Thursday, December 13, 2012

A Crappy Parasite

by Anuj Saluja

I love Jurassic Park. If you haven’t seen it[1] or need a refresher, here is the synopsis: a rich old man makes a park with living, breathing dinosaurs. Several experts and the old man’s grandkids come for a test visit. Naturally, [crap] hits the fan and the dinosaurs start wreaking havoc. When I was a kid, it was terrifying because of the velociraptors and T-Rex chasing the hapless humans. It still scares me as an adult but for a whole different reason. I was watching it recently and one scene had me screaming at my tv. No, not the kitchen raptor scene[2] but rather a much more subtle scene: Dr. Grant, the protagonist of the film, washing and drinking from a fresh water stream. As a microbiology major, this made me cringe – hasn’t Dr. Grant heard of Giardia lamblia?! Running from velociraptors is pretty bad, but running after being infected with G. lamblia cysts? Well, consider yourself literally [crap] out of luck.

Figure 1 – A Giemsa stain of G. lamblia.

Giemsa helps visualize chromosomes.

Here you can see the two nuclei of

G lamblia as well as another organelle

across the middle. 
Most campers are familiar with G. lamblia; the parasitic protozoon is the most common cause of epidemic waterborne diarrheal disease (Giardiasis). This usually happens because of fecal contamination of water. The parasite was first discovered by an ambitious Antony van Leeuwenhoek when he decided to check out his diarrheic feces. From afar, the protozoon looks similar to other human parasites, which often leads to misdiagnosis (2). However, upon closer scrutiny, it has several characteristic features that can distinguish it from other members of the same family, Hexamitdae. They are flagellated (meaning they are mobile organisms) and have a unique structure: they have paired organelles, including two active nuclei, as well as an attachment organelle known as the ventral disc. (2). Another distinguishing feature of G. lamblia is its characteristic “smiley face”[3] when stained (see figure 1). Potential hosts for the parasite include a variety of animals aside from humans. This includes cats and dogs as well as beavers (hence Giardiasis known colloquially as “beaver fever”) (1)

G. lamblia begins as a cyst (a dormant or non-active cell) that has been excreted with the feces of an infected individual. When the cyst is ingested by a host, a trophozoite (a young, active cell essentially) emerges. It is motile and absorbs nutrients from the host’s small intestine, causing dehydration and diarrhea. During this stage, the parasite replicates through binary fission, meaning new daughter cells are genetically identical to mother cells. Eventually, they too become cysts and are excreted out of the system (some trophozoites are excreted out too but do not survive – only cysts can survive outside the host) (2).  The cysts are tough buggers – they can survive pretty extreme environmental pressures like fluctuating climate and most predators - they’ll just infect them and multiply.

G. lamblia cysts have also been found in pools (3). In 1988, several swimmers contracted Giardiasis after swimming in a public pool. Cysts are normally quite chlorine resistant. According to a formula provided by the paper, a pool must have .3 mg of chlorine for 50 minutes if it is at 25 degrees Celsius in order to kill any cysts (3). On the day of occurrence, a handicapped child who happened to be infected with the parasite had, let us say, “an accident” in the pool. By an inconvenient coincidence, the pool’s chlorine tank ran out, which led to a small outbreak of Giardiasis. Ultimately, this may have been due to bad luck. However, a slightly more alarming publication was released by the CDC in 2008 (4). In it, they describe several instances where cysts of the similar species, Giardia intestinalis, were found in several chlorinated pools in Atlanta. The authors note that even though the cysts were taken from a small sample size, the findings were statistically significant. Given the similarity between the two species, it would not be too surprising to see cases of Giardiasis from G. lamblia popping up from folks at swimming pools. If you own one, it’s probably a good idea to make sure no vermin have “an accident” and to make sure your chlorine levels are up to par.

