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Amoeba in the Central Nervous System

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Updated April 18, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Free living amoebas are monocellular 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

Naegleria fowleri is found in collections of warm fresh-water 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 a meningitis with headache, fever, neck stiffness, 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 use of amphoteracin B, usually used to treat fungal infections, may be the best approach.

Acanthamoeba

Like Naegleria, Acanthamoeba species are found world-wide. Reports have been made of finding this Amega in swimming pools, sewage, contact lens equipment, dialysis machines, air conditioning cystems, 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 have been immunocompromised. The amoeba usually invade the bloodstream first, and then travel up into the brain.

Once in the central nervous system, the amoeba causes a slow meningoencephalitis and can also cause space-occupying lesions in the brain. The first symptoms are usually headache, irritability, nausea and dizziness. Eventually, the infection can cause focal neurologic 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. A wide array of medications have been tried.

Balamuthia Mandrillaris

Balamuthia is found in soil. While exposure is common, infection is rare. Only about 150 cases of Balamuthia have been reported worldwide. It is thought that infection begins by the amoeba invading hte skin or by inhaling airborn cysts. Symptoms are very similar to Acanthamoeba infection. Diagnosis is difficult and appropriate treatment uncertain.

Sappinia

A case of encephalitis due to this amoeba was described in 2001. The amoeba caused a single mass in the temporal lobe. The patinet improved after being treated with azithromycin, pentamidine, itraconazole and flucytosine.

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

Sources:

Gelman BB, Rauf SJ, Nader R, et al. Amoebic encephalitis due to Sappinia diploidea. JAMA 2001; 285:2450.

Huang ZH, Ferrante A, Carter RF. Serum antibodies to Balamuthia mandrillaris, a free-living amoeba recently demonstrated to cause granulomatous amoebic encephalitis. J Infect Dis 1999; 179:1305.

Schuster FL, Visvesvara GS. Free-living amoebae as opportunistic and non-opportunistic pathogens of humans and animals. Int J Parasitol 2004; 34:1001.

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