Giardia lamblia (protist)

Giardia lamblia trophozoite (9)

Giardia lamblia cyst

Classification/Diagnostic characteristics
Domain: Eukarya
Kingdom: Protista
Phylum: Sarcomastigophora
Class: Zoomastigophora
Order: Diplomonadida
Family: Hexamitidiae
Genus: Giardia
Species: lamblia

• a diplomonad, a small zooflagellate (protozoan) that inhabits the digestive system of various animals
• unicellular, lacks mitochondria
• has two nuclei bounded by nuclear envelopes, a cytoskeleton, and multiple flagella
• pear shaped and has one or two claw-shaped median bodies (13)

Relationship to humans

• parasite that contaminates water supplies and causes the intestinal disease giardiasis
• one of the most common causes of waterborne disease in humans worldwide
• can cause chronic diarrhea and growth retardation in children of developing countries, more commonly infects children than adults, dangerous to those with malnutrition, immunodeficiencies, or cystic fibrosis (12).
• first protozoan parasite described, thought to be a harmless commensal organism of the intestine until 1970s, when it appeared in community outbreaks and travelers returning from developing countries (12)

Habitat and niche

• found in soil, food, water, or any surface that has been contaminated with feces from an infected animal
• can often be found in water that has not been boiled, filtered, or disinfected with chemicals
• After entering the host, it lives and reproduces in the small intestine, attaching itself to the epithelium using its ventral adhesive disc (2), a concave structure containing contractile proteins that aid in the organism's attachment (14).

Predator avoidance

• can switch surface proteins to avoid detection by the human immune system, making it difficult for human bodies to clear Giardia infection without drug treatment
• a protective outer shell protects it from disinfectants containing chlorine (8).

Nutrient acquisition

• uses a sucking disk to get nutrients from the mucous membrane of the small intestine of its host (2)
• aerotolerant anaerobe: doesn't require oxygen for cellular respiration and growth but is not harmed by oxygen. It relies on fermentation metabolism, a process that converts sugar to acids, gases or alcohol and leads to the production of energy. (15)

Reproduction and Life cycle/Growth and Development

• two stages: cyst and trophozoite
  • cyst:
    • approximately 7-10 µm in length, oval in shape, has
    • responsible for the disease transmission of giardiasis
    • after ingestion, the cysts, located in the small intestines, release trophozoites through a process called excystation
  • trophozoite:
    • approximately 7-10 µm in length and resemble a teardrop, have two distinct nuclei and four pairs of flagellae
    • responsible for producing the clinical disease in humans
    • colonize in the small intestine and can multiply through longitudinal binary fission, a form of asexual reproduction in which the parent cell divides into two identical daughter cells. The cycle repeats after the trophozoites move toward the colon.
    • trophozoites retreat back into their cyst stage in a process called encystation and new cysts are then excreted in the feces. (1)

(7)

Integument

• a tough outer shell enables it to survive outside the human body and also makes it resistant to disinfectants containing chlorine. (3)

Movement

• trophozoites have four pairs of flagella that allow the organism to move with a rotating motion
• the anterior and posterolateral flagellum act like oars to propel the body forward
• the ventral flagellum beat in a wave motion
• the flagella work together for directional control (18)

Giardia lamblia flagella

Sensing the environment

• pancreatic protease, cysteine protease CP2 and acidic conditions facilitate excystation
• the presence of fatty acid conjugated with bile salts and mildly basic conditions facilitate encystation (19)

Gas exchange

• occurs by diffusion, in which oxygen diffuses directly across the membrane and into the organism (10).

Waste removal

• after the food enters the cell and is digested in the vacuole, waste products are excreted by exocytosis, a process by which a vesicle inside the cell moves towards the plasma membrane and fuses with it, expelling its contents

Environmental physiology (temperature, water and salt regulation)

• lives and breeds in warm moist places, but because of its hard outer shell, it can survive in a variety of temperatures
• cysts can survive at temperatures as low as 4 degrees Celsius and as high as 25 degrees Celsius for several weeks, allowing it to inhabit soil, food, contaminated water, and feces. Depending on the substance they reside in, they can survive longer. For example, Giardia can survive 11 weeks in water, but only 1 week in cattle feces. (3,5)

Internal circulation

• no complex circulatory system because the organism is unicellular
• semipermeable membrane allows for nutrient intake and vesicles excrete wastes

Chemical control (i.e. endocrine system)

• no endocrine system because the organism is unicellular

Review Questions:
1.Why is Giardia Lamblia so dangerous to humans?
2. How can Giardia Lamblia survive in the human body despite the immune system?

References
1. http://www.giardiasis.org/Giardia-Lamblia.aspx2. http://davisjscientist5.blogspot.com/2008/02/giardia-lamblia.html3. http://www.cdc.gov/parasites/giardia/index.html
4. https://www.msu.edu/course/zol/316/glamtax.htm
6. http://www.phac-aspc.gc.ca/lab-bio/res/psds-ftss/giardia-lamblia-eng.php
7. http://upload.wikimedia.org/wikipedia/commons/thumb/d/db/Giardia_life_cycle_en.svg/619px-Giardia_life_cycle_en.svg.png8. http://www.cdc.gov/parasites/giardia/9. http://www.syncytiabeta.org/~syncyt5/syncytiabeta/images/c/ce/Giardia.jpg10. http://www.pcsd.k12.ny.us/bwoods/Regents%20Biology/Chapter%2011%20Gas%20Exchange/Chpter%2011%20Gas%20Exchange.htm11. http://water.me.vccs.edu/courses/env108/lesson6_2.htm12. http://emedicine.medscape.com/article/176718-overview13. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC88984/14. http://www.tulane.edu/~wiser/protozoology/notes/disk.html
15. http://www.ncbi.nlm.nih.gov/pubmed/6108507
16. http://www.dpd.cdc.gov/dpdx/images/ParasiteImages/G-L/Giardiasis/Giardia_cyst_wtmt3.jpg
17. http://www.answersingenesis.org/articles/am/v7/n1/magnificent-motors
18. http://www.ncbi.nlm.nih.gov/pubmed/21808023
19. http://microbewiki.kenyon.edu/index.php/Giardia_lamblia#Metabolism
BSCS Biology. a Molecular Approach. New York: Glencoe/McGraw-Hill, 2006. Print.