Saturday, December 21, 2013

Here's Lookin' at You, Giardia

Oh, Hi!
Arguably one of the most adorable of the diarrhea-causing protozoans would have to be members of Giardia. Sure, they cause terrible fatty stools, intestinal pain, and dehydration, but hey, at least it looks cute while doing it. I used to think that this parasite caused bloody stools, but I recently learned that this is not the case with Giardia. Rather, stools become "fatty". You see, as these parasites feed on mucous secretions within the intestinal walls of their hosts, they cause considerable damage to the microvilli and make it difficult for the intestine to absorb fats and other nutrients. This causes diarrhea and the aforementioned "fatty" stools. This parasite has been infecting humans for many, many years. Not many years ago we discovered that Giardia played a role in causing much of the dysentery contracted by the Crusaders in the 12th and 13th centuries as they invaded Palestine. The parasite didn't make its
grand appearance onto the world stage  until 1681, when Van Leeuwenhoek saw it for the first time. He found it as he examined his own stool during a bout of diarrhea exclaiming:

"My excrement being so thin, I was at divers times persuaded to examine it; and each time I kept in mind what food I had eaten, and what drink I had drunk, and what I found afterwards. I have sometimes seen animalcules a-moving very prettily..."

But I suppose I'm getting a bit ahead of myself. Let's start with the basics.

As with any discussion of protozoan systematics, please keep in mind that as researchers discover more about these creatures their taxonomic categorizations tend to change. It is likely that even the upper taxonomy I am about to describe has since changed and I myself could easily be behind the times as I don't study this parasite exclusively and am not familiar with the latest taxonomic literature regarding this group of organisms. Like many other things, protozoan taxonomy exists in a state of perpetual flux. Disclaimers aside, this group belongs to Phylum Retortamonada as it lacks both dictyosomes and mitochondria. Members of this group are all flagellated and are either intestinal parasites or live freely in anoxic kinds of environments. They further belong to Class Diplomonadea and to Order Diplomonadida. Members of this order have two karyomastigonts (nuclei and associated organelles) and twofold rotational symmetry. Giardia further belongs to the Family Hexamitidae for having two equally-sized nuclei arranged beside one another. This morphological feature gives them that endearing "looking at you" feature that's made them so famous.

Interestingly, there have been more than 40 species described from this genus, but many of these have now been rendered invalid with the advent of molecular biology. Today, only five species are considered valid species within this genus. Two species within this genus infect birds, one infects amphibians, and two infect mammals. Of those two, only one causes disease in humans: G. duodenalis (formerly known as both G. intestinalis and G. lamblia).

From an evolutionary standpoint, Giardia duodenalis is interesting to study. It's simplistic life and primitive  morphology tells us that it is among the oldest of the protozoans. These guys are a basal group of protozoans existing before the development of mitochondria found in other protist groups. They also possess many flagella, which is also thought to be an ancestral condition.

Life Cycle
The life cycle of this parasite is simple. Fecal-oral contamination. Something that is infected poops in a place where the parasites won't dry out. At this point the parasites are in a cyst stage of their life cycle. When someone eats food that has been accidentally contaminated or drinks from a Giardia-rich water source, they pick up these cysts. Once in the body, the cysts transform into feeding stages known as "trophozoites". Trophozoites attach onto host intestinal tissues and feed off of the mucous linings causing all sorts of problems as it does so.

Giardiasis (a.k.a. "Beaver Fever" or "Recreational Water Illness")
We are just hangin' out...
munchin' on some mucous, yo!
Infection with this parasite is highly contagious. It spreads rapidly in areas where sanitation is not G. duodenalis either. These parasites can be passed by dogs, cats, sheep, and even beavers (hence the first common name for the disease).  Infections are easily acquired from water parks, lakes, and even resorts (hence the second common name). It can also be contracted from unwashed fruits and vegetables, or from contaminated drinking water.

Much of the time, cases of giardiasis are so mild that they show no clinical symptoms. However, some cases include symptoms like incapacitating diarrhea, intestinal pain, weight loss, flatulence, dehydration, and excess mucous production. In severe cases, patients present with colic or jaundice caused by infections of the gallbladder. Because the parasites disrupt fat and nutrient absorption, dietary diseases can also be come an issue if left untreated long enough. There are very few fatalities, but the disease is certainly no picnic.

Most of the time giardiasis can be confirmed by examining a stool sample for cysts and trophozoites. Immunological techniques are also useful today. Things like ELISA testing or the use of PCR have been helpful in diagnosing giardiasis. In rare cases, duodenal aspiration is required to demonstrate these life stages if a person is not regularly passing the parasites. Now, I had never heard of duodenal aspiration, but it sounded like it wouldn't be much fun. Looking it up confirmed my suspicions. This involves passing a tube orally into the duodenum (part of the small intestine) and aspirating to dislodge the parasites for a proper sample. Nope. Not fun at all. Then again I don't know if that would be worse than the alternative, which would be an intestinal biopsy. Pick your poison.

Lucky for us, being diagnosed is more difficult than determining how to treat a person with giardiasis. Metronidazole and quinacrine are the two drugs most often chosen to combat infection. This completely cures the patient in only a few short days. Because it is highly contagious, it is good practice to dose all immediate family members/roommates as well to avoid reinfection. It is equally good practice to determine the source of infection to take the measures needed to prevent future infections.

Seriously, even with all the symptoms, you have to admit these are adorable little guys!

A Colorful History
I want one!
(The plush, obviously.
Not the actual parasite
despite its cuteness.)
After appearing on Leeuwenkoek's microscope stage in 1681, this parasite went on to  pop up in many places around the world. Giardiasis outbreaks have occurred in many countries with a variety of impacts, ranging from small, localized epidemics to large-scale contamination of major city water supplies. As archaeoparasitology extends its reach into the realm of molecular biology, ELISA and other techniques are being utilized to reveal more about the effects of these parasites in both historic and prehistoric human populations. As mentioned earlier, a 2008 study pegged this parasite as part of the reason that Crusaders suffered from dysentery. How cool is that?! Other studies have revealed Giardia's presence in places far away, such as ancient Peru, as well as in places closer to home, such as a cemetery in Kansas dating from 1860 to 1900.

Moral of the Story
These ancient parasites are beginning to reveal to us more about the daily lives of people in both ancient and historic times the world over. They are teaching us that our ancestors suffered from some of the same things we struggle to combat even today despite our vast improvements in sanitation. Once again, here is a parasite to be be marveled at for its ability to survive this long as a species without something as fundamental as mitochondria. It's an easy parasite to doesn't typically cause much more than discomfort, it's easy to treat, and let's face it, its morphology makes it kind of cute. (Plus you are very unlikely to die from it unless you refuse to get yourself treated.) Here's lookin' at you, Giardia.

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