The following text was automatically extracted from the image on this page using optical character recognition software:
TPDN 1988, Vol. 48, No. 32
INCUBATION PERIOD
The period of time between the initial contact with amebae and clinical symptoms is considered
three to 15 days, with the usual time about seven days.
SIGNS AND SYMPTOMS
PAM is a disease characterized by an abrupt and fulminant course leading almost invariably to
death. The symptoms are associated primarily with severe meningeal irritation and consist of
severe headache, stiff neck, fever (39 C-40 C; 102.20 F-1040 F), and vomiting. Pharyngitis or
symptoms of nasal obstruction and discharge are less frequent. An occasional complaint the
first day or so is a distortion of taste or smell. Headache, vomiting, and fever persist, but
within two to four days after onset, drowsiness, confusion, and neck stiffness develop.
Convulsions may occur but have not been pronounced in most cases. Progressive deterioration
follows, leading to deep coma with minimal if any neurological signs. The vast majority of
cases have ended fatally about one week after the appearance of the first symptoms.
The diagnosis is established by finding trophozoites in the spinal fluid. The peripheral white
cell count is usually elevated with a shift to the left. The spinal fluid is usually purulent
with a preponderance of neutrophils, resembling an acute bacterial infection. The protein
content almost always is markedly elevated in the range of 100 to 1,000 mg/mL. The glucose
content can be normal to mildly reduced. A wet mount of the spinal fluid may demonstrate
motile amebae.
DIFFERENTIAL DIAGNOSIS
No distinct differences exist which will allow differentiation of PAM from acute pyogenic or
bacterial meningoencephalitis on clinical grounds. The history of previous good health and
recent swimming in fresh water should raise the index of suspicion, especially during the hot
summer months. Computed tomographic scans show obliteration of the cisterns surrounding the
midbrain and the subarachnoid space over the hemispheric convexities. Marked enhancement
occurs with administration of intravenous contrast medium.
TREATMENT
Many different therapeutic regimens have been tried for the treatment of acute PAM but, to
date, most have been unsuccessful. One case was treated successfully with a regimen of
AMPHOTERICIN - B intravenously and intrathecally (25-50 mg/kg/day IV, 0.1 mg I/T every other
day). The addition of rifampin, miconazole, and tetracycline have been used, and there is some
evidence of synergism. The possibility of cure depends on early, accurate diagnosis with very
aggressive therapy. If there is a clinic. ' pearl to pass on, it is to have a high degree of
suspicion and do a wet-field examination of the spinal fluid to establish the diagnosis of PAM.
Editorial Note: Human Naegleria infections generally occur during warm weather and following
contact with warm or previously warmed water. In most infections worldwide, the water
contacted had been chlorinated. In the United States, most cases occurred following
summertime activities in fresh water lakes and streams.
The use of chlorine in swimming pools may provide some protection, although the amount of
chlorine necessary to kill Naegleria cysts or trophozoites is the subject of debate in the
literature. Certainly, it will take less chlorine to kill the unprotected trophozoite stage,
whereas, the encysted amoeba, being protected by the reasonably thick and protective cyst wall,
will be able to withstand higher concentrations.3 Some reports indicate that the growth of
Naegleria in swimming pools can be prevented by 0.5 ppm to 1.0 ppm of chlorine. Naegleria
fowleri cysts have been shown to be killed within one hour of contact by 0.5 ppm chlorine,
which can be readily achieved in water supplies or pools. Other reports in the literature
state that chlorine as high as 10.0 ppm failed to clear Naegleria from swimming pools. As
regards control measures, one source indicates that maintaining a salinity of 0.7 v weight per
volume in a swimming pool will prevent the colonization of the pool by Naegleria.
Page 2