Giardia: an infective cause for stomach bloating

So this is bit of an odd topic but does feature in an interesting piece of medical history so I thought it worth talking about.  Giardia belongs to a

A. Van Leeuwenhoek

class of organisms  called protozoans.  These animals are so small they required the invention of the microscope to be identified.   One of the reasons postulated for this invention was Antonie van Leeuwenhoeks own dysentry – the man was so distressed by his symptoms he in vented the microscope to figure out what was causing them!!   There is a question mark over whether he linked the new organism he identified as being causative of gastrointestinal discomfort however inventing the microscope for whatever reason has clearly been a game changer for for microbiology!  Work life balance 17th century style; sound like it was similar to 2018.

It was not until 1954 that there was a complete link established between Giardia and the illness we accept it causes today.

Giardia lamblia Trophozoite Licence

Giardia lamblis, also known as Giardia duodenal or Giardia intestinalis, is a very common intestinal pathogen with an estimated half a million new cases being identified worldwide each year.   This is a bug known as a flagellated protozoan and while microscopic it is larger than bacteria and viruses.  Giardia are  a single celled parasitic organisms living in the guts of animals, be they other humans, cats, dogs, livestock and even beavers.

Transmission occurs when an infective giardia cyst is swallowed by an animal or human, this cyst having been shed in the feaces of another infected animal or human.  Most commonly the contaminated poo finds its way  into a water source such as a creek, water tank or a pool, if this water source is used for drinking, incidentally or on purpose, the infection can spread from animals to humans.  Whilst I would not have volunteered for the study, scientists have established that for a human to become infected they need to ingest ten or more cysts, and this is known as the infectious dose.  The acidic environment of the persons stomach then causes the cyst to hatch.  The organism that hatches out of the cyst is known as a trophozoite and it attaches itself to the wall of the small bowel and can ultimately grow, reproduce and the local population of giardia increases.  The giardia then expands into the large intestine where they form more cysts as part of their reproductive cycle.  These cysts pass out in the stools which in turn contaminate the environment once again.

The giardia cysts can last in the environment for between 28 to 84 days while remaining infective.  A watery environment increases their chance of survival and the ability to infect a new host.

As an interesting side note I have learnt from veterinary friends in America that Giardiasis is known colloquially in North America as ‘Beaver Fever‘.  This name was established after a bunch of hikers in Banff National Park got sick after drinking water from a stream where beavers lived.  However all sorts of animals can carry this organism be they cats, dogs, monkeys, cows, sheep, rats, ferrets, birds and horses.  As you can see contaminated rain water tanks are often a source of infection.

Stool Sample

So how does this microscopic organism cause trouble?  There is a complex interplay between you and your parasitic organism.  When the organism attaches itself to the lining of the small bowel they cause firstly inflammation and then weakening and thinning of the lining the bowel.  As the population of giardia in the bowel increases so does this process.  This atrophy makes the bowel less effective at breaking down and absorbing food.  As such the food remains undigested and ferments in the bowel rather than being digested – causing a majority of the symptoms associated with giardiasis.  Mild symptoms include a grumbling nausea, diarrhoea and weight loss.  In more heavy infestations patients will report symptoms of flatulence, bloating diarrhoea and significant stomach pain.  Sometimes patients may experience burping that creates an ‘eggy’ smell.  Another common experience for those infected with giardia is that they experience diarrhoea that is worse after eating food containing lactose e.g. milk, whey protein, cheese, this is thought to be due to the lack of digestion and consequent fermentation that occurs by bacterial in the large bowel.  Due to the indigested food passing through the digestive system patients may notice large bulky foul smelling poos that are difficult to flush.

In extreme cases patients may suffer from a chronic ongoing disease with very little response to treatment.  Luckily however this is the exception rather than the rule and most people notice mild to moderate symptoms that resolve well with appropriate treatment.  There has been a suggestion that chronic infection can lead to other pathologies such as arthritis, irritable bowel syndrome, food allergies and even chronic fatigue syndrome however research in these areas is not high quality and the links are somewhat tenuous.

Diagnosis of Giardia can often be difficult.  A poo sample either looking for giardia cysts or parasites, or a test trying to detect the DNA of these organisms in a patients poo can often assist in identify the problems.  Cysts aren’t shed consistently however so several samples may need to be taken over a month or so in the hope of identifying the cause of infection.  If these tests are negative but the doctor still suspects a giardia infection then they may refer for endoscopy.  During this procedure a small camera is passed into the small bowel to assess for inflammation and samples can also be taken to look for the organism.  As a result of this, the diagnosis of giardia can often take a while, so if you or your doctor suspects a giardia infection it’s important to work together to make the diagnosis despite the frustration that “negative” results may cause.

The good news is that once identified treatment for giardiasis is relatively easy.  It is estimated that up to 90% of cases are easily cured with a 2 week course of antibiotics.  Due to the highly infective nature of the organism it is important to consider other family members health if one person in the family has a positive result.  Often your doctor may elect to treat the whole family in this situation.  It is also important to identify and treat potential sources of infection, such as that rain water tank!

How do you avoid catching giardia? Anyone with giardia needs to stay home for 48 hours following completion of treatment.  If there has been an outbreak of this infection then making sure stool samples are clear following treatment may be necessary.  Prevention may involve avoiding potentially contaminated water courses including pools and contaminated mains water sources.

And while we are treating the family, how does your pet avoid catching giardia?  Do not allow them to drink from outside water sources.  Try to walk your pet away from where other animals relieve themselves and always clean up after your animals.  Make sure there are not too many animals living together in very close proximity – everyone needs their space!  And if you are still worried consider getting a stool sample for your vet to analyse.

So if you are experiencing burping, bloating, weight loss or diarrhoea it’s important to see your GP as leaving giardia untreated can in some circumstances result in chronic disease like irritable bowel syndrome.

GPearls on the GC:

  • medical advancement sometimes come from the unlikeliest inspiration
  • faecal sampling is not the be all and end all of diagnosing giardia
  • diarrhoea, bloating after drinking milk could be giardia, not lactose intolerance



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