Parasites Can also Be Parasitized
As for medical treatment, many bacteriophages are able to control the proliferation of bacteria.
When it comes to triggering a panic in human beings, I'm afraid few creatures can be as successful as parasites: roundworms that colonize the digestive tract, Fasciola hepatica that invades the liver and plasmodia that kill people invisibly...
A 3-year-old boy’s intestine was clogged by worms. Image source: Wikipedia
Even movies are keen to borrow scary images of parasites, such as the venom in Marvel movies, the Facehugger in Alien, and the mutant gordius in Deranged...
The Facehugger in the Movie Alien
However, what you might not expect is that parasites that survive by sucking the flesh and blood of their hosts may also be reduced to weak and helpless hosts in the eyes of other parasites...
What is Hyperparasitism?
This is a story that “a mantis hunts cicadas, and a finch is just behind them”. Hyperparasitism occurs when one kind of parasite is parasitized by another kind of parasite. Sometimes, this parasitic relationship can even evolve into tertiary parasitism and quaternary parasitism.
For instance, the larvae of Pieris rapae are parasitized by Cotesia glomerata, and Cotesia glomerata, a small parasitic wasp is in turn parasitized by Lysibia nana. Cotesia glomerata and Lysibia nana are considered to be parasitic and hyperparasitic wasps of Pieris rapae, respectively.
Lysibia nana. Image source: Wikipedia
Typical hyperparasites mainly exist in insects, especially in Apocrita, Diptera and Coleoptera in the order Hymenoptera. At present, 17 families in Hymenoptera and a few species in Diptera and Coleoptera are known as hyperparasites.
The plant world also has a weird hyperparasitism relationship. There is a kind of plant called phacellaria rigidula benth, a species in the genus Phacellaria of the family Santalaceae. This kind of plant usually parasitizes on the branches and tendrils of plants, such as loranthus parasiticus and mistletoe, while loranthus parasiticus, mistletoe and other plants semi-parasitize on the branches and tips of woody trees. Hyperparasitic plants often have no stems or leaves, and cluster on host plants.
A kind hyperparasitism. Image source: phytoimages
Is the Essence of the World Matryoshka Dolls?
The above are some simple parasitic relationships. There are many other parasitic relationships in nature. A typical example is a quintuple parasitic relationship found in a microbiology lab. In this case, the parasitic relationship starts with a nestling. The larvae of Calliphoridae parasitize the abdomen of the nestling and feed on blood, while the larvae are in turn parasitized by a parasitic wasp, which carries some sort of bacteria- Wolbachia (one of the most widely distributed symbiotic bacteria in the world), and Wolbachia itself is invaded by bacteriophages. The latter copies themselves inside bacteria. This parasitic relationship is fivefold and just like matryoshka dolls, isn't it?
Nevertheless, the parasitic relationship doesn't stop short at this point. The smallest parasite is probably a transposon. It cannot be regarded as an organism, but a special kind of gene fragment, which can replicate solely and the replicated fragment is inserted into different sites in other genetic sequences, just like parasites that parasitize in genes. In addition, the transposon can also interfere with the normal function of genes, much like the damage of parasites to their hosts.
Mutual Restriction in Hyperparasitism
It is believed that the hyperparasitic relationship is similar to the relationship among grasses, herbivores and carnivores. They are mutually restrictive.
Examples of such kind of mutual restriction do exist. For example, there is a fungus called Ophiocordyceps unilateralis. It likes parasitizing in the body of Camponotus leonardi.
An ant infected with Ophiocordyceps unilateralis. Image source: Wikipedia
Furthermore, Ophiocordyceps unilateralis can change the behavior pattern of ants, make them leave their original foraging path and residence, and move to areas where the temperature and humidity are suitable for growth of fungi. Subsequently, these ants will bite the leaf veins firmly until the latter dies. In this process, Ophiocordyceps unilateralis will grow fruiting bodies from the head of ants and release spores to finish the process of reproduction.
Be that as it may, Camponotus leonardi can't just await their doom. They should learn to “cope with bacteria with bacteria”. Ophiocordyceps unilateralis is parasitized by another fungus, which can destroy Ophiocordyceps unilateralis. Accordingly, the ants allow this fungus to spread across the ant colony by grooming each other, with a view to limit the destructive power of Ophiocordyceps unilateralis to the ant colony, and the relationship among the three strikes a balance.
Hyperparasitism Can also Cure Diseases
Perhaps inspired by this, someone began to investigate the application value of hyperparasites in pest control and medicine.
For instance, cryphonectria parasitica is a fungus that can do serious harm to chestnut trees in America (chestnut blight is also one of the most important forest diseases). However, there is a virus, i.e., low-virulence virus CHV1. It can be transmitted in cryphonectria parasitica and induce female infertility among cryphonectria parasitica. The destructive power of cryphonectria parasitica can be effectively alleviated by artificially releasing cryphonectria parasitica infected with low-virulence virus CHV1. This biological control mode has already borne some fruit.
Cryphonectria parasitica infection causes the bark to crack. Image source: Wikipedia
As for medical treatment, many bacteriophages are able to control the proliferation of bacteria. If they are used to treat diseases, they will be much more effective than antibiotics. At present, many researchers have regarded bacteriophage therapy as a way to fight against superbacteria. Perhaps someday, we can use bacteriophages “drugs”.
