingestion of untreated sewage Contaminated natural waters and in watersheds where intensive grazing occurs.

Hosts. Giardia infects humans, but is also one of the most common parasites infecting cats, dogs and birds. Mammalian hosts also include cattle, beavers, deer, and sheep

Transmission. Giardia infection can occur through ingestion of dormant microbial cysts in contaminated water, food, or by the faecal-oral route(through poor hygiene practices). The cyst can survive for weeks to months in cold water,so can be present in contaminated wells and water systems, especially stagnant water sources, such as naturally occurring ponds, storm water storage systems, and even clean-looking mountain streams.

Can also occur in city reservoirs and persist after water treatment, as the cysts are resistant to conventional water treatment methods, such as chlorination. Zoonotic transmission is also possible, so Giardia infection is a concern for people camping in the wilderness or swimming in contaminated streams or lakes, especially the artificial lakes formed by beaver dams (hence the popular name for giardiasis, "beaver fever"). Transmission

Transmission cont… In addition to waterborne sources, fecal-oral transmission can also occur, ie: in day-care centers, where children may have poor hygiene practices. Those who work with children are also at risk of being infected, as are family members of infected individuals. Not all Giardia infections are symptomatic, and many people can unknowingly serve as carriers of the parasite

LIFE CYCLE The life cycle begins with a noninfective cyst being excreted with the faeces of an infected individual. The cyst is hardy, providing protection from various degrees of heat and cold, desiccation, and infection from other organisms. A distinguishing characteristic of the cyst is four nuclei and a retracted cytoplasm.

LIFE CYCLE cont.. Once ingested the trophozoite emerges to an active state of feeding and motility. After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission. The resulting trophozoites and cysts then pass through the digestive system in the faeces. While the trophozoites may be found in the faeces, only the cysts are capable of surviving outside of the host.

LIFE CYCLE cont.. Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance. Cysts are distinguished by a retracted cytoplasm. Lacks mitochondria, although the discovery of the presence of mitochodrial remnants (organelles) in one recent study "indicate that Giardiasis not primitively amitochondrial and that it has retained a functional organelle derived from the original mitochondrial endosymbiont". This organelle is now termed a mitosome.

LIFE CYCLE

Colonization of the gut results in inflammation and villous atrophy Manifestation of infection. Colonization of the gut results in inflammation and villous atrophy Reducing the gut's absorptive capability. In humans, infection is symptomatic only about 50% of the time, and protocol for treating asymptomatic individuals is controversial fatal.

Manifestation of infection cont.. Symptoms of infection include (in order of frequency) diarrhea, malaise, excessive gas (often flatulence or a foul or sulphuric-tasting belch, which can be nauseating in taste hence vomiting) Steatorrhoea (pale, foul smelling, greasy stools), epigastric pain, bloating, nausea, diminished interest in food, possible (but rare) vomiting which is often violent, and weight loss. Pus, mucus and blood are occasionally present in the stool. It usually causes "explosive diarrhea" and while unpleasant, is not fatal

Treatment and diagnosis G. lamblia infection in humans is frequently misdiagnosed. Accurate diagnosis requires an antigen test or, if that is unavailable, an ova and parasite examination of stool. Multiple stool examinations are recommended, since the cysts and trophozoites are not shed consistently. Given the difficult nature of testing to find the infection, including many false negatives, some patients should be treated on the basis of empirical evidence treating based on symptoms.

Drug Treatment duration Possible side effects Metronidazole 5–7 days Metallic taste; nausea; vomiting; dizziness; headache; disulfiram-like effect; neutropenia Tinidazole Single dose 2 000 mg. Metallic taste; nausea; vomiting; belching; dizziness; headache; disulfiram-like effect

Nitazoxanide 3 days Abdominal pain; diarrhea; vomiting; headache; yellow-green discolouration of urine Albendazole 5 days Dizziness; headache; fever; nausea; vomiting; temporary hair loss.  

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