Giardia lamblia, a parasite.
Giardia lamblia is a flagellated protozoan parasite such as you see on the image on the screen.
It is transmitted as are most other parasites by fecal-oral spread of the cysts via contaminated water.
Incubation once one ingests the cysts typically takes up to 14 days
but it can be almost quite immediate.
Diagnosis of Giardia is by demonstrating multinucleated cysts or the flagellated trophozoites in the stool.
We have a beautiful picture of a flagellated trophozoite
by scanning electro-microscopy on the right side of the slide.
Stool antigen however is the more common mechanism of making the diagnosis
and very reliable sensitive and specific antigen tests exists.
This is a complicated slide.
But let's look first at the processing of the cysts on the right side of the slide.
As with most other parasites, the initial step is to ingest a dormant cyst, a fully coated cyst
and then at some point, in this case in the proximal duodenum, the cyst excysts itself,
so it opens up to release the active trophozoites.
Then, while processing through the intestine, the trophozoite develops further maturation
and then ultimately encysts itself and is expelled in the feces.
It’s the process during this intestinal passage that disease can occur if entrance into
or through the intestinal mucosa also occurs.
So patients who are most susceptible then, looking at the slide bullet points on the left are -
the ones who are most susceptible are those with underlying gut abnormalities
or who actually have hypochlorhydria,
those who are immunodeficient especially those who have a low level of immunoglobulin A, the mucosal antibody.
Patients who are blood group A positive which is interesting
because it means they may express a specific binding site for the trophozoites to enter and cause disease.
Patients with malnutrition, possibly because they already have disordered gut integrity
but also possibly because they are already in the little point nutritionally
in any disease is sufficient for them to be negatively affected.
The cyst themselves are survivors, they resist heat and cold, they resist drying,
they even are able to co-infect with other organisms
so Giardia is absolutely a negative bad player in terms of parasitic disease.
Ultimately during that normal processing of the cyst through trophozoites back to cyst stage
the trophozoite might adhere to the villi of the intestinal epithelium
and then it releases proteinases which cause a physical injury at that site.
With physical injury comes reactive inflammation, reactive inflammation causes malabsorption,
so one gets in effect a malabsorptive diarrhea.
Clinical manifestation of Giardia, after that very short incubation period,
then one may have Giardia disease up to three weeks and it is very unpleasant.
The diarrhea, that malabsorptive diarrhea is of course very watery, very foul-smelling
because one is unable to process those fats and even sometimes the proteins
and so they all come out with secondary processing by normal bowel flora into a very foul-smelling mess.
Patients in addition will have nausea, anorexia, they’ll have diffuse abdominal cramps
and bloating; they will certainly have a high amount of flatulence
because, again, the normal flora bacteria have a lot of stuff to munch on
and that processing of the fats releases a lot of gas and then of course,
malabsorption has secondary affects for nutrition.
Treatment - metronidazole, not just an antibiotic which covers anaerobic bacteria
but also a very effective treatment for amoebic disease and parasitic disease
such as in this case the Giardia lamblia.
Secondarily, also tinidazole is also very effective amoebicidal drug
and both have great efficacy in this case.
So in general, Giardia lamblia is a significant pathogen in the world.
It is present in many of the world's water supply and even if one thinks one is safe
by living in a developed first world country, in fact, water supplies in wells
can be highly contaminated by simple seepage of fecal infested water.
So drink carefully out there and watch carefully for Giardia.