Primary amebic meningoencephalitis (PAM), is a disease of the central nervous system 1, 2. PAM is caused by Naegleria fowleri, a free-living ameba. It is a rare disease* that is almost always fatal; only one person in the U.S. out of 128 has survived infection from 1962 to 2012 3. Signs and symptoms of Naegleria fowleri infection are clinically similar to bacterial meningitis, which lowers the chances of initially diagnosing PAM 3. Humans become infected when water containing Naegleria fowleri enters the nose and the ameba migrates to the brain along the olfactory nerve 2, 3. People do not become infected from drinking contaminated water. Symptoms start 1-7 days (median 5 days) after swimming exposure and people die 1-12 days (median 5.3 days) after symptoms begin. PAM is difficult to detect because the disease progresses rapidly so that diagnosis is usually made after death 1, 2. Signs and symptoms of the infection include:
- Stage 1
- Severe frontal headache
- Stage 2
- Stiff neck
- Altered mental status
The disease is generally fatal 3; among well-documented cases, there are only two known survivors in North America, with one from California and the other from Mexico 4, 5. The California survivor’s condition gradually improved during a one-month hospitalization. The only reported side effect to treatment was a reduction in leg sensation for two months after discharge, which gradually improved. There was also no detection of Naegleria fowleri 3 days post-treatment 4. It has been suggested that the survivor’s strain of Naegleria fowleri may have been less virulent, which contributed to the patient’s recovery. In laboratory experiments, the California survivor's strain did not cause damage to cells as quickly as other strains, suggesting that it is less virulent than strains recovered from other fatal cases 6.
The Mexico survivor’s condition did not begin to improve until 40 hours after hospital admission. On day 22 of admission, there was no abnormality shown in the brain scan and the patient was discharged the next day. The patient was followed up for the next 12 months without any recurrence of disease 5.
Multiple patients have received treatment similar to the California survivor, including amphotericin B, miconazole/fluconazole/ketoconazole, and/or rifampin. Several patients received almost identical treatment to the one PAM survivor but did not survive.
Overall, the outlook for people who get this disease is poor, although early diagnosis and treatment might increase the chances for survival 5.
- Marciano-Cabral F, Cabral G. The immune response to Naegleria fowleri amebae and pathogenesis of infection. FEMS Immunol Med Microbiol. 2007;51:243-59.
- Visvesvara GS. Free-living amebae as opportunistic agents of human disease. [PDF - 13 pages] J Neuroparasitol. 2010;1.
- Yoder JS, Eddy BA, Visvesvara GS, Capewell L, Beach MJ. The epidemiology of primary amoebic meningoencephalitis in the USA, 1962-2008. Epidemiol Infect. 2010;138:968-75.
- Seidel J, Harmatz P, Visvesvara GS, Cohen A, Edwards J, Turner J. Successful treatment of primary amebic meningoencephalitis. New Engl J Med. 1982;306:346-8.
- Vargas-Zepeda J, Gomez-Alcala AV, Vasquez-Morales JA, Licea-Amaya L, De Jonckheere JF, Lores-Villa F. Successful treatment of Naegleria PAM using IV amphotericin B, fluconazole, and rifampin. Arch Med Res. 2005;36:83-6.
- John DT, John RA. Cytopathogenicity of Naegleria fowleri in mammalian cell cultures. Parasitol Res. 1989;76:20-5.
There is no universal definition of a “rare disease” but the U.S. Rare Disease Act of 2002 defined a rare disease as affecting less than 200,000 people in the U.S. and this definition has been adopted by the National Institutes of Health, Office of Rare Diseases.