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Vol. 48, No. 32
Texas Preventable Disease August 13, 1988
Negleri n C RCUJ LA TVNG fJ
Childhood Chloroquine Posionings.-
Frank Bryant, Jr. MD, FAAFP Robert Bernstein, MD, FACP Wisconsin and Washington
Chairman Commissioner
Texas Board of Health
TEXAS STATE
- Bureau of Disease Control and Epidemiology, DOCUMENTS COLLECTION
1100 West 49th Street, Austin, Texas 78756 (512-458-7455)
79z 7NAEGLERIA AND ACANTHOMOEBA
INTRODUCTION
Free living amebae from two genera, Naegleria and Acanthomoeba, are known to cause disease in
humans and other mammals. A rapidly fatal disease, most often called primary amebic
meningoencephalitis (PAM), usually is caused by the ameboflagellate Naegleria fowleri. This
Naegleria infection occurs mostly in active young people (swimmers) without any recognized
predisposing' condition.
Primary amebic meningoencephalitis was first described in 1966,. but human PAM has been found in
retrospective studies as early as 1937 near Richmond, Virginia. The earliest known example of
human PAM was found in a brain preserved in 1909 in England.
Pathogenic free-living amebae such as Naegleria share with other small free-living amebae a
relatively simple life cycle: a)vegetative trophozoite, feeding mostly on bacteria in nature,
b) a resistant cyst phase, often able to resist dessication indefinitely, -and 'c)- in Naegleria,
a transient flagellate phase. With Naegleria it appears that the flagellate can enter the nose
of a swimmer and rapidly revert to an invasive trophozoite.
Since first being described and to date, approximately '129 cases of PAM have been documented
worldwide; 56 of these cases from the United States.. . In 1987, CDC recorded:'* . 2 cases in
Arizona, 1 in Louisiana, 1 in South Carolina, and 1- in Texas. Case histories and animal
experiments demonstrate a direct route of cranial invasion through the olfactory mucosa and
cribriform plate along the olfactory nerve.
CLINICAL ASPECTS OF FREE-LIVING AMEBIC INFECTIONS1
Primary infection by the ameba, N. fowleri, in humans usually involves the- central nervous
system. The disease process is a primary amebic . meningoencephalitis. PAM. usually occurs in
children and young adults who previously have been in good health. Victims usually have had a
recent history of swimming in heated swimming pools or man-made lakes, or "some contact with mud
or brackish, muddy water. However, cases have been reported with. no apparent water contact.
Sub-clinical infections due to free-living- amebae are . possible in healthy individuals, , with the
protozoa living in the nose and throat. Recent reports2 in the dental literature report
isolation of Naegleria in the dentition and month. It ' is also possible- that ' antibodies and
cell-mediated immunity protect some individuals against acute infections in ordinary
circumstances.
PORTAL OF ENTRY AND PATHOGENESIS
The pathogenic amebas probably enter the nasal cavity by inhalation or aspiration of water
containing the trophozoites or cysts. Inhalation or aspiration of aerosols containing cysts
is another possible source of infection. Respiratory symptoms. may be the result of sub-
clinical infection or hypersensitivity. The olfactory neuro-epithelium is 'then principal route
of invasion, and usual anatomical site of the primary lesion, of PAM due to N. fowleri. The
histopathological characteristics include: 1) destruction of - the olfactory mucosa and
olfactory bulbs and 2) hemorrhagic necrosis of both grey and white matter, with . an - inflammatory
infiltrate consisting of abundant polymorphonuclear leukocytes, 'eosinophils, and few
macrophages. Only trophozoites are found in the lesions.
Texas Department of Health
U 0IF NT UBRARiES 7203