Sunday, August 31, 2014

Cordyceps Fungi: Bringers of Death, Givers of Life

Cordyceps sp. growing
from a lepidopteran
Today, I'm going to stretch your parasitophilia into a realm it has seldom explored. Today, we will look at a genus full of fungal parasites! First and foremost, if you don't know much about fungi, especially parasitic fungi, you should take some time to read up on them because they are really fascinating organisms. Like something straight out of science fiction, parasitic fungi are capable of everything from mind control to mummification. Such feats are unimaginable to the non-mycophiliac, but don't worry...I'll convert you! ;)

For this blogpost, we will look specifically at one of my favorite genera of parasitic fungi, the genus Cordyceps. The name for this genus comes Latin root words meaning "club" and "head", which relate to the characteristic shape of the fungi's fruiting bodies (i.e. "mushrooms"). Although Cordyceps spp. can be found in lots of places, the majority of species are described from Asia as the fungi prefer humid environments like tropical forests. There are approximately 400 species within this genus that can be found all over the world. All of these species (as far as I know) are parasitic. Most species parasitize insects or other arthropods, but some feed on other fungi. These fungi, like all fungi, produce mycelia (mats of fungal structures called "hyphae", which are kind of like super-awesome roots...they are used for nutrition absorption and help to anchor the fungi), however, unlike other fungi the mycelia from these fungi invade and eventually replace host tissues. The replacement of the host tissues with Cordyceps mycelia effectively mummifies the host and feeds the fungus in the process so that it can produce fruiting bodies, which will then produce reproductive spores by the thousands.

Look! A photo of a Cordyceps sp. taken at UNL!

Paras and Parasect
Cordyceps fungi have gained pop culture popularity for their creepiness. Even the gaming industry has picked up on how sci-fi-esque these little guys can be. For example, think back to your childhood and consider the Pokemon character, Paras. Paras starts as this crab-like creature with two mushrooms on its back. It evolves into Parasect once it reaches level 24. At this point, the fungus takes over the arthropod and the animal's eyes become milky-white in submission. The parasitic fungus induces the animals to live in caves and other dark, moist environments so that the fungus can grow. Swarms of Parasects can devour trees for nutrients. These have GOT to be inspired by Cordyceps, though I'm not aware of any directly-stated connections. Some games are less subtle; part of the plotline in the video game The Last of Us centered around a mutated strain of Cordyceps that turned people into zombie-like creatures. (Sounds right up my alley, huh?) Additionally, these fungi have made their way into some amazing artwork.

Poster from The Last of Us
featuring mutated Cordyceps.

A piece from DeviantArt
featuring a Cordyceps-like fungus.
Getting back to reality (oh, there goes gravity), a wide range of Asian cultures have utilized these kinds of fungi for traditional medicines. These have been used as aphrodisiacs, treatments for kidney and lung issues, and for revitalizing the fatigued elderly. Scientific researchers have even identified active compounds from these fungi that have pharmocological potential for treating cancer, liver disease, depression, and diabetes. (That's right, these things have hypoglycemic effects too...who knew?) In fact, a paper came out this past April that was titled: "Extract of Cordyceps militaris inhibits angiogenesis and suppresses tumor growth of human malignant melanoma cells". To translate for those of you struggling with the terminology, angiogenesis is the formation of blood vessels, which is necessary for tumor formation. This paper described how using an extract from the fungus not only slowed down angiogenesis, it also induced apoptosis (programmed cell death) in malignant melanoma cells (the bad, quickly-growing kind of melanoma). This study suggested the potential use of this fungus in the treatment of solid, cancerous tumors for its potent effectiveness. Aside from this, there have been a number of other studies looking to various Cordyceps species for their anti-cancer properties, but why stop there? It turns out that members of this genus also have anti-inflammatory properties, antioxidants, anti-fibrotic bioactivity, and even anti-trypanosomal activities! How awesome is that?!?!

The Moral of the Story
As most things in nature, Cordyceps has two sides...that of the villain and that of the hero. Their excitedly terrifying capabilities to suck their hosts dry to the point of becoming mummified cases of their former selves makes them the perfect organisms for science fiction stories. Their medicinal properties bring the potential for life and a sense of hope to those suffering from a wide variety of illnesses. Yes, the Cordyceps fungi exist as the duality of life and death, hope and despair, love and fear. It's a group of parasitic fungi worthy of reverence and deserving of our admiration.

