Giardiasis: Symptoms and Transmission

Giardiasis emerges as a result of Giardia lamblia, a microscopic, single-celled parasite that establishes itself in the intestines of both humans and animals.

Initial indicators of infection may encompass sensations of nausea, a decline in appetite, and discomfort in the upper intestine, coupled with an overall feeling of malaise, potentially accompanied by a mild fever and chills.

Following this, there is typically a sudden onset of explosive, watery diarrhea with an unpleasant odor, accompanied by increased flatulence and abdominal swelling. Additional acute symptoms include bloating, belching, cramping, and a reduced desire to eat; these manifestations typically appear 1 to 2 weeks after the ingestion of cysts. Individuals under stress or with weakened immune systems may experience more severe symptoms and a diminished ability to fend off the disorder.

The illness usually resolves on its own, lasting for a span of 2 to 6 weeks, but it may sporadically reoccur or progress into a chronic state. Nevertheless, not everyone who acquires the infection exhibits symptoms. Giardiasis is more prevalent in children, elderly individuals with compromised health, and those with dysgammaglobulinemias.
Giardiasis: Symptoms and Transmission

Giardiasis in children

Giardiasis is produced by unicellular parasites called Giardia lamblia that can be found all over the world, especially in areas of poor sanitation, unsafe water. The World Health Organization reported that 200 million people in Asia, Africa and Latin America have symptoms of giardiasis with some 500,000 new cases a year, especially among children.

Giardiasis has been reported to be associated with delayed growth in malnourished children under 5 living in low- and middle-income countries.

Infection with Giardia lamblia may manifest in a wide spectrum that includes asymptomatic carrier status, principally in adults, and acute and chronic diarrhea with or without evident signs of malabsorption, failure to thrive or lack of weight gain, mostly observed in children. Researchers have indicated that children with recurrent attacks of diarrheal episodes are susceptible to malnutrition.

A study conducted in Malawi among 6-to-18-month-old children reported association between asymptomatic giardia infection and growth retardation, particularly stunting. (Acta Paediatr. 2019, 108, 1833–1840)

Reported prevalence of giardiasis in Brazilian children vary from up to 14.6% among diarrhea cases within a specific population to 78.3% among day-care and school settings.
Giardiasis in children

Giardiasis: Cycle and mode of transmission

Giardia lamblia, once considered a harmless commensal organism, has become the most common pathogenic intestinal parasite in the United States. Children are at the most risk from the clinical consequences of Giardia infection, particularly those in developing countries and living in disadvantaged community settings.

Outbreaks of giardiasis linked to drinking water and food handlers [2] have been documented. Large, prolonged outbreaks linked to recreational water, particularly chlorinated sources, are less common.

Giardia exists in two forms: the trophozoite is responsible for clinical illness, and the cyst for transmission of infection. Transmission of G. lamblia is by the faecal–oral route, and can be person-to-person, animal-to-person, foodborne or waterborne. The infection is acquired by ingesting cysts, which are excreted in the feces. As few as 10-25 cysts are sufficient to establish an infection in some humans. Some livestock may be infected by as few as 1–10 cysts.

As trophozoites pass through the small intestine they encyst where the trophozoites then multiply. Many of the dividing trophozoites are carried toward the colon, and encyst along the way, in response to bile salts and other stimuli. Cysts can appear in the feces from 3 days to 3 weeks after infection, depending on the host species.

Excretion usually begins around the same time the first symptoms (if any) appear. Cysts voided in the feces are the infective stage and are immediately infective if ingested. The cysts may be transmitted directly from one individual to another under circumstances that are conducive to fecal-oral transfer such as in daycare centers or in environments where hygiene levels are compromised
Giardiasis: Cycle and mode of transmission

Genome of Highly Infectious Parasite, Giardia Lamblia Unlocked

Genome of Highly Infectious Parasite, Giardia Lamblia Unlocked
Giardia lamblia, one of the most common human parasites in the United States, causes more than 20,000 intestinal infections a year, often through contact with contaminated drinking or swimming water. In the September 28 issue of Science, an international team led by researchers at the MBL (Marine Biological Laboratory) describes the complete genome (genetic sequence) of Giardia, which could lead to the development of new drugs to combat this persistent infection, called giardiasis.

Even though there are treatments now available, a number of people get chronic giardiasis, which is difficult to eliminate. So there is interest in new treatments. The Giardia parasite lives in the human intestine in a swimming and feeding form called a trophozoite, which is eventually expelled through the stools. Outside the body, Giardia takes the form of a highly infectious cyst that can live for weeks in water, soil, food, or on other surfaces.

Giardiasis is most common among children, especially those who are exposed to diaper changing. Swimmers, hikers, campers and others who drink untreated water are also prone to the infection (hence the nickname "backpacker's disease" or "beaver fever"), as are international travelers. Common symptoms include diarrhea, nausea, stomach cramps and gas, and usually persist two to six weeks. Because the parasite clings to intestinal cells that absorb fats and nutrients, giardiasis can lead to severe complications such as poor nutrient absorption and weight loss.

Although not life threatening, Giardia is a rather fastidious parasite and quite important from an economical viewpoint worldwide and in the United States, where it constitutes a major cause of diarrheal disease in children in daycare centers. Analysis of the Giardia genome revealed several unusual proteins that are promising drug targets. Drugs can be devised that will interfere with the parasite's ability to replicate, or to move or bind in the small intestine, or to exist at all.

The MBL team also investigated the evolutionary history of this ancient parasite. Giardia is a single-celled eukaryote, meaning its cell has a nucleus, as do the cells of humans and most other multicellular organisms. But the Giardia genome is compact compared to other eukaryotes, with simplified machinery for several basic processes, such as DNA replication and RNA processing. If the Giardia genome had originally been complex and experienced gene loss over evolutionary time, Morrison says, one would expect to see parts of the machinery intact and parts missing. This, however, wasn't the case.
Researchers embarked upon this genome project because of its importance to human health and suggestions from earlier molecular analyses that Giardia represents a very early-diverging lineage in the evolutionary history of eukaryotes. Giardia's genome content and architecture support these theories about the parasite's ancestral character.

Another important finding is that the genes that allow Giardia to evade the human immune response are organized differently than in other parasites. In the host intestine, Giardia eludes an immune system attack by shifting the proteins it displays on its surfaces. The genes for these surface proteins are scattered throughout the Giardia genome rather than found in clusters, as in other parasites.
Genome of Highly Infectious Parasite, Giardia Lamblia Unlocked
Extract from: http://www.medicalnewstoday.com