AGENT & HISTORY

Agent

Twenty-four species and many different strains of Naegleria have been identified.N. fowleri is the only species known to cause human disease and is the primary cause of primary amebic meningoencephalitis (PAM). Another species, N. australiensis, is known to cause disease in mice, but no cases of human infection have been reported.

History

Study of the genus Naegleria began in 1899, when Shardinger first described an amoeba that could convert into a flagellate and named it "Amoeba gruberi." The genus was also described as Dimastigamoeba, based on the typical morphology of two flagella, before Alexeieff named it Naegleria in 1912. Up until about 1970, however, research focused on how the amoeba converted into the flagellate form, until the pathogenicity of some species of Naegleria was discovered.

The first known case of N. fowleri causing disease in humans was in a patient in Virginia in 1937, but this case was not recognized as N. fowleri until a review of autopsies by Dos Santos in 1968. Literature on N. fowleri dates back to 1965, when Fowler and Carter described 4 patients in Australia suffering from CNS disease. When this paper was published, however, the pathogenicity of N. fowleri was not known, so the authors incorrectly attributed it to opportunistic free-living amoeba of the genus Acanthamoeba. A year later, Butt described a similar disease in a patient in the United States and named the disease, primary amebic meningoencephalitis (PAM). In 1970, further study by Carter revealed that these infections were due to a species of Naegleria, which Carter then named fowleri in recognition of Fowler.

Since then, about 300 cases of primary amebic meningoencephalitis have been reported. Although the incidence has been rare, it is likely underreported and misdiagnosed. Many of the reported cases were not diagnosed until autopsy. Most of the cases have been described in developed countries, but this also likely reflects underreporting in other areas.