Giardiasis is a chronic, intestinal, protozoal infection seen around the world in most mammals, many birds, and people too. As such it is a Zoonosis, infection is common in dogs, cats, ruminants, pigs, and the highest rates of infection are seen in young animals. Giardia species are found in mice, amphibians, and warm-blooded vertebrates. The species complexes infecting vertebrates include G Ardea and G Psitta from birds. G MicrotiI from muskrats and voles and G Duodenalis also known as G Intestinalis and G Lamblia which has a wide mammalian host range. As flageolet protozoan trophozoites Giardia attached to the brush border of the intestine, usually the proximal small intestine. Upon encystation in the smaller large intestine cysts then pass in the faces squared as infective and can survive for weeks in the environment.
The pre-Payton period is generally 2 to 10 days, sis shedding may be continued over several days over a week, but is often intermittent, especially in the chronic phase of infection. Within this scheme obviously Giardia via injunction of materials contaminated by feces. Only smaller numbers of cysts are needed to initiate infection. High humidity facilitates the survival of cyst in the environment and animal overcrowding facilitates transmission. A not uncommon means by which humans become infected is through drinking untreated or unfiltered water, while hiking, camping, or even accidentally swallowing a bit of water while swimming. Giardia is present in many waterways and it should be assumed that all water is contaminated and needs to be treated. Coldwater from the mountain stream looks enticing but don’t fall for it. Symptoms may take 1 to 2 weeks to develop but may continue to 6 weeks leading to diarrhea, stomach cramps, nausea, or vomiting, flatulence, and greasy stools. Ensure that water is free of Giardia parasites by using one of these 3 methods
Filter the water with less than one-micron pore size filter.
Boiling water for at least 1 minute at a full boil.
Treating it with chlorine or iodine according to directions.
Gross intestinal lesions are seldom evident, Giardia causes an increase in the epithelial permeability and an increase in the number and activation of T lymphocytes in the gut. This leads to a shortening of the brush border microvilli and causes reduced absorption of water, electrolytes, and nutrients. Together with decreased activity of the small intestinal brush border enzyme, the host suffers from malabsorptive diarrhea and malnutrition. Reduced activity of lipase and increased production of mucin leads to steatorrhea and mucus diarrhea. Clinical signs are often normal, however, Giardia infections in small animals may manifest as chronic weight loss and chronic or intermittent diarrhea particularly in the young. Feces appear soft, pale, malodorous and contain mucus and fat. Watery diarrhea is unusual and fecal blood is usually not observed, however, an animal may vomit. Differential diagnosis includes virtually all other causes of malabsorption and maldigestion such as exocrine pancreatic insufficiency.
Young remanence giardiasis can result in diarrhea, unresponsive to antibiotics, or coccidia stats. It should be suspected when feces are mucoid and pasty and animals less than 6 months of age show reduced weight gain. Giardia diagnosis involves a saline smear of feces that may show model oval trophozoites, unlike yeast or trichomoniasis they have a double nucleus. Fecal cysts 9 to 15 by 7 to 10 microns can be concentrated by the centrifugation floatation technique using zinc sulfate. Identification can be facilitated by iodine staining, because of intermittent excretion 3 fecal examinations should be performed over a period of 3 to 5 days. Specific detection can be enhanced immunofluorescence and commercially licensed techniques optimized for the species of interest. There are no FDA approved drugs for the treatment of giardiasis for dogs and cats. However, fenbendazole has been approved for use in Europe and is used off-label in the US. It has been shown to be safe in pregnant and lactating animals. A praziquantel parental and for battle, the combination has been used for 3 days. Extra label use of metronidazole for 5 days is effective in eliminating Giardia species from about 2 out of 3 infected dogs, but may be associated with the violation and neurological side effects.
Combination or sequential strategies, be sure to bathe the animals to remove cysts have also been tried. Currently, no drug is FDA approved for the treatment of Giardia in ruminants. So off label users would consult with the food animal residue avoidance database for guidance on withdrawal time fenbendazole and albendazole significantly reduce cysts excretion and clinical improvement in calves. Paromomycin for 5 days is also found to be highly efficacious in calves. For production animals and group house domestic animal management is the key to the control of Giardia. Cysts can cause infection and reinfection particularly if housing is crowded. Giardia cysts get infected immediately when they are passed in the feces and survive in the environment. Cysts are said to be a source of infection and also reinfection in the case of animals particularly those in crowded conditions. Feces should be removed from the environment daily, dogs and cats should bathe to remove cysts from the hair coat.
Disinfection with quaternary ammonium and steam or boiling water can inactivate cysts in the environment. To facilitate efficacy solutions should be left greater than 5 minutes before rinsing. Yards and animal runs cannot be disinfected and should be considered contaminated for at least a month after the removal of the last infected animal. Cysts may be inactivated by allowing the surface to dry thoroughly after cleaning. In summary, Giardia is a protozoan seen worldwide that causes chronic intestinal infection in most mammals, many birds, and people. Infection is common in dogs, cats, ruminants, and pigs. The highest rates of infection are seen in young animals. Affected domestic animals can be treated with antiprotozoal agents often in combination, but proper hygiene constitutes the best approach to animals in group housing.
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Giardia Life Cycle
The cysts are said to be more resistant forms and are responsible for the transmission of giardiasis. Both cysts and trophozoites can be found in the feces at the diagnostic stages. The giardia life cycle is as follows
Giardia cysts are said to be the infective stage of G. intestinalis. Only as few as 10 cysts will be able to cause infection. These types of cysts are typically ingested by the consumption of contaminated food or water or fecal-orally. They are capable of surviving outside of the body for a period of several months, and they are also relatively resistant to chlorination, UV exposure, and even freezing. The cysts are resistant forms and can survive for several months even in the cold water. Infection can occur by the ingestion of cysts which is present in the contaminated water, the food, or by the fecal-oral route through the hands or fomites.
