Mind-controlling parasites

Nature is a fabric of life which connects every living organism in the earth. There are so many different interactions between organisms. Sometimes, these interactions are not very common, but they are amazing. When you read the topic of this article, you will realize it as a concept in science fiction. If you think like that, you are wrong. The mind-controlling parasites are not an imagination, they exist in reality. These parasites can infect and control the host nervous system. Then the host behaviour manipulates according to the parasite’s requirements. The host organisms act like zombies whose minds are controlled by parasites. Such parasites have co-evolved with its respective host organism over millions of years. During this evolutionary journey, parasites have developed advanced strategies to disrupt the hosts’ neurochemical systems for ensuring their existence. The most common host organism group in this unique interaction is insects, but mammals such as rats and cats can also act as host organisms. Some of parasitic fungus, virus, flatworms and protozoa have the ability to taps into a host neuronal system, altering the host cognitive functions. After the parasite infection, host shows various behavioural changes such as suicidal behaviour, bodyguard behaviour and abnormal moving behaviour. The nature of the manipulated behaviour depends on the parasite life cycle. Most of the time, altered host behaviour helps parasite to complete the stages of its life cycle. Now, I’m sure that you need to know about real-world examples. The rest of the article presents examples of mind-controlling parasite-host interaction.

A parasitic fungus called Ophiocordyceps unilateralis can infect ant species (Camponotus Leonardi), which leads to the suicidal behaviour of the ant. During the foraging time, fungal spores attach to the cuticle of the ant body. Following the germination of the spores, fungal germ tube penetrates the body through the cuticle. Since then, fungal filaments called mycelia grow inside the ant body, degrading host tissues. To our surprise, this fungus grows inside the ant body but avoiding main organs. The host organism remains alive until the completion of the parasite’s end goal. Then fungus releases a chemical, which has not been identified yet, for altering the host behaviour. All infected ants exit the colony before the death because dying inside is not favourable for fungal dispersion. Ants remove their dead nest-mates quickly. Thus, there is no sufficient time for large stalk formation from the back of the ant’s head. The spore structure formation is essential for propulsive release of spores into the environment. Thus, fungus controls infected ants’ behaviour to ensure optimum spore distribution. The zombie ants climb to the top of the tree and clamp its mandibles around a leaf or leaf stem. This final death grip causes due to the excessive atrophy of mandibular muscle. The rapid fungal growth surrounding the brain results from atrophy of mandibular muscle. After the last death grip, ants die and stalk formation initiates, fulfilling the fungal parasite end goal. It is an example of suicidal behaviour, which induced by mind-parasite. Another parasite called hairworm (Paragordius tricuspidatus) infect crickets and control their behaviour by directing them to commit suicide in water. The aquatic environment is necessary for the reproduction of the hairworms. Thus, hairworms can complete their life cycle via these zombie insects.

Some parasites protect their offspring within the host body by controlling host behaviour. Such behavioural manipulation called as bodyguard behaviour. There is a wasp species (Dinocampus coccinellae), which has the ability of mind-controlling in other insects to safeguard its offspring. They sting and insert one egg into the ladybug (Coleomegilla maculate) body. The wasp larvae develop inside the ladybug body for about 20 days and emerge from the host body. The host is still alive because the parasite end goal is not over. Then the emerged wasp larvae make a cocoon around its body and ladybug remains half-paralyzed on the top of the cocoon. This ladybug always twitches its spotted red carapace to protect the wasp pupa from the potential predators. This peculiar behaviour of the host causes by a virus, which lives inside the wasp body. During the egg insertion process, this virus transmits to the ladybug. At the time of the larvae emerging, virus able to replicate inside the host nervous tissues. It causes symptoms such as motor twitches, which protect the wasp pupa. It is a complex parasitic interaction, which involves three organisms. The existence of the virus depends on the survival of its vector, the wasp species. Thus, viral species induces the manipulated behaviour in the host to ensure the existence of the wasp species. A parasitized caterpillar species (Thyrinteina leucocerae) also show similar bodyguard behaviour. A different wasp species (Glyptapanteles sp.) sting and insert eggs inside the caterpillar. The many developed wasp larvae emerge from the host body after two weeks, but two or three larvae remain inside the body. These remaining larvae control the mind of the host for protecting their pupating siblings. The caterpillar starts to snap its upper body back and forth and keep predators away from the wasp pupa. However, this mind-controlling mechanism is still unknown.

Toxoplasma gondii is a protozoan parasite, which infects warm-blooded vertebrates. However, this parasite only able to complete the reproductive stage of the life cycle inside felines (members of the cat family), even though the parasite has a broad host range. Toxoplasma gondii produces loads of oocysts during the reproductive stage inside felines. Cat faeces that consist of parasite’s oocytes act as the main source of parasitic distribution. This protozoan parasite infects rats and controls their minds by an unknown mechanism to ensure the completion of the reproductive stage within felines. Normal rats can detect the smell of cat faeces and run away from these areas. Contrastingly, infected rats are attracted to the cat faeces due to the influence of the parasite. These infected rats show less fear in front of cats, which leads rats to become easy pray for cats. After cats eat infected rats, protozoan parasite starts the reproductive phase inside the cat body. Not only the rats and the cats, but also humans get infected. Toxoplasma can not complete life cycle inside humans. Around one-third of humans has infected by this parasite, but most of them doesn’t show any symptoms. There are some evidences about the behavioural changes following the infection in humans that are related to risk taking behaviour. However, Toxoplasma infection is also associated with neurological diseases in immunocompromised humans.

These different types of examples for the interaction between the host and the mind-controlling parasite show you the remarkable nature of the organization for ensuring the existence of parasites in the environment. The interactions between host and some parasite are complex than we think. I’m sure that you will realize the superpowers hide inside these tiny parasites. In the end, I can tell you one thing. Nature is incredible. It is a mystery that we cannot ever fully reveal!