Giardia lamblia Dr. Bimal Kumar Das Department of Microbiology All India Institute of Medical Scinces New Delhi-29 Source:

The genus Giardia belongs to the class Zoomastigophorea, the order Diplomonadida, and the family Hexamitidae. It is one of the most primitive eukaryotes: it has a small subunit ribosomal RNA sequence and no mitochondria and Golgi apparatus Now Giardia can be classified according to antigen, isoenzyme, and genetic analysis in addition to their morphology and host range. G. lamblia (also called intestinalis or duodenalis) is the species infecting humans.

Species identified Giardia lamblia (intestinalis, duodenalis) - humans, mammals Giardia muris - mammals Giardia ardeae - birds Giardia psittaci - birds Giardia agilis - amphibians

Cysteine-rich surface protein termed the variant specific surface protein responsible for antigenic variation within species These proteins may help to protect the parasite against the activity of intestinal proteases, as well as play a role in immune evasion. Of the Giardia species, only G. lamblia has been successfully cultured in vitro. The trophozoite divides by longitudinal binary fission Two morphological forms: Trophozoite and cyst ( infective form)

Tear drop shaped 2 adhesive discs, 2 median bodies, 2 nuclei 4 pairs of flagella Source:

intracytoplasmic projections axonemes Source:

Haematoxilyn staining two nuclei, each with a prominent central karyosome (characteristic facelike image ) Source: Gallery of histology Woods and Ellis2000

8 to 12 mm long and 7 to 10 mm wide convex dorsal surface a flat ventral surface sucking or adhesive disk four pairs flagellae Source:

Epidemiology Presumed to be zoonotic, but new evidence indicates that strains may be species specific. Host can be humans, primates, cats, dogs, calves, beavers, rabbits, etc. World wide distribution Highest incidence in children, young adults in late summer.

Transmission Person to person transmission Water sports, surface contamination. Watershed contamination sexually active male homosexuals and persons in custodial institutions.

Pathogenesis and Immune response (1) The production of diarrhea, and occasionally malabsorption, is the result of a complex interaction of Giardia with the host, Infection occurs after oral ingestion of as few as 10 to 25 cysts. After excystation, trophozoites colonize and multiply in the upper small bowel Adherence of G. lamblia in the human gut may be via the disk, but may also involve specific receptor-ligand interactions

Pathogenesis and Immune response (2) Several pathogenic mechanisms have been postulated Disruption of the brush border Mucosal invasion Elaboration of an enterotoxin Stimulation of an inflammatory infiltration leading to fluid and electrolyte secretion and occasionally to villous changes

TEM micrograph showing the method of attachment to the duodenal wall. Ventral sucking disc Source: Gallery of histology Woods and Ellis2000

Giardia Lamblia clinging to the wall of a duodenal villus. Source: Gallery of histology Woods and Ellis2000

Immune Response Partially protective immunity may develop to Giardia Immune response involves both cellular and humoral immunity Ig A, serum Ig G and Ig M are detected in patients: role of Ig A is not completely understood, probably inhibits trophozoite attachment IgA deficiency lead to chronic giardiasis Cell mediated immune response may also play a role Human milk may also play a role in protection of the host against Giardia : Free fatty acids and IgA antibodies

Infection with G. lamblia includes asymptomatic cyst passage (5 to 15% ) acute self-limited diarrhea (25 to 50% ) and a chronic syndrome of diarrhea malabsorption, and weight loss Symptomatic giardiasis is characterized by acute onset of diarrhea, abdominal cramps, bloating, and flatulence feelings of malaise, nausea, and anorexia may complain of sulfuric belching Vomiting, fever, and tenesmus occur less commonly. stools may be profuse and watery, but later they are commonly greasy, and foul-smelling and may float

The role that chronic infection with Giardia plays in the growth and development of children in the developing world has been controversial

Life Cycle Trophozoites : Lives in duodenum, jejenum and upper ileum They come in close contact to the mucosal, but do not invade the host. Adhesive disc fits over surface of epithelial cell The flagella act as a pump to move nutrients away from the microvilla and hold the adhesive disc near the mucosa. Rapid division to produce large numbers quickly

Source: Doug Allington

14 billion parasites in diarrheic stool (trophozoites only) Moderate infection: 300 million cysts. As the organism traverses the colon it is stimulated to encyst. Produce an oval cyst with thick walls, with 2-4 nuclei. Dividing within cyst (4 nuclei is older cyst) Complete division in duodenum of host after ingestion Cyst is approximately 8-10m and ellipsoid in shape. The cyst is the infective state and is transferred by the fecal- oral route.

Diagnosis Giardia should be identified 50 to 70% of the time after one stool, and 90% identification after three stools Wet, saline mounts: falling leaf motion, fibrils present, and nucleic characteristics. Biopsy tissue/duodenal aspirate stained by trichrome or Giemsa stain. Enzyme immunoassay and fluorescent-anitbody monoclonal antigen detection systems Sensitivity & specificity: % ( ProSpec T, GiardEIA, MeriFluor, Color Vue, and DD System)

Source:

Source: Doug Allington

Source: cbc.ca

DrugAdultPediatric Metronidazole250mgtidX 5-7 d5mg/kg/tid x 7 d Quinacrine100mgtidX5-7d2mg/kg tidX7d Furazolidone 100 mg qid × 7–10 d 2 mg/kg qid × 10 Paromomycin 25–30 mg/kg/d in 3 doses × 5–10 d Tinidazole 2 g × 1 dose

PREVENTION The prevention of giardiasis requires proper handling and treatment of water Good personal hygiene on an individual basis Chlorination alone is sufficient to kill G. lamblia cysts, important variables, such as water temperature, clarity, pH, and contact time, alter the efficacy of chlorine, and higher chlorine levels (4 to 6 mg/liter) may be required. Bringing water to a boil is sufficient to kill all protozoal cysts; at high altitudes, boiling for longer periods may be necessary

Artistic impression by Russel Kightley Source: