Category Archives: Braaaains!

Update on Zombie Ants

BRAAAAAINS!

BRAAAAAINS!

Hello, and welcome to all new/returning YCP students! Additionally, welcome to all new BIO230 students–I hope everyone has had a restful and relaxing summer break. I know I sure did; I had fun during summer Micro, had a week long break, and accomplished some important Science in my spare time. One thing I did not do was update this forum. Looking back, it appears I last opened up WordPress back sometime in April. Let’s see if we can do something about that!

I found a news alert on ASM’s Microbe World site, which gives an update on the Zombie Ant story. It summarized work out of the entomology department at Penn State University, which has been studying a fascinating example of symbiosis between an insect and a fungus called Ophiocordyceps. What is most interesting about this relationship is that infection by the fungus causes behavioral changes in the host. These changes are advantageous for the fungus–the ant moves over a greater range, allowing the spores of the fungus to spread further. Obviously, infection of a colony would be a Bad Thing, leading to this observation on the phenomenon of “Social Immunity”.

Social Immunity has been observed in laboratory settings in a variety of insect species. It prevents the spread of diseases within colonies, however it has not been previously observed in field conditions. In a study published recently in PLOS One, researchers placed ants which had been freshly killed by the fungus inside one of two nests; one nest had live ants, and the second nest had no ants. The fungus-killed ants were rapidly removed from the living nest, and no further fungal infection occurred of that colony. This result suggests that effective reproduction of the fungus requires being outside of the colony.

In an expanded study, researchers examined the dynamics between the appearance of infected dead ants outside of colonies (sources of infection) and the position of foraging trails (future hosts) in several colonies over the course of 20 months. The researchers observed a consistent appearance of 14.5 cadaver ants per month per colony. Based on this low rate of infection and the lack of colony collapse, the researchers proposed that this fungal parasite represents  a “chronic” infection of these colonies. The authors suggest that the removal of corpses from the colony or ants dying in isolation outside the colony may be an essential step in the development of Ophiocordyceps to a stage that enables the fungus to infect a new host.

Malaria and foot odor-the missing link!

Via Gawker.com and the LA Times, here’s a news alert that all college students should be mindful of. Researchers at the London School of Hygiene and Tropical Medicine have published in the medical journal PLOS One a new defense against malaria transmission. Malaria is a disease which affects a large proportion of the world’s population, with an estimated 220 million cases (nearly 1 in 20 people) worldwide in 2010. It is caused by the several species of the protozoan genus Plasmodium, and transmission requires specific species of mosquitoes that are essential for the life cycle of Plasmodium. There are treatments for malaria that can help infected patients to clear the parasite, but there is currently no vaccine. Main methods for control for the transmission of malaria have traditionally focused on controlling the reproduction of mosquitoes.

The experiments conducted by the researchers were simple; new adult female mosquitoes were fed human blood which was either infected or uninfected with Plasmodium. Following verification of infection, mosquitoes were introduced to socks (20 Den panty sock, HEMA, The Netherlands) that had been worn for 20 hours beforehand

…by a male volunteer of whom the relative attractiveness to An. gambiae s.s. compared to 47 other men is known…

Control socks, of course, were fresh right out of the package. The researchers constructed a mesh matrix, and measured the rate at which the mosquitoes landed on the matrix (landing rate).

journal.pone.0063602.g001

As can be clearly noted from their data figure, infected mosquitoes were 4 times as likely to be attracted to the human odor than uninfected mosquitoes. The authors conclude that the presence of Plasmodium is altering the behavior of the mosquitoes, which may increase the rate of transmission as the population of infected vectors (the mosquitoes) rises. They suggest that current mathematical models for malaria transmission may be underestimating the rate at which the protozoan spreads through populations, as generally uninfected mosquitoes are used in behavioral studies and do not take into account the effects of the parasites themselves on vector-host interactions. Effective malaria control programs need to accurately model all aspects of parasite/vector/host interactions.

From the point of view of the pathogen (Plasmodium,) this is a perfect strategy. Plasmodium species depend upon the mosquito vector for the sexual portion of their life cycle, and this requires approximately 2 to 3 weeks to occur. As this occurs, it is advantageous for the organism not to be transmitted to a new host during a blood meal. However, after sexual maturation has occurred and the new sporozoites migrate to the salivary glands of the mosquito, modification of behavior will allow the subsequent transmission back into a new host during as the mosquito feeds. Long time fans of BIO230 will recall how another Apicomplexan protozoan, Toxoplasma gondii, has been found to potentially modify its host’s behavior, leading to the inappropriately named “Crazy Cat Lady Syndrome.”

How to destroy the world

The assigned task is actually going to be easiest with microorganisms. I came across Plague, Inc; a game designed for both iPad/iPhone and Android platforms that aims to be a simulator of how a disease could develop to destroy humanity.  Created by Ndemic Creations, it is very approachable and lends itself to experimentation. You start off the game by choosing a type of pathogen (bacterium, virus, fungus, prion, nano-particle) and inflict it on Patient Zero in a country also of your choice. First world countries would allow your pathogen to quickly spread to other countries, however the public infrastructure would also allow a more rapid medical response to the outbreak.

Uh oh; all of the Western hemisphere except Canada looks like it is in trouble!

Your task at that point is to try to stay ahead of the effort to cure the disease. This is accomplished by increasing the rate of transmission, the symptoms, and virulence of the pathogen. Increasing transmissibility early allows the pathogen to gain a toehold in many countries quickly, however many millions of infected people with no deaths is not a useful strategy. A balance between infectious potential and lethality is essential, and the balance depends upon the class of pathogen played. For instance, an outbreak of a pathogen that is more lethal than it is transmissible will quickly be eliminated, as victims die before they can pass it on to healthy individuals.

