Life comes in different types and forms. Sometimes, life uses the sun’s rays to produce energy — like plants. Others feed off of plants or other animals, and some just steal from others. The latter creatures are called parasites, and they can be very dangerous.

We’re never really far away from parasites. There are hundreds of human parasites in the world, constantly looking for ways to get close to you — or inside you. It’s not because you’re special, it’s simply because that’s what parasites do: they live inside your body, feed on you every day, and give birth to more teeny tiny monsters like themselves. 

All such creatures are called parasites, but not all of them are bad. Sometimes, parasites can have surprising benefits, and some of them are even good for the human body, protecting us from some diseases. But then again, others are absolutely dreadful. Here are some of those worst parasites.

10. Blood fluke

Even Napoleon had to face urinary infections due to blood flukes. These notorious parasites cause a condition called schistosomiasis (also known as bilharzia) and to make things worse, there’s not one but more than half a dozen species under the genus Schistosoma that see humans as their host.

The infection occurs via water contaminated with Schistosoma larvae (called cercariae). The larvae penetrate its host’s skin, and then through the blood, it reaches the liver, intestines, urinary tract, and various other parts of the body. Common symptoms of schistosomiasis are itchy skin, stomach ache, diarrhea, etc. However, at later stages, it can cause serious health issues like liver enlargement, haematuria, prostate infection, bladder fibrosis, and infertility.

According to WHO, more than 230 million cases of schistosomiasis have been reported, since the disease was first discovered in 1851. The only parasitic disease that affected more lives than bilharzia is malaria. Fortunately, the infection can be easily treated using an antiparasitic medicine called praziquantel — but if left untreated, the infection can be very painful and unpleasant.

9. Dracunculus (Guinea Worm)

This spaghetti-like nematode parasite may look harmless, but it’s anything but harmless. The parasite causes the Guinea Worm Disease (GWD) in humans, transmitting when a person drinks water that is contaminated with water fleas containing Dracunculus medinensis larvae. The symptoms of the disease start appearing usually one year after the infection when the larva turns into an adult — and things go south very fast.

The adult nematode releases its larvae and comes out of the infected person’s skin by causing blisters. The patient experiences a painful and burning sensation on these blisters and must frequently wash them with water, which prompts the blisters burst and the parasite larvae to be released. The adult also starts appearing out of the blister wounds after a couple of weeks, and this is when it can be pulled out using a small stick. This horrifying process can also cause serious, life-threatening bacterial infections.

Surprisingly, no modern medicine or vaccine can truly treat GWD. It is only when the adult dracunculus decides to show up on skin through wounds, the patient can have the parasite removed from his or her body. 

Dracunculus was formerly endemic to a wide swath of Africa and Eurasia, but it is currently endemic in only five countries: Chad, Ethiopia, Mali, South Sudan, and Angola, with most cases in Chad and Ethiopia. 

8. The tapeworm

Also known by the name Taenia, this ribbon-shaped worm can give you seizures if it manages to form cysts inside your brain. Most commonly though, it finds refuge in people’s (or pets’) intestines.

Taenia Solium larvae may enter inside a person’s body when he or she drinks contaminated water or consumes undercooked pork or beef that contains tapeworm cysts or eggs.

Not every tapeworm-infected person experiences seizures, it happens only when the Taenia larva affects the central nervous system in humans. In these cases, it becomes almost impossible to diagnose or treat the tapeworm infection because the patient doesn’t show any symptoms. Normally, the worm affects the small intestine and causes constipation, diarrhea, abdominal pain, etc. In more severe cases, it may lead to epileptic seizures, blindness, meningitis, and many other neurological problems. Tapeworms are the cause of 30% of epilepsy cases in many endemic areas where people and roaming pigs live in close proximity.

Tapeworms are also one of the most common dangerous parasites. It’s estimated that 5% of Americans have tapeworms, but most aren’t aware of this.

7. Liver fluke

The infection is called fascioliasis and it occurs when an individual consumes raw aquatic plants or water grass containing liver fluke larva. Facial hepatica and Fasciola gigantica are the most common liver fluke parasites found in humans. They mainly infect the bile duct and liver, but in some rare cases, the brain, pancreas, and eyes can also be affected. Research reveals liver fluke poses health threats to more than 150 million people in the world.

However, fascioliasis is not a deadly infection in humans and is mostly found in sheep, but if ignored, the parasite can stay inside your body for up to 30 years and can cause regular gastrointestinal health issues. Symptoms of liver fluke infection can range from fever, nausea to gall bladder inflammation, and bile duct blockage. 

