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10 Appalling Protozoans You Don’t Want to Encounter

by Jessica Fleming-Montoya
fact checked by Darci Heikkinen

Some diseases, like the flu, although unpleasant, aren’t going to do much more than leave you feeling a little under the weather. However, there are some much more sinister bugs that can have horrifying consequences if you wind up catching them. Many of these diseases are caused by nasty protozoans and amoebas, or single-celled parasites. Here are 10 appalling protozoans you wouldn’t want to catch.

Related: Top 10 Creepiest-Looking Fungi

10 Acanthamoeba

Parasite Invades Eye

Acanthamoeba is an amoeba that lives in freshwater, brackish water, pools and hot tubs, HVAC systems, soil, and dust. In other words, this is an amoeba that gets around.

The amoeba can get picked up through wounds or by entering infected waters, and once it’s in your body, it makes its way into the bloodstream. From there, acanthamoeba can either cause keratitis, a nasty eye infection, or granulomatous encephalitis, an infection of the spinal cord and brain.

Although keratitis is pretty easily treatable, brain and spinal cord infections aren’t. Instead, people usually start displaying symptoms of confusion, lack of attention, loss of motion control, seizures, and hallucinations, which progressively worsen as the infection progresses. Eventually, this infection leads to death.[1]

9 Balamuthia mandrillaris

Family Raises Awareness About Rare, Deadly Brain-Eating Amoeba that Killed Newlywed

Balamuthia mandrillaris is an amoeba that lives in soil, and it’s easily picked up by people breathing near the area where the amoeba is present. However, it can also enter the body through open cuts or sores.

B. mandrillaris is much more common in temperate parts of the world, and if you’re unlucky enough to catch it, your symptoms will probably be pretty mild at first. Initially, all you’ll have to worry about are vomiting, lethargy, and a fever. However, if the disease progresses, it can lead to far worse things. These advanced symptoms involve issues with mental health, seizures, trouble speaking, and even paralysis.

Probably the worst part of this disease, however, is that there’s not a whole lot that you can do about it. Sometimes, symptoms won’t show themselves for months, and when they do, it’s too late to do anything.

Although there are medications available to help treat the disease, doctors usually only figure out what’s going on right before the patient dies. As a result, even if they administer medication, it’s generally ineffective.[2]

8 Entamoeba histolytica

Amoebic dysentery – Entamoeba Histolytica

Entamoeba histolytica causes a disease called amoebiasis, or amoebic dysentery. This nasty parasite infects both humans and animals and kills several thousand people each year.

In general, people contract this disease by touching feces or anything that’s been in contact with feces. Although that sounds hard to do since it can spread through animal feces, too, all you’d have to do is pick up your pup’s poop one day to put yourself at risk.

Once a person has contracted amoebiasis, it takes about ten days for symptoms to start showing up. Common symptoms include fever, nausea, and diarrhea. Besides these more minor symptoms, E. histolytica can also cause abscesses to develop in the liver, lungs, and even the brain.

For those who are unfortunate enough to catch this disease, there is some hope of getting better. Doctors can usually treat the disease with one or two antibiotics, depending on the severity of the infection.[3]

7 Leishmania

Leishmaniasis – Plain and Simple

Leishmania is a parasite that spreads through sandfly bites, which can occur in the tropics or even in parts of Europe. In other words, unfortunately, this is a more common disease than some of the others on this list.

Leishmania causes leishmaniasis, which leads to lesions on your body. Although these sores on your skin won’t do much more than be a bit of a nuisance, you can also develop sores inside your body. These internal sores affect your organs and can lead to some life-threatening complications.

To make matters worse, there aren’t a whole lot of treatments available at the moment. If you want to get rid of leishmania, you’ll be limited to just two different FDA-approved drugs to treat it—amphotericin B and miltefosine. And, in order to diagnose the disease in the first place, you’ll be put through a rigorous round of bone marrow and blood testing.

So it’s safe to say that this is one parasite that it’s best to just steer clear of rather than trying to treat it after the fact.[4]

6 Plasmodium falciparum

Why We Stopped Making Progress on Malaria

Plasmodium falciparum is one of four different types of protozoans that causes malaria, an infection of the red blood cells. Malaria is usually spread through mosquitos, which means it’s far more common in tropical regions where mosquito counts are high.