The time when cysts are ingested, the low pH of the stomach acid will be producing excystation, in which we see the activated flagella will break through the cyst wall. This will usually occur in the small intestine, specifically at the duodenum. Excystation will release the trophozoites, with each cyst producing at least two trophozoites.
Now within the small intestine, the trophozoites will reproduce asexually and will be multiplied by the longitudinal binary fission, now remaining in the lumen of proximal small bowel where either they will float free or will become attached to the mucosa of the lumen.
Some of the trophozoites will then encyst in the small intestine. Encystation tends to occur most likely as a result of exposure to bile salts and fatty acids, and also a more alkaline environment. Encystation which usually occurs as the parasites transit toward the colon. The cyst then which is found at is the stage found most commonly in non-diarrheal feces
Both the cysts and trophozoites will be then passed in the feces, and are very infectious immediately or it will be shortly afterward. There is also the possibility of person-to-person transmission. Giardia can also infect the animals, and the beavers have been widely associated with the giardia outbreaks, although it is not definitively and their importance as a reservoir is unclear.
Clinical Features
The clinical features of Giardia include the below
The incubation period of Giardia infection varies from 1 week to 3 weeks.
The majority of the infections there go unnoticed, that is they remain asymptomatic.
Children are the ones who are most commonly affected, their ratio is about 40 to 80 %.
They suffer from acute Giardia infection or chronic Giardia infection.
Acute infections are associated with watery diarrhea, abdominal cramps, bloating, and flatulence.
An acute episode of Giardia may last for 5 to 7 days, it can resolve on its own or it can go to a chronic stage.
The chronic Giardia is associated with chronic diarrhea with malabsorption of the fat, vitamin A, proteins, and carbohydrates.
There will be weight loss, malaise, nausea, and anorexia.
The complication of chronic Giardia is the growth retardation and weight loss.
There can be delayed milestones in younger children.
FAQs on Giardia Life Cycle
1. What is the basic life cycle of the Giardia parasite?
The life cycle of Giardia involves two main stages. It begins when a host ingests the dormant cyst form, usually through contaminated water or food. In the small intestine, the cyst transforms into the active, feeding trophozoite stage. These trophozoites multiply and eventually form new cysts, which are passed out of the body in faeces, ready to infect a new host.
2. What is the difference between the trophozoite and cyst forms of Giardia?
The two forms of Giardia serve different purposes in its life cycle:
- Trophozoite: This is the active, pear-shaped form that lives and multiplies inside the host's intestine. It has flagella for movement and attaches to the intestinal wall to feed. However, it cannot survive for long outside the body.
- Cyst: This is the dormant, oval-shaped infective stage. It has a tough protective wall that allows it to survive in the environment (e.g., in water or soil) for weeks or months until it is ingested by a new host.
3. How does a person typically get infected with Giardia?
Infection, known as giardiasis, most commonly occurs through the fecal-oral route. This usually happens by drinking water or eating food that has been contaminated with Giardia cysts from the faeces of an infected person or animal. It can also spread through direct person-to-person contact, especially in settings with poor hygiene.
4. What are the main symptoms of giardiasis, the disease caused by Giardia?
The most common symptoms of giardiasis include diarrhoea, stomach cramps, bloating, gas, nausea, and dehydration. The infection can also interfere with nutrient absorption, leading to weight loss and greasy stools. Some people may be infected and show no symptoms but can still pass the parasite to others.
5. How is the Giardia parasite scientifically classified?
The systematic classification of Giardia lamblia helps place it within the biological kingdom. Its classification is as follows:
- Kingdom: Protista
- Sub-kingdom: Protozoa
- Phylum: Sarcomastigophora
- Class: Kinetoplastida
- Order: Diplomonadida
6. Why is the Giardia cyst so effective at causing infection?
The Giardia cyst's effectiveness comes from its remarkable resilience. It is protected by a tough outer wall that makes it resistant to environmental pressures and even to standard water disinfection methods like chlorination. This durability allows it to survive for long periods in water and soil, waiting to be ingested by a suitable host.
7. How exactly does the Giardia parasite cause diarrhoea and other intestinal problems?
The active trophozoites attach themselves to the lining of the small intestine using a special sucking disc. This large-scale attachment creates a physical barrier on the intestinal surface, which disrupts the body's ability to absorb fats and other nutrients from food. This malabsorption is a primary cause of the characteristic watery diarrhoea, gas, and greasy stools seen in giardiasis.
8. What happens inside the body right after someone swallows Giardia cysts?
Once swallowed, the tough cysts survive the acidic environment of the stomach. When they reach the small intestine, the change in environment triggers a process called excystation, where each cyst releases two active trophozoites. These trophozoites then begin to feed and multiply. As they travel down the digestive tract into the colon, they undergo encystation, forming new, hardy cysts that are then passed in the stool.
9. Can you get Giardia from your pet dog or cat?
While both humans and animals like dogs and cats can get giardiasis, the risk of getting it from your pet is relatively low. This is because there are different genetic groups (called assemblages) of Giardia. Humans are most commonly infected by assemblages A and B, while dogs are usually infected by C and D. Although cross-infection is possible, human infections are most often traced back to human sources of contamination.
10. Why are Giardia infections more common in certain settings like daycare centres or among hikers?
These settings have conditions that favour the transmission of the parasite. In daycare centres, close person-to-person contact and developing hygiene habits in children make it easy for cysts to spread. For hikers and campers, the risk comes from drinking untreated water from streams or lakes that may be contaminated with cysts from wildlife or human waste.
