Medical Parasitology - Lecture 3: Giardia lamblia PDF

Charmo University COLLEGE OF SCIENCE Department of Medical Laboratory Science Medical parasitology -Lecture 3 Intestinal Flagellates Protozoa/...

Charmo University COLLEGE OF SCIENCE Department of Medical Laboratory Science Medical parasitology -Lecture 3 Intestinal Flagellates Protozoa/ - Giardia lamblia Sunday, November 3, 2024 1  2- Protozoa: Class (Flagellates) o Parasitic protozoa, which possess whip-like flagella as their organs of locomotion are called flagellates o Flagella are slender, long and thread-like extensions of cytoplasm o Flagella arise from kinetoplast (made up of copies of mitochondrial DNA) o They are grouped into intestinal, genital and blood flagellates based on their habitat Protozoa Intestinal Blood & Tissue Urogenital Leishmania spp. E. Histolytica Trypanosoma spp. Trichomonas Giardia lamblia Plasmodium spp. vaginalis Cryptosporidium Toxoplasma spp. Most Luminal flagellates are nonpathogenic commensals Two of them cause clinical diseases Giardia lamblia, which can cause diarrhoea & Trichomonas vaginalis, which can produce vaginitis and urethritis. 2 Depending on Flagellates habitat, they can be considered under: o Lumen-dwelling flagellates: Flagellates found in the alimentary tract and urogenital tract. o Hemoflagellates: Flagellates found in blood and tissues. Sunday, November 3, 2024 3 Table: Flagellates Groups  History & Distribution of Giardia lamblia Giardia lamblia (Also known as Giardia intestinalis, Giardia duodenalis) o It is one of the earliest protozoan parasites to have been recorded. o It is the most common protozoan pathogen and is worldwide in distribution. o Endemicity is very high in areas with low sanitation, especially in the tropics & subtropics. o Visitors to such places frequently develop traveller's diarrhoea caused by giardiasis through contaminated water. Habitat of Giardia lamblia: G. lamblia lives in the Duodenum & upper Jejunum and is the only protozoan parasite found in the Lumen of the human small intestine. Sunday, November 3, 2024 4 Figure: Giardia lamblia  Giardia lamblia General characteristics of the Giardia lamblia:  It is found on surfaces or in soil, food, or water contaminated with faeces from infected humans or animals.  Giardia infection is the most common intestinal parasitic disease affecting humans in the US.  Giardiasis can cause weight loss and failure to absorb fat, lactose, vitamin A & B12.  IgA-deficient people are more susceptible. o G. lamblia infects humans and other mammals, G. muris in mice, G. agilis in amphibians, and G. psittaci in birds. o G. lamblia is worldwide in distribution. It is considered one of the most common parasitic diseases, causing both endemic and epidemic intestinal disease and diarrhoea. o The habitat of G. lamblia Duodenum and upper part of jejunum. o The Trophozoite has one nucleus, four pairs of flagella, and an axoneme. o Giardia cyst is oval-shaped. It contains four nuclei and remnants of axonemes. o Cyst is the infective form as well as the diagnostic form of the parasite. Sunday, November 3, 2024 5  Morphology of the Giardia lamblia Trophozoites -Trophs (or vegetative form) o 2 large nuclei & 8 flagella, median bodies. o They are motile with a slow oscillation about its long axis, often resembling “falling leaf”. o They are in the shape of a tennis racket; Pear or pyriform shaped & is rounded anteriorly and pointed posteriorly o Dorsally it is convex & ventrally; it has a concave large adhesive sucking disk, which helps in its attachment to the intestinal mucosa. o Measure 10-20 micrometers in length; Only bilaterally symmetrical protozoa. Trophs of G. lamblia A/ Saline mount ; B/ Giemsa stain Cysts (or cystic form) o The cysts are small & oval to ellipsoid, surrounded by a hyaline thick, refractile cyst wall. o Its internal structure includes 2-4 nuclei depending on maturity & grouped at one end. o Central fibrils (Axo style down the middle). o It is Non- motile, infective stage of the parasite o Measure 8-12 µm long x 7-10 µm wide. 6 Cyst of G. Lamblia; A/ Saline mount ; B/ Iodine mount ; C/ Trichrome stain  Forms of Giardia lamblia Diagram of the Giardia lamblia shows A the ventral & B the lateral views of the Trophozoite & C the Quadrinucleate Cyst Sunday, November 3, 2024 7  Mode of transmission of Giardia lamblia Man acquires infection by ingestion of food and water contaminated with mature cysts. o Direct person-to-person transmission may also occur in children, rarely in male homosexuals and mentally ill persons. o Enhanced susceptibility to Giardiasis is associated with blood group A, achlorhydria, use of cannabis, chronic pancreatitis, malnutrition, and immune defects such as 19A immunoglobulin deficiency and hypogammaglobulinemia. o Excystation: The cyst hatches into two Trophozoites in the duodenum within half an hour of ingestion,. o Multiplication: The Trophozoites multiply successively by longitudinal binary