Giardia Life Cycle

The Giardia life cycle starts in contaminated water or food, where cysts are ingested and then transform into trophozoites in the host’s intestines. Understanding Giardia life cycle stages and transmission helps in implementing effective prevention strategies and minimizing the spread of this parasitic infection.

In this article, we will cover in detail the life cycle of Giardia and its diagram.

Giardia intestinalis is a protozoan flagellate (Diplomonadida) responsible for the disease giardiasis. Giardia is found in soil, contaminated food, or water, with the most common mode of transmission being water (drinking and recreational water). While the trophozoite stage can multiply outside a host for a short time under specific conditions, the complete life cycle of Giardia requires an in vivo (within a living host) environment.

Cyst ingestion starts the infection process in the host, followed by the parasite’s trophozoite form excysting and colonizing the small intestine. Among the most basic developmental processes in eukaryotes are encystation and excystation, and their characterization may provide crucial insights into more complex developmental processes.

Giardia has two stages in its life cycle: the cyst and trophozoite stage. Humans can contract the infectious stage of the cyst stage by consuming only around 10–25 cysts. When excystation occurs, these cysts mature into trophozoites. The life cycle starts with the formation of the cyst and then excystation process starts which creates two trophozoites and ends with encystation. After this, the process repeats itself again.

Let’s discuss in detail each stage involved in the Giardia life cycle:

Cyst – Stage 1

• Cysts are the resistive form that is responsible for the transmission of giardiasis.
• There are diagnostic stages of both cysts and trophozoites in the faeces.
• The cysts can last several months in cold water due to their resilience.
• Cysts can infect people by food, water, or the fecal-oral route, which involves touching contaminated hands or feet.

Excystation – Stage 2

• In the presence of pancreatic enzymes (chymotrypsin and trypsin) and gastric acid, excystation takes place in the duodenum and stomach.
• Excystation requires an acidic environment with a pH between 1.3 and 2.7.

Trophozoites – Stage 3

• After ingestion, Giardia cysts excyst in the small intestine, usually the duodenum, releasing two trophozoites.
• The timing of excystation varies, influenced by factors such as stomach acidity.
• Trophozoites multiply within the intestine through binary fission.
• They attach to the intestinal lining (enterocytes) using their ventral suckers.
• In a favourable environment with bile salts and a slightly acidic to neutral pH, some trophozoites encyst in the large intestine.
• These cysts are shed in feces and can survive in the environment for extended periods, potentially perpetuating the transmission cycle.

Encystation – Stage 4

• The cytoplasm of trophozoites contains encystation-specific secretory vesicles (ESVs), which signal the start of the encystation process. Within 15 hours, the cyst wall is produced.
• These cyst wall proteins cover the trophozoite within 24 hours after the ESVs appear, causing a cyst to form.
• Cyst formation starts with the flagella’s shortening, followed by cytoplasm condensation and the thick hyaline cyst wall secretion.
• After undergoing another round of nuclear division, these encysted trophozoites develop into adult cysts with five nuclei.
• The parasite’s infectious cysts are expelled in faeces and undergo a repeating life cycle.

The scientific classification of Giardia is given below:

It exists in 2 morphological forms-

• Feeding/ Trophozoite stage
• Infective Cyst stage

Feeding/ Trophozoite Stage

Giardia intestinalis causes sickness through its trophozoites stage. This cell is around 12 to 15 μm length and 5 to 9 μm broad, giving it the appearance of a microscopic half-pear. The two nuclei of the trophozoite are symmetrically positioned in the anterior area.

• The parasite’s colonization of the intestine occurs during its active feeding stage.
• Trophozoites are shaped like pears or tennis rackets.
• The ventral surface has an adhesive disc and is concave, whereas the dorsal surface is convex.
• Every bodily organ is paired, and it is bilaterally symmetrical. They have two axostyles, two median bodies, two nuclei, and four pairs of flagella.
• Each nucleus is made up of a sizable central karyosome, which gives the parasite in stained preparation a distinctive face-like appearance.
• The motility displayed the usual falling leaf-type motility.
• On the ventral surface of the broad or anterior end, there is a bean-shaped sucking disc.

Cyst (Infective Stage)

Humans can contract the infectious stage of the cyst stage by consuming as low as 10–25 cysts. Once excystation occurs, these cysts mature into trophozoites.

• It is an infective stage of a parasite.
• A fully mature cyst is oval or ellipsoidal in shape and measures 8-13 micrometre in length and 7 – 10 micrometre in breadth.
• The cyst is surrounded by a thick cyst wall. There is a clear space separating the granular cytoplasm from the cyst wall.
• The axostyle lies more or less diagonally.
• A cyst contains 4 nuclei.
• A remaining flagella and the margins of the sucking disc may be seen inside the cytoplasm.
• Each cyst gives rise to two trophozoites during excystation in the intestinal tract.

