Parasites are one of the nastiest things that nature has provided our beloved planet. They can manipulate the human brain, rewrite DNA and even turn a host into a living dead. Parasites range from one-celled organisms to relatively large tape worms. In this post, we look at the five most dangerous parasites known to man.

1. Naeglria fowleri

Otherwise known as brain-eating amoeba, Naelglria fowleri is a free-living and single-celled organism that thrives in water. It causes a rare brain condition known as meningoencephalites, which leads to severe inflammation of the brain.

It infects people when contaminated water enters the human body through the nose. It travels to the brain where it starts damaging the brain tissue. This parasite is found throughout the world and is common in the south-tier states of the United States. It cannot thrive in oceans or salt water.

Symptoms of Naelglria fowleri infection appear in less than a week and include headache, nausea, vomiting as well as stiffness in the neck. Advanced symptoms include loss of balance, lack of attention, hallucinations, seizures, coma and death. According to the CDC, this infection has a nearly 100% immortality rate.

2. Ixodes holocylus

Ixodes holocylus is commonly known as the Australian paralysis tick and as the name suggests, this parasite can cause paralysis by releasing a neurotoxin into its host. Once the neurotoxin is in the body, it can cause respiratory failure if it reaches the lungs.

The symptoms of a neurotoxin infection by Ixodes holocylus appear as a normal ascending flaccid paralysis. Initial symptoms include restlessness, myalgias, paraesthesias, fatigue and irritability.

Within 12-24 hours of infection, any muscles inverted by facial nerves become weaker. Respiratory muscles start failing if the tick isn't removed and eventually, the patient dies of respiratory failure.

3. Taenia solium

Otherwise known as pork tapeworm, Taenia solium makes its way to the body when a human ingests eggs with infective larvae. The egg shells are broken down in the intestines and the larvae enter the bloodstream. This parasite has been known to settle in many kinds of blood tissues and sometimes enters the central nervous system.

Taenia solium infection can lead to epileptic seizures (neurocysticercosis). This condition is not easy to diagnose as it doesn't have specific symptoms. A few cases of this disease have been reported in the US and UK. It is also common in South America, sub-Saharan Africa and Asia.

4. Halicephalobus gingivalis

While generally harmless, Halicephalobus gingivalis can sometimes prove fatal to human beings. It has been known to cause neurological infections in horses in the US, UK, Japan, Iceland and Canada.

Human infection cases are rare and if they do occur, it only affects individuals with compromised immune systems. The outcome of such an infection is usually fatal and leads to meningo-encephalomyelitis. This refers to an inflammation of the spinal cord, brain and their membranes.

5. Dracunculus medinensis

It is also known as Guinea Worm and infects humans when they drink contaminated water containing water fleas that have the worm's larvae. Rather than get digested like the fleas, the larvae penetrate the wall of the stomach or intestines and make their way to the body cavity. They live there for about a year, when the female guinea worms have grown to more than 18 inches.

They move down from the pelvis towards the foot, which can result in an intensively painful and burning sensation. This is usually the first sign of guinea worm infection. Once it reaches the skin, it emerges from a blister and releases thousands of larvae when it encounters water. The parasite doesn't cause death, but it can cause excruciating pain and severe allergic reactions. Secondary infections can also occur if the guinea worm dies before emerging.

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