We have heard of parasites and how they can feed off another organism, nourishing itself while devoiding the host of nourishment. They can be dangerous—as dangerous as bringing about a drastic environmental change or causing the death of a human being. On Earth, there are many bizarre parasites that can do things that are like themes in our nightmares. The word “parasite” comes from the Greek word “parasitos” which was a term for a person who is eating at another’s table. “Parasitos” is a combination of the two Greek words “para” which means “alongside” and “sitos” which means “food.” Here is a list of some bizarre parasites and their dangerous ways.

1 Toxoplasma gondii is a brain parasite spread through cat feces can be transmitted to humans. It can cause humans to care for their cats excessively along with causing several neurological disorders. It brings about a “fatal attraction” in mice towards cats and slows them down, making them easy prey.

Found across the globe, Toxoplasma gondii (T. gondii) is known to have affected 50-80% of the human population at some point in time according to serological studies. In France, the highest concentration of infected persons (84%) has been found. It can affect all warm-blooded animals but can multiply only through cats. This deadly parasite is known to cause the same alterations in a human mind as it causes in mice. When mice are infected after ingesting the oocysts (the offspring of the parasites) shed in the feces of the cats, their guard is let down making them less risk-averse and they become slow and are an easy prey for cats. To make matters worse, the fear in the minds of the hosts, including mice, vanishes causing the “fatal attraction phenomenon” where the mice are attracted to the cat’s odor. Even male humans who were infected found the odor of cat urine to be “more pleasant” than the ones who were not infected. In women, the effect was the opposite.

In humans, this parasite can cause several pathological behavioral alterations and serious neurological disorders such as schizophrenia, obsessive-compulsive disorder, aggression, and bipolar disorder. In healthy individuals, it produces mild flu-like symptoms, but in infants and patients with weak immunity, it can cause a disease called “toxoplasmosis” which can be fatal. It makes humans love and care for their cats more than usual, and that is the reason why toxoplasmosis is dubbed as the “Crazy Cat Lady Syndrome.” It could be a reason why some people obsess over cats. (1,2)

2 Cymothoa exigua is a parasite that severs the blood vessels of a fish’s tongue and becomes a new functional tongue itself. It is the only known parasite to replace an entire organ in the host organism.

Also known as “tongue-eating louse,” Cymothoa exigua (C. exigua) enters a fish’s body through its gills. The male attaches itself to the arches beneath fish’s gill and the female attaches itself to the fish’s tongue. This 8-29-millimeter-long parasite severs the blood vessels of the fish’s tongue causing it to atrophy from lack of blood, eventually making it fall of its mouth. C. exigua then becomes the fish’s new tongue and feeds on the fish’s blood and mucus to survive. When the fish dies, it detaches itself and hangs on the outside of the fish’s body. What happens to the parasite after that is not known. Another striking feature of this parasite aside from it being the only known one to replace an entire organ of its host is that the male can turn into a female once it becomes 10 millimeters long.

Found in the waters of the south of Gulf of California to the north of Gulf of Guayaquil, Ecuador, the parasite is also found in Atlantic waters. C. exigua is not believed to be harmful to humans currently unless the parasite is picked up alive by a human. When that happens, it can bite a person. It is a shocking fact that isopods like C. exigua are often found attached to aquatic animals and consumed by humans regularly. They are not poisonous to humans. (source)

3 Phronima is the alien in the movie Alien which was inspired by a transparent, deep-sea parasite that eats other creatures from the inside out and then takes over their bodies to ride the seas in the carcass and lay its eggs.

Phronima adds more weight to the saying “truth is stranger than fiction.” This parasite, more technically, a “parasitoid,” inspired the fictional, extraterrestrial species character who is the antagonist in the movie series Alien. Phronima is found throughout the world’s oceans except in the polar region and is unique. The female, which attacks the salps (a zooplankton), then uses its claws to eat the animal, forming a hollow in its body. It then enters the barrel-like, hollow body of its prey and travels the waters using it as a vehicle. In the same gelatinous barrel, the females lay their eggs and nourish their larvae. The structure of the barrel enables the parasite to be more buoyant in the water. The characteristics of Phronima is not completely known as it needs to studied alive and that is very difficult. Many of the aspects of Phronima’s life remain a mystery to science. (source)

4 Spinochordodes tellinii is a parasitic worm that develops in grasshoppers which, when fully grown, makes the grasshopper jump into the water, causing it to drown.

Spinochordodes tellinii (S. tellinii) is one vindictive parasite. This parasitic worm that can grow into a size that is three to four times longer than the host grasshopper, enter their host’s body in the form of larvae through the intake of food. Eventually, taking nourishment from the grasshoppers and crickets, they grow strong enough to control their behavior. It influences the grasshopper to jump into a water body where it can easily drown. It does this so that it can leave the body of the grasshopper and reproduce in the water. The parasite does not influence the grasshopper to actively seek water but does so only when it near to a water body. It was revealed in a study in 2015 that the infected grasshoppers create different proteins in their brains than the uninfected ones which are directly a result of the infection by S. tellinii. (source)

5 Naegleria fowleri is a freshwater parasite that can enter the human brain through the nasal cavity while swimming in freshwater lakes or poorly sanitized pools. The parasite destroys human brain tissue and has a fatality rate of 97%.

Known as the “brain-eating amoeba,” Naegleria fowleri is an organism that will make you think twice before you jump into a water body to swim next time. Found in warm, freshwater lakes and rivers and in poorly sanitized pools, the parasite targets children and teenagers. Once infected, the chances of survival are only 3%. It causes a swelling in the brain called “primary meningoencephalitis,” and within days, a person can die. However, infection from this parasite is rare and in some cases, can be treated. Only 34 cases were reported in the United States from 2004-2014. Scientists are concerned that climate change could help this parasite thrive as it needs warm water bodies.

Naegleria fowleri can only enter the human body when the water enters inside the nasal cavity. It burrows into the olfactory nerve that leads directly to the brain. Using its suction-cup like structures, it feeds on the brain tissue giving rise to the very first symptoms of infection—a loss of smell and taste. As the infection progresses, it can cause hallucinations, seizures, and confusion. As the body fights against the infection, it causes inflammation and extreme pressure on the skull which pushes the brain downwards severing the connection with the spinal cord causing death. Using nose plugs and not immersing the head under the water can help in preventing the infection. (source)