A large number of trophozoites are attached to the bowel wall with the help of sucking discs that are present on the ventral surface of giardia lamblia and cause irritation. Low-grade inflammation of duodenal or jejunal mucosa is associated with crypt hypertrophy as well as atrophy and epithelial cell damage leading to acute or chronic diarrhoea.

Mode of Transmission

• Man is the main reservoir of Giardia.
• Infection is acquired due to:
  • Consumption of infected food or water is the cause of infection.
  • Spread from person to person as a result of unsanitary conditions in nursing homes, daycare centres, and mental asylums
  • Oral-genital and oral-anal sex as a means of sexual transmission.
• Giardiasis is more common in immunocompromised people, such as AIDS patients and those suffering from protein-energy deficiency.

Symptoms of Giardiasis 

The symptoms of Giardiasis include:

• Abdominal pain, cramp, dysentery.
• Rarely blood and mucus in stool.
• Chronic symptoms- malabsorption of B12, lactose intolerance, etc.

Diagnosis of Giardiasis 

The diagnosis of Giardiasis occurs by:

• The usual procedure for diagnosing giardiasis involves looking for cysts or trophozoites in stool samples. Since cyst excretion occurs sporadically, it is necessary to get numerous stool samples (at least three samples taken on different days) to exclude giardiasis.
• Giardia antigen tests have strong sensitivity (85 to 98%) and specificity (90 to 100%) and can be run on stool samples. These come in the form of immunoassays, such as fast tests (immunochromatographic tests) or ELISA (enzyme-linked immunosorbent assays).
• Although PCR may be a more sensitive method than microscopy or immunoassays for detecting Giardia-specific genes, most clinical laboratories do not regularly offer this service.

Treatment of Giardiasis 

Treatment options are:

• Fluids and rehydration for supportive therapy.
• In some cases, giardiasis goes away on its own without medication.
• If symptoms are severe or persistent, medication may be prescribed by a doctor.

Prevention of Giardiasis 

The preventions are:

• Frequent and thorough handwashing is essential, especially after using the toilet, changing diapers, and before preparing food.
• When outdoors, filter or boil drinking water from untreated sources like streams or lakes.
• Avoid swallowing pool, lake, or stream water while swimming.
• If traveling to areas with high giardia risk, consider bottled water for drinking and avoid using tap water for brushing your teeth.
• Practice safe sex, including condom use, to prevent transmission.
• Thoroughly clean and disinfect surfaces that may be contaminated with feces, especially in childcare settings.

Note:

Sometimes G.lambilia can also localizes in the biliary tract to causes cholecystitis and jaundice.

In conclusion, Giardia intestinalis, a microscopic parasite, causes giardiasis through a complex life cycle with cyst and trophozoite stages. Ingestion of cysts initiates infection, followed by excystation in the small intestine where trophozoites multiply and attach to the intestinal lining. Favourable conditions trigger encystation, and these cysts are shed in feces, perpetuating the cycle. Understanding Giardia’s life cycle and transmission routes is crucial for prevention and treatment.

Also Read:

• Difference Between Coccidia and Giardia
• Major Diseases Caused By Protozoans
• Chicken Life Cycle – Stages, Facts and FAQs
• Snail Life Cycle
• Mayfly Life Cycle
• Ant Life Cycle
• Life Cycle of Dragon Fly: Diagram, & Stages

What are the Symptoms of Giardiasis?

Diarrhea. Gas, Foul-smelling, greasy poop that can float, Stomach cramps or pain, Upset stomach or nausea, Dehydration.

Is Giardia a Virus or Bacteria?

Giardiasis is an infection in your small intestine. It’s caused by a microscopic parasite called Giardia lamblia. Giardiasis spreads through contact with infected people.

Why is Giardia Harmful?

Giardiasis is caused by the tiny Giardia parasite. The parasite attaches itself to the lining of the small intestines in humans, where it causes diarrhea and blocks the body’s absorption of fats and carbohydrates from digested foods.

How to Prevent Giardia?

Consumers can prevent giardiasis by: washing hands carefully, avoiding swallowing recreational water, using caution when traveling, avoiding drinking untreated water or treating water before drinking, being careful when dealing with animals, avoiding fecal exposure.

Where is Giardia Most Commonly Found?

Giardia is a water-borne parasite that is most commonly found in swimming pools, water supplies, lakes, ponds and wells.

What Does Giardia Feces Look Like?

Since this parasite causes chronic diarrhea, the feces excreted is greasy, watery and has a foul smell. Bloating and loss of appetite are some other changes caused by giardia.