Risk of fatal amebic meningoencephalitis from waterborneNaegleria fowleri

Abstract

ABSTRACT/Primary amebic meningoencephalitis (PAM) is a fatal disease of the central nervous system caused primarily by the free-living ameba, Naegleria fowleri. PAM is primarily associated with swimming in various types of fresh water. World literature was reviewed in order to derive a risk analysis model that would be helpful in the management of PAM. The management of PAM risk is difficult, and the prevention of PAM is almost impossible. However, it is reassuring that the cases and risks estimated by the risk model are usually small, with individual annual risk on the order of 10 -6 .Primary amebic meningoencephalitis (PAM) is a fatal disease of the central nervous system caused by free-living amebae that exist in water and soil. Two genera of amebae, Naegleria and Acanthamoeba, are known to cause fatal PAM. There is general agreement that Naegleria fowleri is the most frequent cause of PAM. There is some disagreement as to whether Naegleria gruberi is also pathogenic (Cursons and Brown 1975, DeJonckheere and Van DeVoorde 1976, Duma and others 1971b, John 1982, since Naegleria gruberi can be isolated from healthy people (Shumaker and others 1971). Naegleria fowleri causes a well-defined acutely fatal meningoencephalitis by invading the brain and meninges via the nasal mucosa and olfactory tissue (Anderson and others 1973, Benenson 1985, Carter and others 1981, Chang 1974, Darby and others 1979, Duma 1978, Jamieson and Anderson 1973, Rothrock and Buchsbaum 1980, Wellings 1977c, Willaert and others 1974. Naeglerial PAM is primarily associated with swimming and other water contact activities that allow water into the nasal passages (Cain and others 1979, Cursons and others 1979, Dorsch and others 1983, Jamieson and Anderson 1973, John 1982, Martinez and others 1977.Acanthamoeba species cause a poorly defined PAM that has a subacute or chronic course. These amebae probably reach the central nervous system via a skin lesion. Infection usually occurs in chronically ill or immunosuppressed patients with no history of swimming (Benenson 1985, Carter and others 1981, Hoffman and others 1978, Martinez and others 1977, Rinaldi and others 1979, Tyndall and others 1981. The remainder of this report concerns only Naegleriafowleri.Naeglerial PAM was first recognized in 1965 (Darby and others 1979, John 1982, Wellings, 1977c