Pretty much everyone gets infected by a cold virus at some point in their lives, but there are much stranger infectious entities in the world. Let's take a look at...
- The gigantic virus mistaken for bacteria
- The brain-eating amoeba
- The minuscule viroids (from early Earth)
- The spider-zombifying fungus
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| Cordyceps fungi can control the behavior of their victims... (Docujeju) |
The Gigantic Virus Mistaken for Bacteria
Most viruses are tiny things, consisting of little more than a clump of genetic material inside a protein shell. In fact, they are so stripped down that most biologists don't consider them to be actually alive. Of course, there are always exceptions...
In 1992, investigation into a pneumonia outbreak in England identified the cooling towers of a power plant supplying Bradford in England as a potential source. Samples from the warm water in the towers contained Legionella bacterium, but they also held amoeba infected with a strange pathogen. This unknown entity was big enough to be seen under a light microscope and researchers assumed it was a bacteria... only to find that it didn't respond to bacteria testing procedures.
Further investigation would eventually reveal this entity to be a giant virus, subsequently named the Acanthamoeba polyphaga Mimivirus. The newly discovered virus lived dangerously, infecting amoeba that were in the process of eating them. Once engulfed by a hungry amoeba, the virus opened a star-shaped hole (the researchers named it a stargate portal, naturally) and fused with the amoeba. The core of the virus then spilled into the amoeba, hijacking it to replicate new copies of the mimivirus.
The researchers also noted similarities between an amoeba and the macrophages found in the human immune system. Both engulf and break down their victims... and it may be that a mimivirus could fuse with a macrophage just like an amoeba.
Mimivirus isn't the only giant virus we've discovered - another set of examples are the nucleo-cytoplasmic large DNA viruses, which are thought to have evolved from a single common ancestor. Members of this group are speculated to have absorbed and incorporated genes from their victims over the eons, resulting in a vast array of different viruses.
Giant viruses may have a thing for cooling towers, as another strain of mimivirus (dubbed mamavirus) was identified at a Paris power plant in 2008. It also has a specialist parasite to call its own, a satellite virus dubbed Sputnik that interferes with mamavirus infection and is considered a virophage.
The Brain-Eating Amoeba
Before you start feeling sorry for the amoeba, you should be aware that some are incredibly dangerous in their own way. Perhaps the worst of them is Naegleria fowleri, the brain-eating amoeba.
Found in warm freshwater and hot springs, this unicellular menace has also turned up in poorly maintained swimming pools... and even tap water. Infection requires tainted water going up the nose - simply swallowing the amoeba doesn't seem to allow it to infect a human victim.
If introduced to the nose, the amoeba can reach the brain and cause primary amebic meningoencephalitis. This infection progresses rapidly in victims as brain tissue swells and dies, with headaches, fever and nausea progressing into confusion, hallucinations, coma and death in a matter of days. This disease is very rare (there are around ten cases each year in the USA) but reported cases have an over 97% mortality rate.
That being said, fast treatment with a cocktail of antimicrobial drugs may save a patient... and people are occasionally found with Naegleria fowleri antibodies that suggest they may have contracted and fought off an infection all by themselves!
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| Giant viruses have been found in more than one power plant cooling tower... (Tama66) |
The Minuscule Viroids (From Early Earth)
The other end of the scale from giant viruses are the viroids, minuscule infectious entities similar (but even simpler than) a virus. While a typical virus consists of a packet of genetic material inside a protein capsule, a viroid forgoes this protective shell. Instead, they are single-strand circular RNA structures that use "rolling replication" to produce new copies of themselves.
The viroids that exist today infect vegetation, specifically plants in the Solanaceae (i.e. tobacco, potatoes, tomatoes etc.) and avocados. One particularly strange viroid that attacks tobacco plants is a "satellite viroid" which relies on an unwitting "helper virus" to soften up the victim.
Researchers believe that these tiny bits of RNA may have had a more impressive role in the past. One theory goes that they may have been the precursors of "normal" viruses or perhaps even served as the origin of all biological life - in which case they could not have originally been parasitic. Despite their minuscule size and simplicity, viroids are still capable of evolution and may have become parasitic only after potential "hosts" evolved.
Curiously, the hepatitis delta virus that infects humans has a lot in common with viroids. It is tiny and relies on hepatitis beta to help it... acting in much the same way as the satellite viroid mentioned above.
The Spider-Zombifying Fungus
If you take any interest in video games or traditional Chinese medicine, you may have heard of Cordyceps fungi. This group of malignant mushrooms parasitize caterpillars and ants, but also alter their victim's behavior to help spread the infection... and in a discovery that blends two horrors into one delightful package, the related Gibellula attenboroughii fungus gives cave spiders the same treatment.
Documentary makers investigating an old gunpowder store room in Northern Ireland's Castle Espie discovered a fungus-coated spider exoskeleton hanging from the ceiling. This behavior would have been very atypical for the cave-dwelling Metellina merianae, a creature that loves to lurk in dark lairs. One scientific investigation later, the culprit behind the mysterious demise was revealed as a behavior altering fungus - the infected victim would be influenced to situate themselves in conditions with good air-flow, ideal for dispersing spores. The fungus then produces a lethal dose of toxins that kills the host, while also saturating the corpse with anti-microbial chemicals - it seems that the fungus doesn't like to share. Now equipped with a succulent spider corpse all to itself, the fungus grows sporing bodies and repeats the cycle anew!
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