Under a microscope, they look like alien creatures or monsters that crept right out of your nightmares. It's difficult to believe that these tiny little parasites can do such great damage when they enter the human body. Some parasites may go through their entire life cycle with minimal effect on humans, while others may cause debilitating pain and even death when not treated early enough.

Here is a list of 10 creepy, parasites that humans need to watch out for:

Wuchereria bancrofti 

This roundworm enters the human bloodstream via carrier mosquitos. In a year, the larvae mature within the lymphatic system, and if left undetected and untreated, can cause elephantiasis, which causes the skin to become thicker, especially around the lower limbs and even the male genital area.

Loa loa

The African Eye Worm dwells in the blood just underneath the skin but is most obvious when it reaches the white parts of the host's eye. Complications from infection usually occur in tourists to West Africa. Patients have reported pain as the parasite traverses the eye or the nose bridge and some have even said they can see the worm crawling across the eye. When the worm dies, swelling - mostly in the forearms and wrists - are caused by an allergic reaction, but do not cause long-term damage.

Toxoplasma gondii

This parasite reproduces in the intestines of housecats and when they infect rodents, cause the mice and rats to actually become attracted to the smell of feline urine and become easy targets for the parasite's host. When humans are infected with the single-cell organism, some studies have shown links with schizophrenia, self-mutilation, and slow reaction times which increase the risk for getting into traffic accidents.


This flat, segmented worm usually infects animals that drink from contaminated water sources but can also invade humans who eat undercooked meat of infected animals, or from improper handling of food by an infected person. The worms are normally passed through bowel movements and if the infection is severe enough, will cause blockage in the intestines. If left untreated, the worms can be passed to the liver, heart, eyes, and brain and become fatal.

Dracunculus medinensis 

Also known as the guinea worm, this parasite lays its eggs in stagnant water where the larvae will attach themselves to water fleas. They enter the human body when humans swim in affected water, or drink water containing infected water fleas. Inside the body, the fleas die, leaving only the guinea worm to thrive. If undetected, the worm can grow up to three feet long inside the body and will begin to burrow itself out, causing a burning sensation on the skin. If a person tries to ease this burning and inflammation by swimming in cool water, the worm will spew its eggs out through the wound, into the water. Although guinea worm disease is normally not life-threatening, the pain it causes and other complications can make it severely difficult to move around and cause disability.

Gnathostoma Spinigerum 

This is a parasite that lives in eels and can spread to humans who eat the raw or undercooked fish. Symptoms include swelling under the skin; however, even though it can live inside the body for up to a decade, the human body is not the ideal environment for the parasite; it cannot reproduce and multiply inside the infected humans. It is a rare parasite with even fewer instances of the worms burrowing deeper into the organs and become life threatening.


This vampire fish of the Amazon has an ugly reputation. Internet horror stories abound about the fish burrowing up a person's urinary track, causing intense pain, agony, and even death. Fortunately for humans and candiru, according to Dr. Irmgard L. Bauer, who wrote about the parasitic catfish in the Journal of Travel Medicine, there is absolutely no conclusive historical or medical evidence that any of that is true.

Giardia lamblia 

Once Giardia lamblia enters the body through contaminated water, it colonizes the small intestines and causes diarrhea, flatulence, sulphuric-tasting, burping that are so foul-tasting they cause you to vomit, pain, lack of appetite, and blood in the stools.

Sarcoptes scabiei 

Scabies, or itch mites, infect humans, cats, dogs, pigs, koalas, wild boars, great apes, and other animals. They can cause mange due to damage cause from itching at night. It is spread through skin-to-skin contact and although an infestation may be difficult to eradicate in a herd, it can be treated in humans with topical creams and ointments.

Ascaris lumbricoides 

The most common parasite that infects humans is the roundworm. Poor sanitation in developing, tropical countries is where the most cases are reported - especially areas where human feces are used as crop fertilizers. Once the eggs are swallowed, the larvae hatch and burrow through the intestines and through the bloodstream until they reach the heart and lungs. Most of the time, the infection is asymptomatic, and the worms can remain undetected in the body for years. But common symptoms can include coughing up blood, difficulty breathing, and worms in vomit or stool. Infections are usually treated with three days of prescription medicine which block the roundworms from receiving nutrients until they die.

Parasites that can infect people are everywhere. But in order to minimize risk of them feasting in your body, avoid areas with known outbreaks; always wash your hands and put on mosquito repellant, especially when visiting tropical countries; and, according to Parasite in Humans, exercise can help keep lymphatic fluids in the body move and drain, and help white blood cells shift to areas of infection faster.

ⓒ 2021 TECHTIMES.com All rights reserved. Do not reproduce without permission.