fission and colonize in the duodenum o Adhesion: The Trophozoites adhere to the duodenal mucosa and upper part of the jejunum, feeding by Pinocytosis. o Encystation: During unfavorable conditions, the Trophozoites pass down to the large intestine and begin promoting factors for encystation of the conjugated bile salts, alkaline pH and cholesterol starvation o Cysts are passed in stool and remain viable in soil and water for several weeks. o There may be 200,000 cysts passed per gram of faeces. The infective dose is 10-100 cysts 8  Life cycle of Giardia lamblia Life cycle of the Giardia lamblia Sunday, November 3, 2024 9  Symptoms (Clinical Features) of Giardia lamblia Clinical course of giardiasis can be divided into three stages:  Asymptomatic carriers: They are often asymptomatic.  Acute Giardiasis: Incubation period varies from 1 week to 3 weeks (average 12–20 days). Symptoms: In some cases, Giardia may develop suddenly or gradually, the common symptoms include diarrhea, dull epigastric pain, bloating, belching, flatulence and vomiting, diarrhea is often foul smelling with fat and mucus but No blood.  Chronic Giardiasis: It may present with or without a previous acute symptomatic episode. Children may develop chronic diarrhoea, malabsorption of fat, vitamin A, protein, sugars like xylose and disaccharides, weight loss, and sprue-like syndrome. Notes: Giardiasis is different from Amebiasis and bacterial dysentery No mucus, no blood, no granulocytosis and no fever. Sunday, November 3, 2024 10  Pathogenicity of Giardia lamblia  Infective dose: as few as 10–25 cysts can initiate the infection.  Risk factors: Children are commonly affected.  Other high-risk groups are elderly debilitated persons and patients with cystic. Several pathogenic mechanisms have been postulated include: o Trophozoites of G. Lamblia adhere to the duodenal mucosa and disrupt the intestinal epithelia. o They may cause abnormalities of villous architecture by cell apoptosis and increased lymphatic infiltration of lamina propria. o Giardia undergoes frequent antigenic variation due to a cysteine-rich protein on its surface called Variant- Specific Surface Proteins (VSSP); It plays a critical role in the virulence and infectivity of the parasite. o Very rarely, elaboration of enterotoxin such as cystein-rich surface protein 136 (CRP-136). o Fat Malabsorption (steatorrhea). o Occasionally, giardia may colonize the gall bladder, causing biliary colic and jaundice. Sunday, November 3, 2024 11  Investigations & Laboratory Diagnosis of Giardia lamblia 1)- Microscopic Examination (Stool Examination): Giardiasis can be diagnosed by identification of oval cysts of Giardia lamblia in the (formed faeces) and the motile Trophozoites and cysts of the parasite in (diarrheal faeces) by saline and iodine wet preparations.  Macroscopic examination: faecal specimens containing G. lamblia may have an offensive Odour, pale coloured and fatty and float in water. 2)- Antigen detection Assays (Fecal antigen detection) by Immuno Fluorescent Antibody (IFA) & Enzyme-Linked Immuno Sorbent Assay (ELISA), against cyst or Trophozoite antigens. 3)- Examination of Duodenal contents by aspiration and Biopsies from the upper small intestine. 4)- Enterotest (String Test): 5)- Molecular Method: by using DNA probe; PCR. Technique. Sunday, November 3, 2024 12  Entero test (string test) The Entero-test o It uses a gelatin capsule attached to a thread. One end of the thread is attached to the inner aspect of the patient’s cheek and then, the capsule is swallowed. o Capsule gets dissolved in the intestine releasing the thread which is kept there for 4-6 hours to take the duodenal fluid. o Later, the thread is withdrawn and shaken in saline to release Trophozoites which can be detected microscopically. The Entero-test is also useful in the search for other upper intestinal parasites o This test is performed if the physician suspects a parasitic infection but no parasites were found in the stool. Sunday, November 3, 2024 13  Treatment of Giardiasis  Metronidazole (250 mg thrice daily for 5-7 days).Cure rates with Metronidazole are more than 90%  Tinidazole (2g single dose orally) are the drug of choice. Tinidazole is more effective than Metronidazole  Furazolidone & Nitazoxamide are given to children as they have fewer adverse effects.  Parmomycin: an oral aminoglycoside can be given to symptomatic pregnant females. Note: Only symptomatic cases need treatment. Sunday, November 3, 2024 14  Prevention of Giardiasis Prophylaxis Giardiasis can be prevented by following measures:  Proper disposal of wastewater and faeces.  Practice personal hygiene like hand-washing before eating & proper disposal of diapers.  Boiling or filtration of potentially contaminated water by membrane filters are required. Community Chlorination of water is Ineffective for inactivating cysts.  Treatment of asymptomatic carriers.  No vaccine is currently available. Sunday, November 3, 2024 15