Balamuthia mandrillaris: identification of clinical and environmental isolates using genus-specific PCR.

The protist genus Balamuthia was first described as the causative agent of a fatal case of encephalitis in a mandrill [8]. Originally classified as a leptomyxid ameba, it was eventually given genus status as Balamuthia mandrillaris [8,9]. Since the original isolation, numerous isolates have been found in granulomatous amebic encephalitis (GAE) cases in a number of vertebrates, including humans, almost all of which have been fatal [3–6]. Diagnosis of a Balamuthia infection has been very difficult and the source of the infection is often not identified prior to autopsy examination. Furthermore, until recently, Balamuthia has been difficult to grow in the laboratory in cell-free media [7]. Morphologically, Balamuthia is somewhat similar to Acanthamoeba, however the trophozoite is larger than that of Acanthamoeba. Also, Balamuthia shares the biphasic life style of Acanthamoeba consisting of a mobile trophozoite form, and a resistant cyst form. Despite these similarities, the size difference and unique shape of the trophozoites of Balamuthia make it distinguishable from Acanthamoeba by trained observers using microscopy. Because of the similarities between these two genera, Balamuthia has been hypothesized to share common ecological habitats with Acanthamoeba, including being found naturally in soil. Despite this, until recently isolation of Balamuthia from the environment has been very difficult, if not impossible [7]. The goals of these Balamuthia studies are to determine the phylogenetic placement of Balamuthia relative to other free-living ameba, to determine the levels of genetic variation within isolates of Balamuthia, to develop genus-specific identification methods for Balamuthia, and finally, to apply these genus-specific identification methods to archived and live samples. This will lead to the eventual goal of more rapid and robust identification methods for putative B. mandrillaris opportunistic infections, which continue to increase in frequency and worldwide distribution in an expanding number of vertebrates.