Also, here's a link to a sweet Cordyceps video clip from the BBC narrated by none other than David Attenborough. Enjoy! :)
I'm not going to tell him....

Sunday, August 24, 2014

Ticks That Make You Sick: Ixodida-Induced Vegetarianism

Greetings fellow parasitophiles! I'm sorry that I've been out of the loop for so long. I have a million excuses for not writing...teaching, book publishing, revising to two different manuscripts for scientific publication, traveling to another country to work on an excavation site, moving into a new home, preparing for the fall semester...but none of these are good ones. As you can probably tell, life's been more than a little crazy for me this summer! All of my lame excuses aside, today I'm jumping back on the horse to blog about parasites. Let's start with something most of us have had to deal with at some point...ticks.

Between field work, camping, hiking, and lots of other types of outdoor activities, most people have encountered these little ectoparasites. These menacing little creatures strike fear, disgust, and anger into the hearts of all those who enjoy the great outdoors. A great variety of species exist, but only a handful carry diseases that we have to worry about. Rocky Mountain Spotted Fever, Lyme Disease, Ehrlichiosis, and others are problematic here in the states. It would be easy to pick one of these diseases to discuss at great length here on Parasitophilia, but I have something a little different in mind for today. Today, we won't talk about an infectious disease at all. Today, we will discuss something else that can come from being bitten by ticks....something I never thought could be associated with acquired food red meat.

I only just heard of this acquired allergy within the last few weeks, but the research goes back several years. The oldest paper that I could find on the subject (doing only a quick search, not an in-depth one) was published in 2009. This paper described 25 patients in New South Wales who developed allergies to red meat after suffering from reactions to local tick bites. The authors suggested what may have been the first documented association between tick bites and food sensitivities.

Fast-forward to a year ago (2013). A paper was released describing an oligosaccharide known as galactose-alpha-1,3-galactose (here-after referred to as "alpha-gal") having a connection to red meat allergy. You see, alpha-gal is only produced by non-primate mammals and by New World monkeys. Humans, other primates, and Old World monkeys produce an IgG antibody that works against alpha-gal. Alpha-gal is produced heavily in animals with lots of red meat...such as bovines, sheep, and pigs. The allergic response to red meat experienced by patients with red meat allergies is mediated, like most other allergic responses, by IgE.

The Lone Star Tick
There is strong evidence to support the involvement of various arthropods in the development of red meat allergies, however, the mechanisms have yet to be completely worked out and at this point causation has not been fully established between red meat allergy development and tick bites. So far, scientists have been able to establish that IgE antibodies to alpha-gal are specific to regions where tick bites are common problems. In particular, epidemiological evidence has focused around Amblyomma americanum, the lone star tick. Researchers have also found correlations between IgE antibodies that are specific for both proteins from ticks and for alpha-gal. This means that humans may be producing alpha-gal IgE in response to tick bites, which may, in turn, be associated with red meat allergic responses.

Another paper published this year (2014) describes a case of a patient suffering from problems for 4 years who was finally diagnosed with a red meat allergy based on IgE Ab alpha-gal titers. This study, along with previous studies from both the US and Europe strongly support the notion that tick bites have the potential to alter our immune systems in such a way as to elicit anaphylactic responses after the ingestion of red meat.

Interestingly, ticks aren't the only arthropods demonstrated to cause changes in alpha-gal antibody production. It appears that people with Chagas' disease and with Leishmania also have significant increases in serum titers of these antibodies. Both of these diseases are vectored by arthropods (kissing bugs and sandflies respectively).

As with many immunological studies, the answers to the questions how and why are far from straightforward. Much work is yet to be conducted regarding the relationship between ticks, alpha-gal, IgE, and red meat allergies. With enough time and effort, perhaps we will be able to elucidate the intricacies of these interactions so that people afflicted by these allergies will be able to eat red meat once more. In the meantime, we will continue to study this bizarre reaction and attempt to better understand its origins so that we can learn how to offset its effects.