Malaria starts by shaking you with fever and chills and gradually leads to more severe symptoms such as coma, kidney failure, and seizures.

Although malaria used to cause death in most cases, today, modern medicine means we have pills to treat this disease. There are also preventative pills you can take to keep you from getting it in the first place. So even if you’re heading to the tropics sometime soon, you’re most likely safe from this nasty bug.[5]

5 Cyclospora cayetanensis

Cyclosporiasis outbreak in Texas

No one likes a case of the runs, but if you catch Cyclospora cayetanensis, that’s exactly what you’ve got in store. C. cayetanensis causes something called cyclosporiasis, a disease that leads to gas, diarrhea, nausea, and stomach cramps.

Most people catch this disease by drinking contaminated water—just one more good reason to always stick to bottled water while traveling!

Although this disease won’t kill you, it can last for months at a time. In other words, you could be dealing with loose poop for weeks on end—yuck! Even if you don’t get medical treatment, however, this disease usually clears up on its own, although it can leave you with lingering fatigue and loss of appetite—and maybe fewer friends.[6]

4 Toxoplasma gondii

How cats manipulate your brain with parasites

Most people love snuggling and kissing their cats, but perhaps they should think twice before doing so. That’s because a nasty protozoan called Toxoplasma gondii lives inside cat feces and can infect humans, causing some disastrous results.

If these bugs get into humans, it can lead to toxoplasmosis, which causes flu-like symptoms. However, it can also lead to an increased risk of schizophrenia as well as brain swelling and even blindness!

Despite these horrifying effects, many cases of toxoplasmosis go away on their own. If your symptoms persist for a while, however, you may need medical intervention to prevent something more sinister, like a seizure, from developing.[7]

3 Giardia duodenalis

Wilderness Medicine: Giardia

Giardia duodenalis is a rather nasty protozoan that causes something called “beaver fever.” Beaver fever, or giardiasis, gets picked up when people ingest the protozoan, which lives in feces, food, and contaminated water.

Once you get the disease, you’re likely to start dealing with issues like diarrhea and weight loss. Some people even become lactose intolerant as a result of the infection.

Although this is an unpleasant bug to catch, it’s one that you can treat fairly easily. If doctors find you’ve got a case of giardiasis, they’ll usually give you tinidazole or metronidazole to get you feeling better again.[8]

2 Naegleria fowleri

Brain Eating Amoeba (Naegleria fowleri)

One of the scariest amoebas out there is Naegleria fowleri, a nasty amoeba that lives in warm, shallow bodies of water. This amoeba usually eats bacteria, but if given the opportunity, it will also feed on neurons and astrocytes, or brain cells.

The way this nasty amoeba harms humans is by swimming up your nose. From there, it makes its way to the brain, where it starts to chomp away on your neurons and brain cells. Because of this, it’s often called the brain-eating amoeba.

What’s particularly nasty about this amoeba is that it takes around five days for symptoms to appear. Once they do, then it’s often too late to do anything.

The good news about this amoeba, however, is that it’s not contagious, and it can’t do any harm if it’s swallowed. However, to make sure it doesn’t get up your nose, it’s best just to keep your nose above water next time you’re swimming in the wild.[9]

1 Entamoeba gingivalis

The Risks Of Oral Amoeba – Entamoeba Gingivalis

If you hate visiting the dentist, then Entamoeba gingivalis is probably one amoeba you want to avoid at all costs. This amoeba is found inside the biofilm at the base of your teeth as well as in periodontal pockets.

Now, while there’s some debate among scientists as to whether E. gingivalis causes issues in your mouth or it’s more of an effect, what we can say for sure is that it almost always appears in the mouths of people with gum disease. On the other hand, people with healthy gums don’t usually have this amoeba present.

Entamoeba gingivalis is usually spread by direct contact, such as sharing toothbrushes or kissing. These nasty amoebas move pretty quickly and, if left unchecked, can lead to periodontitis.

The good news is that you can treat this amoeba by getting rid of the biofilm. So while it’s certainly one that can wreak havoc on your mouth, it’s also one that’s relatively easy to cure.[10]

fact checked by Darci Heikkinen