Saturday, March 21, 2015

Taenia solium and the leaky brain cyst

For my other blog (warning: not a scientific blog), I wrote a little thing about why Spring is one of my favorite seasons (I mean, second to Autumn of course!) because it brings an abundance of cute baby animals to the world. One of my absolute favorites is the pig! Domesticated, wild, big, small, it doesn't matter.

Image from Daily Mail.
So, in honor of all the piglets being born this season, let's talk about a classic parasite with some new research twists. Taenia solium is a type of tapeworm that is specifically linked to pigs. T. solium is related to the "beef tapeworm of man" (Taenia saginatum, tapeworm associated with cows), but can cause some much more severe symptoms.

T. saginatum scolex imaged using electron microscopy. Image taken from the internet.
T. saginatum, the beef worm, is what everyone thinks of when they think "tapeworm": adult worms have a head, neck, and proglottids, and causes intestinal obstruction and discomfort. Oh, and it can live inside of you for up to 25 years!

In order to get your own tapeworm infection, all you have to do is consume poorly cooked beef which contains T. saginatum eggs. When the eggs "hatch", oncospheres (infective larva) migrate to the small intestine, where they will take 3 months to mature into an adult worm. Adult worms are typically 2 to 10 meters in length. Usually only one worm is found, unless you've consumed a heavily contaminated piece of meat or ate fecal matter that's full of gravid proglottids (the end pieces of the tapeworm). Fun fact: eggs can survive for months once they've left the body. Beware of old poop!

Taeniasis life cycle for T. saginatum and T. solium, via the CDC

Patients infected with a beef tapeworm (clinically described as "Taeniasis") may complain of non-specific abdominal symptoms, such as nausea, general pain and discomfort, or weight fluctuations. I say weight fluctuations because most people experience extreme weight loss (often misdiagnosed as anorexia), especially those affected in developing countries (where these parasites are most prevalent), but there have been a number of people who have infected themselves, by choice, and have reported it being "no big deal" or that they gained weight (see my favorite example: Michael Mosley of the BBC News). So, while most people experience weight loss, I suppose you could say that depends on your socioeconomic status, and whether or not you've had a choice to become infected.

T. solium life cycle from the Food and Agriculture Organization of the United Nations (fao.org)
T. solium can also cause all the same intestinal symptoms, and can live out a life cycle similar to that of T. saginatum. But, in some cases, T. solium can cause something called Neurocysticercosis (cue scary music). T. solium's life cycle and pathophysiology usually looks very similar to that of T. saginatum, only with smaller worms (4-7 meters in length). Neurocysticercosis occurs when you've ingested the eggs directly, such as ingesting contaminated feces. This happens to pigs when their food is contaminated with human feces (pretty ironic, right?).

T. solium scolex. Image from UNAM.
The consumed eggs hatch in the small intestines and the oncospheres are released. Oncospheres penetrate the intestinal mucosa and make their way to the blood. Once in the blood, they travel throughout the body and migrate to different tissues, where they will mature into cysticeri. The cysticeri really like skeletal and cardiac muscle, subcutaneous tissue, and lungs, but they can also get lodged in the central nervous system (CNS), including the brain and the cerebral ventricles. Once the cysticeri have chosen a tissue which to lodge themselves, they become calcified granulomas.


T. solium adhering to the epithelial cells of the intestine. Image from UNAM.
The most common location for cysticercosis to occur is the cerebral hemispheres, at the gray-white matter junction, but they can also be found in the cerebellum, the brainstem, the subarachnoid space, the basal cisterns, and the spine.

T. solium cysts in a human brain. Image from Discover Magazine.
 Obviously, having a 1-2 cm cyst calcifying in your brain will cause some damage. Neurocysticercosis is one of the leading causes of epilepsy in developing countries. It can also cause severe headaches, hydrocephaly and eosinophilic meningitis.

The National Institute of Allergy and Infectious Disease (NIAID) just released an article about the treatment-induced inflammatory response in pigs with neurocysticercosis. The current treatment of Praziquantel is apparently causing inflammation, blood vessel leakage, and damage to the blood-brain barrier. This means that new drugs need to be developed that can reduce inflammation at the site of the cyst(s) while maintaining the integrity and functionality of the blood-brain barrier and blood vessels.

Photo of the surface of the brain of a pig treated with the antiparasitic drug praziquantel showing blue-dyed (blue arrows) and clear (white arrows) cysts. The blue dye indicates disruptions in the blood-brain barrier. Image from NIAID/
Dr. Cristina Guerra-Giraldez.
This research only focuses on pig subjects, and has not yet been performed on humans infected with neurocysticercosis.


Want to avoid tapeworms and neurocysticercosis? The best way to do that is either to avoid eating meat, or to make sure your meat is cooked properly. Cooking meat properly is the best way to inactivate or kill most infectious diseases associated with meat consumption.

One of the major reasons diseases are so rampant in livestock is because a lot of treatments (mainly antibiotics) are used as prophylactics instead of at the onset of infection and symptom presentation. Animals that are raised in small, confined areas are more likely to be exposed to illnesses. When you are raising animals on a large scale and rely on them for income (whether through livestock trade, meat or dairy production), it can be really scary when one of your animals gets an infection, because you risk losing some of your income. It's obviously unethical to sell/trade sick animals, but it happens all the time, and is one of the main causes for the spread of disease to other regions. When prophylactic treatments are used, resistant infections are more likely to occur, which is an even larger problem (as I'm sure you can imagine).

Even if the meat you consume came from a healthy cow/pig/lamb/goat/chicken/turkey/etc., it might have been slaughtered in the same environment as a sick animal, which still puts you at risk. So, if you have a tendency to order your meat "rare", be sure you know the risks associated with that choice.

Edited to add:
I want to be clear that, even though I'm vegan, I believe choosing to be vegan is a very personal choice and no one should ever be bullied in to it. But, I also feel the need to add some information about the environmental impacts of eating meat to this post, since we are talking about risks associated with consuming meat. Considering the risks to yourself is very important, so you can actively minimize your risk of getting an infection or other serious health disparity (mostly through the long-term, excessive meat consumption),  but considering the long-term risks for the environment (ie- everyone on earth) is also really important. Here are some articles that you might want to consider reading before making a definitive decision about your dietary habits:

The Triple Whopper Environmental Impact of Global Meat Production: TIME

How does meat in the diet take an environmental toll?: Scientific American

Giving up beef will reduce carbon footprint more than cars, says expert: The Guardian

2500 gallons all wet?: EarthSave


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