Pathogenicity of Naegleria
Index to Amoebae
A species of parasitic protozoa having both an ameboid and flagellate stage in its life cycle. Infection with this
pathogen produces primary amebic meningoencephalitis [PAM]
Transmission is through water based fluids or the air. [Read sewage sludge, biosolids, effluent, reclaimed
PAM [Primary Amoebic Meningoencephalitis] and GAE [granulomatious amoebic encephalitis] both lead to death
in most cases. Eye infections may lead to blindness.
A few Naegleria species have been shown to be pathogenic in humans and animals most notably N. fowleri. This
amoeba is a facultative pathogen capable of living many generations without infecting a host. Trophozoites are
thought to enter the nose during swimming in warm water and thereafter the brain by locomotion and destruction
of neurons. N. fowleri causes Primary Amoebic Meningoencephalitis (PAM) in man Naegleria fowleri posesses
secreted proteases (Ferrante & Bates, 1988), phospholipases (Fulford et al, 1985; Barbour & Marciano-Cabral,
2001), and pore-forming peptides (Herbst et al, 2002), all of which have been implicated in the pathogenic
process. Although man can act as a host, this occurs so infrequently that we are very unlikely to be the primary
host. This host (if indeed there is one) has not yet been clearly identified, but many other mammals have been
reported to be infected or infectable. These include; mice, cotton rats, squirrels, muskrats (John & Hope, 1990),
guinea pigs (Culbertson et al, 1972), and sheep (Young et al, 1980). Many wild animals (but not all) have
significant titres of Naegleria reactive antibodies suggesting that they come into contact with this group (Kollars &
Wilhelm, 1996). It is possible that the main host are fish as these are frequently found to be parasitized by
Naegleria and other amoebae (especially the gills). Invertebrates too cannot be ruled out as snails, amphibians
and reptiles are also associated with Naegleria (Franke & Mackiewicz, 1982).
As in other amoebae there is a strong correlation between temperature tolerance and pathogenicity of Naegleria
species (Griffin, 1972). Naturally, any amoeba that lives within a human host must be able to survive the normal
37oC and elevation above this that occurs in disease associated fevers. The majority of human PAM cases are
caused by Naegleria fowleri which can grow at temperatures as high as 45oC. N. fowleri and other temperature
tolerant Naegleria sp. multiply in bodies of water both natural and man-made that are warm and most PAM cases
where Naegleria is involved have been caused by swimming or other intimate contact with warm waters (De
Jonckheere & Van de Voorde, 1977). However there have been at least three cases have been documented
where no association with water has been made (Lawande et al, 1979; Sugita et al, 1999; Shenoy et al, 2002).
Naegleria is thought to enter the body through the nose and both pathogenic and non-pathogenic Naegleria has
been isolated from the nasal mucosa of non-infected individuals (Cerva et al, 1973; el-Marhoumy et al, 1988).
Initial signs and symptoms of PAM start 1 to 14 days after infection. These symptoms include headache, fever,
nausea, vomiting, and stiff neck. As the amebae cause more extensive destruction of brain tissue this leads to
confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the
onset of symptoms, the disease progresses rapidly and usually results in death within 3 to 7 days.
Links to history articles