The object of the game is to kill all life on Earth. During the endgame as seaports and airports are shutting down, you find yourself hoping that you’ve managed to introduce the pathogen into all countries. In one game I found myself with a pocket of healthy people in a lone country, while the rest of the world population quietly died off. Ultimately, I had no way to introduce the disease into that pocket of survivors.

The games simulates some aspects of a disease outbreak very well, showing that transmission rates can be increased by allowing the pathogen to be spread via airborne, waterborne, and by various vector methods of transfer. The game does make one assumption with the host/pathogen interaction that does greatly simplify things, but also is not particularly realistic. The game assumes that once infection occurs in an individual, the individual is permanently infected at that point unless one of two things occurs: the patient is “cured” during the endgame, or the patient dies of the infection. There is a third alternative, which is that the patient’s immune system combats the infection and eliminates it. What the immune system would enter into the equation is that the pool of infected individuals would constantly be in flux, as was described in my posting about Bieber Fever from earlier in the summer. While this doesn’t detract from the central premise of the game that the interaction between host and pathogen is complex, playing this game should NOT be taken as a substitute for reading Chapter 14 from Microbiology by Bauman.

All in all, I give this game 4.5 BIOHAZARD symbols out of 5; it is a fun, quick way to see how virulence of a microorganism can affect how it might spread through a population. For 99 cents from iTunes, it is definitely a good deal. And a special BONUS for Lynn B. from last semester: one of the powerups for symptoms is “Walking Dead.”  There’s your Zombie Apocalypse right there!

More on Justin Bieber

The Justin Bieber: Public Health Catastrophe post the other day generated the largest number of non-Bonus Point bribed comments of any YCPMicro posting to date.  So it occurred to me that combining Justin Bieber with the also-very-popular “zombies” tag, that I could generate the perfect blog posting.  Here you go:

That hair is impeccable! Even with a grub crawling out of his eye.

In an attempt to direct future content on the YCPMicro site, please take my brief poll:

Zombie Humans: Now in the news

Hot on the heels of my last Zombie Ants update, one of the most significant Google search trends for early June 2012 is “Zombie Apocalypse.”  This has been in response to several high profile news items over the past few weeks, including the curious case of Rudy Eugene, who was shot multiple times by responding police officers as he was caught eating the face of his victim. The graphic nature of the attack and the intense media coverage has led to speculation that an illicit drug known as “bath salts” was responsible for Eugene’s behavior, however toxicology results have not been completed yet.

Mephedrone, or “bath salts”, is a synthetic stimulant of the amphetamine class of drugs. As an analog of other illegal stimulants in the United States, it is also considered illegal for use. The drug produces a variety of effects when taken, and is a powerful stimulant. A number of deaths have been noted worldwide due to consumption of mephedrone. Misrepresentative labeling of mephedrone containing compounds has led to their relatively easy access currently in the US and elsewhere. The labeling of mephedrone as “bath salts” is one way for producers of the compound to skirt legality.

So what about zombies? The Centers for Disease Control put up a blog entry in May 2011, which gave very good information describing how Americans could best prepare themselves in case of a serious natural disaster. The website included several excellent recommendations including: a source of clean water (1 gallon per person per day), non-perishable food, a supply of prescription and non-prescription medicines, and a small toolbox with useful supplies like a utility knife, duct tape, and a battery powered radio. The website was designed with preparing citizens for disasters such as “tornadoes and hurricanes,” however the site had the tongue-in-cheek title “Preparedness 101: Zombie Apocalypse.”

This well meaning intention has had the unfortunate effect of making it seem that the CDC has had realistic concerns about the feasibility of zombies, and that somehow the spate of recent news stories somehow has a basis with fictional zombies. In response, the CDC has had to come out on record with the statement that the

CDC does not know of a virus or condition that would reanimate the dead (or one that would present zombie-like symptoms)

So rest assured, if you get attacked by your roommate, they are likely not really a zombie. Stephen Colbert, however, thinks otherwise!

BONUS TIME!  List in the comment thread an actual infectious disease that can modify the behavior of humans!

Zombie Ants: again in the news

Zombies Ants, now after BRAINNNNS!

One of the strangest articles I’ve come across recently was this story about the odd symbiotic relationship between an ant species, and a fungus that essentially turns the ants into zombies.  To summarize for those students unwilling to click the link and read that summary, the fungus Ophiocordyceps would colonize a particular species of ant while it was still alive, and modify the behavior of the ant. This enabled the fungus to use the ants to spread out over a large geographical region, a novel way for a sedentary species like a fungus to spread its genes.

Researchers at Penn State University have followed up their initial report, that again is being widely reported in the media (I heard about it first via National Public Radio.) It seems that the interaction between the ants and their parasitic fungal species is far more complicated than proposed earlier, and this new study models the spread of the fungus within the population of ants in a colony, as opposed to between individuals.

The ant species examined in this study is a relatively long-lived species, indicating a low mortality rate among individuals. The high density of individuals in an insect colony means that the risk due to infection is high, but that significant defenses against infection need to be present. The researchers found that the percentage of Ophiocordyceps infected ant corpses was significantly lower than the total number of ant corpses in graveyard sites near the ant colonies. However, many corpses were hyperparasitized by other fungal species, a situation which appeared to prevent the colonization by the “zombie” fungus Ophiocordyceps.

What the model suggests is that what the “parasite” fungus does is to prevent the spores of the “zombie” fungus from maturing, and prevents the latter species from taking over the ant colony. Previous models of the dynamics of ant hosts and their pathogens had suggested that the two players shared a complicated set of interactions; ants developed behaviors to minimize the risks of infections, which the fungus further modified the host behavior to their advantage. The current report underscores that a third party also must be included in the web of interactions, and that the other fungal species that can further parasitize the ants are significant players.

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