Amoeba Infections That Cause Brain Disease

Free-living amoebas are single-cell organisms that can survive in the environment without any kind of host. Amoebic infections in humans are rare but can cause fatal neurological disease.

Naegleria fowleri is found in collections of warm freshwater throughout the world. It most commonly harms young, previously healthy people who have gone swimming in freshwater. Some infections have also been tied to the use of tap water in Neti pots.

Naegleria has three life stages: cysts, trophozoites and flagellated forms. Trophozoites can penetrate nasal tissues and enter the brain. The result is meningoencephalitis, called primary amebic meningoencephalitis, or PAM. It causes a severe headache, fever, neck stiffness, confusion, nausea, and vomiting. The disease is usually fatal within four to six days due to elevated intracranial pressure.

Naegleria is hard to diagnose and moves quickly, making it difficult to even say with certainty how the disease can best be treated. Some research suggests that the combined use of the antifungal medications amphotericin B and fluconazole along with antibiotics and a corticosteroid. 

Like Naegleria, Acanthamoeba species are found worldwide. Reports have been made of finding this Amoeba in swimming pools, lakes, tap water, sewage, contact lens equipment, dialysis machines, heating, and air conditioning systems, vegetables and more. The amoeba can enter the body through the eyes, nose, or skin wounds.

Unlike Naegleria, Acanthamoeba infections rarely occur in healthy people and instead are usually found in those who are immunocompromised (weakened immune systems). The amoeba usually invades the bloodstream first and then travel up into the brain.

Once in the central nervous system, the amoeba causes slow encephalitis. The first symptoms are usually headache, irritability, nausea, and dizziness. Eventually, the infection can cause sensitivity to light, focal neurological problems, double vision, ataxia, confusion, and seizures. The disease is usually fatal within one to two months after the first symptoms appear.

The best treatment for this disease is uncertain. The Centers for Disease Control and Prevention, or CDC, has an investigational drug called miltefosine that may be tried.

Balamuthia is found in the soil. While exposure is common, infection is very rare. Only about 200 cases of Balamuthia have been reported worldwide. It's thought that infection begins by the amoeba invading the skin or by inhaling airborne cysts through the mouth or nose. Symptoms are very similar to Acanthamoeba infection. Diagnosis is difficult and appropriate treatment uncertain, although the investigational drug miltefosine along with other antifungal and antibiotics may be used.

Sappinia is an amoeba that causes encephalitis, and there is only one single reported case in the world. In this affected person, the amoeba caused a single mass in the temporal lobe. The patient improved after being treated with a combination of drugs, which included antibiotics and antifungal medications. 

These amoeba infections are rare enough to make the news when they occur. It's important to remember that while these infections are serious, the likelihood that an individual will ever experience such an infection is very small. That being said, because the infections are so serious when they occur, it's also important for doctors not to ignore the possibility that their patient may have an amoeba in their central nervous system.