6. Leishmania chagasi and Leishmania donovani

Both of these protozoans are able to cause a dreadful disease called visceral leishmaniasis (also called black fever or kala-azar) in humans. During the infection, the spleen, bone marrow, and liver are affected severely and undergo swelling. Thus, the infected person experiences lowered immunity, and blood cell count that further results in anemia, weight loss, prolonged fever, and various other body problems. 

According to WHO, 95% of the patients who suffer from visceral leishmaniasis, if do not receive timely treatment, succumb to death. Also, there are two more types of leishmaniasis found in humans called mucosal leishmaniasis and cutaneous leishmaniasis, they cause infection in the mucous membrane and skin sores respectively. However, both of these infections are not considered fatal.

5. Filarial worm

The filarial worm (also known as Wuchereria bancrofti) enters the human body through the bite of an infected mosquito. This thread-like worm then attacks the human lymphatic system, eventually causing excessive swelling of legs, external reproductive organs, arms, and breasts, this condition is called elephantiasis or filariasis. In many cases, the infected person becomes permanently disabled because the body is either partially or completely deformed due to abnormal distribution of lymphatic fluid in the affected regions.  

According to the Centres for Disease Control and Prevention (CDC), until now, more than 120 million lives have been affected due to filariasis in different parts of Asia, Africa, and South America. About 40 million people have become permanently disabled due to this infection, and In some backward areas of the world, many such individuals are relegated from society. They are facing discrimination, and are forced to live alone.

4. Plasmodium parasite (malaria)

Ex UNICEF Chief of Health, Stefen S. Peterson famously claimed that every two minutes, a child loses their life to malaria. A press release from UNICEF also reveals that nearly half of the world’s population is at risk of malarial infection, meanwhile, the disease is already killing hundreds of thousands of children every year. A study claims that more than 150 million people have died of malaria in the last 150 years, and the disease accounts for nearly two to five percent of all human deaths.

Malaria is caused by four different species of plasmodium, out of which Plasmodium falciparum causes the most lethal type of malaria. There are three ways by which the Plasmodium parasite can enter your body:

• From the bite of a female anopheles mosquito.
• If a person receives blood from a malaria-infected donor.
• During pregnancy, Plasmodium parasites from an infected mother can infect the child.

Despite being so threatening, malaria is a curable disease and patients can be treated by the use of antibiotics and antiparasitic drugs. However, if you live or travel to a place, which is inhabited by mosquitos, the easiest and most effective way to prevent malaria infection is to use an insecticide-treated bed net. 

3. Acanthamoeba

This amoebic parasite causes granulomatous amoebic encephalitis (GAE), a disease that leads to swelling in the brain. About 95% of the patients who suffer from GAE are killed by the amoeba. However, not every Acanthamoeba infected person suffers from GAE, and some patients may never show any symptoms.

The parasite can be found in soil, chlorinated swimming pools, tap water, on the surface of your contact lenses, bottled water, and air-conditioning units, and it may enter the human body through the eyes, ulcers, wounds, and nasal cavities.

When Acanthamoeba infects the eye, the condition is called keratitis. The infected person faces severe eye pain, blurry vision, redness in the eyes, corneal ulcers, and various other eye-related problems. In such a case, early diagnosis is extremely important because if left untreated, the patient may become permanently blind due to the infection.

2. Toxoplasma gondii

Pregnant women are advised by doctors to stay away from cats because these furry animals are often found to be the carriers of Toxoplasma gondii, a parasite found in cat feces, cat litter boxes, and sometimes also in uncooked meat. While adults may show no symptoms even after Toxoplasma infection due to normal immune response, Toxoplasma gondii is considered life-threatening for human embryos and infants.

The parasite causes congenital toxoplasmosis in the fetus due to which an infant may be born with epilepsy, mental disorders, blindness, etc. In serious cases, it can also lead to miscarriage. Every year, on average, 190,000 children are born with congenital toxoplasmosis, and hundreds of them lose their lives due to the infection. 

1. Brain-eating amoeba

The infection from Naegleria fowleri (the brain-eating amoeba) is both deadly and rare. In the period between 1962 to 2019, only 148 individuals were reported to be infected with this parasite in the US, but of them, only four patients were able to survive the attack. The larvae of Naegleria fowleri are found in soil and warm water bodies such as lakes, swimming pools, and hot springs. 

The parasite enters humans through the nasal cavity, reaches the brain, and starts damaging brain tissues causing a fatal disease called Primary Amebic Meningoencephalitis (PAM). As a result of this, within five to seven days the infected person dies. Researchers believe that the infection generally occurs in humans due to swimming in infected pool water, therefore it is recommended to use nose plugs or clips while you swim.

These are just a few of the world’s most dangerous parasites — the ones that we’ve come across, at least. There are plenty more dreadful ones out there, just waiting to get us. The world can be a dangerous place, be careful.