In general if you live in a modern country, unless you are out in the middle of nowhere camping, you are fine – your home tap water doesn’t have any G. lamblia. Yes those two reports from the pools are from first world countries but they are rare instances (the papers even note that the sample size is small). However, for poor third world countries, G. lamblia is a real threat. Most don’t have proper water filtering systems, meaning most of their water is highly susceptible to contamination.

If I may get serious for a moment, Giardiasis can do some serious damage for poorer populations; severe diarrhea can lead to dehydration which is life threatening in a poorer country without available healthcare (5). That said though, treatment for Giardiasis is simple. Metronidazole, an antiprotozoal is used to combat Giardiasis and clears it up quickly. More powerful antiprotozoals can also be used if metronidazole fails (2).

Now back to Dr. Grant from Jurassic Park and his callous[1] use of the stream water. Instead of directly applying the water, he could have boiled it. However, it’s the 21st century and the movie is 20 years old. We are in the smartphone era now[2]! Surely there must be some high tech method of cleaning up G. lamblia cysts from water.

Indeed it does – it’s this brilliant device called the sun. Solar Disinfection or SODIS is used to kill pathogenic microbes in drinking water. The best part is that it is simple and cheap – just use a transparent container like a plastic bag, water bottle or glass bottle and place it in direct sunlight for about 8 hours. The UV light of the sunlight will damage the cysts generally.  The sunlight also stimulates the microbes that perform aerobic (oxygen required) photosynthesis and release O2 gas into the water.  The gas is highly reactive and can disinfect any remaining microbes (6). This has resulted in a reduction, especially with children, of diarrhea from drinking water.

Using Giardia muris instead of G. lamblia, a research group successfully showed that SODIS can work for killing cysts in water. They did this by setting up suspensions of G. muris cysts and exposing them to various conditions of light. They then exposed mice to the cysts and found that cysts that were subjected to full SODIS conditions (40 degrees Celsius and 870 W/m2 light, 4 hours) rendered completely un-infectious. Granted, this is tough to achieve on a smaller scale – like say a camping trip unless it’s sunny and hot, the authors suggest that in emergency scenarios – like say a bad hurricane, SODIS can be used to clean up water from G. lamblia cysts[3].

Even though it’s treatable, Giardia lamblia is not a microbe to be trifled with. Giardiasis is not pleasant and can cause some serious dehydration. If you camp regularly, be sure to take the proper precautions to prevent infection. This includes using clean water to clean any dishes you have. Plastic water bottles with filtering devices have recently become commercially available. Take full advantage of them – they usually say how powerful they are on the label and Giardia species are often listed amongst the list of screened microbes.

  1. Willey, Sherwood, Woolverton. Prescott’s Microbiology: 8th Edition. McGraw Hill, 2011. New York, NY. Pg 584 – 586, 730
  2. Ortega-Pierres et al. Giardia: A Model Organism online textbook. 1st Edition, 2011 SpringerWien New York.
  3. Porter, et al. Giardia Transmission in a Swimming Pool. American Journal of Public Health. June 1988. Vol 78 no 6 pg 659 – 662.
  4. Shields, et al. Prevalence of Cryptosporidium spp. and Giardia intestinalis in Swimming Pools, Atlanta, Georgia. Emerg Infect Dis. 2008 June; 14(6): 948–950.
  5. Dewey, Daniel MD. World Altering Medicine: Breath of Life. Lecture. University of Minnesota. December 2010.
  6. McGuigan et al. Batch solar disinfection inactivates oocysts of Cryptosporidium parvum and cysts of Giardia muris in drinking water. Journal of Applied Microbiology ISSN 1364-5072. J Appl Microbiol. 2006 Aug;101(2):453-63.

[1] I of course realize that it’s Hollywood and worse sins have been committed in films. Also, stopping to sterilize water is probably the last thing on your mind when you are being chased by ravenous dinosaurs
[2] Smokey the Bear and PETA may have heart attack because of him starting a fire on an  animal reserve too
[3] While they didn’t use G. lamblia, G. muris acted as a model and the group notes that this can be applied to G. lamblia

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