92
S.L. Chang
examining the plaques under 10X magnification. As shown in Plate 1 the wild N. gruberi
plaque was packed with well-defined, pearl-like cysts (C), while that formed by the
pathogenic strain showed the majority of the cysts of "ghose cell"-like appearance (D).
These findings indicate that under natural aquatic conditions with bacteria as the
chief, if not sole, supply of food, it would be very difficult for pathogenic strains of
Naegleria to maintain colonies in the midst of overwhelmingly larger numbers of wild
strains. This does not rule out the possibility that under certain conditions, which favour
the survival of the pathogenic, Naegleria may persist in an aquatic environment over a
long period.
PROBABILITY OF EXISTENCE OF HUMAN CARRIERS AND/OR
ANIMAL HOSTS OF PATHOGENIC NAEGLERIA
Very recently we received 12 cultures of free-living amoebae from Dr. George R. Healy
of the Center for Disease Control, Public Health Service. These cultures were isolated on
inorganic agar with A. aerogenes by nasal swabs from children before and after swimming
in lakes. Of significance is that eight of these isolates made after swimming and two made
before swimming have been identified as Naegleria. Attempts will be made to establish
them in cell cultures and test them for pathogenicity in mice. It would be most
interesting if any of these strains of Naegleria should turn out to be pathogenic.
These findings were in contrast to those reported by Wand and Feldman (1967) who
encountered no Naegleria amoebae in their cell cultures prepared with throat swabs. This
difference could be due to either preference of Naegleria amoebae to parasitize the nose
to the throat or a short duration of parasitism by these amoebae.
COMMENTS AND CONCLUSIONS
The findings from this study provide only a few missing pieces of swimming-associated
meningoencephalitis puzzle. They do indicate that this disease entity is caused by a
species of Naegleria which is physiologically and pathologically different from the species
N gruberi commonly found in natural waters and soil. It is logical to hypothesize that the
cytopathic effect of the pathogenic Naegleria is essential to its ability to penetrate the
mucosa in the upper nasal cavity and the cribriform plate to facilitate the cranial invasion.
The isolation of Naegleria amoebae only in some of the Florida lakes is an interesting
fact, but its significance cannot be ascertained without a further study of the presence of
pathogenic strains among these amoebae. Such a study can be made with the methods
described in this report and will be carried out in the near future. It is hoped that similar
studies will be made in other involved areas. In* this connection it is worth noting that Dr.
Lubor Cerva has already initiated such a study at the indoor swimming pool in
Czechoslovakia (Cerva, 1971). He reported the presence of Naegleria amoebae in the
water and in all areas of the swimming pool in contact with the water and failed to isolate
any pathogenic strains of Naegleria in any part of the pool. Since the method
used by Cerva could allow the wild strains of Naegleria to overgrow the
pathogenic individuals which, if present, would be so few in numbers, a
different approach may be necessary to give the latter a chance to be
isolated.
S.L. Chang
examining the plaques under 10X magnification. As shown in Plate 1 the wild N. gruberi
plaque was packed with well-defined, pearl-like cysts (C), while that formed by the
pathogenic strain showed the majority of the cysts of "ghose cell"-like appearance (D).
These findings indicate that under natural aquatic conditions with bacteria as the
chief, if not sole, supply of food, it would be very difficult for pathogenic strains of
Naegleria to maintain colonies in the midst of overwhelmingly larger numbers of wild
strains. This does not rule out the possibility that under certain conditions, which favour
the survival of the pathogenic, Naegleria may persist in an aquatic environment over a
long period.
PROBABILITY OF EXISTENCE OF HUMAN CARRIERS AND/OR
ANIMAL HOSTS OF PATHOGENIC NAEGLERIA
Very recently we received 12 cultures of free-living amoebae from Dr. George R. Healy
of the Center for Disease Control, Public Health Service. These cultures were isolated on
inorganic agar with A. aerogenes by nasal swabs from children before and after swimming
in lakes. Of significance is that eight of these isolates made after swimming and two made
before swimming have been identified as Naegleria. Attempts will be made to establish
them in cell cultures and test them for pathogenicity in mice. It would be most
interesting if any of these strains of Naegleria should turn out to be pathogenic.
These findings were in contrast to those reported by Wand and Feldman (1967) who
encountered no Naegleria amoebae in their cell cultures prepared with throat swabs. This
difference could be due to either preference of Naegleria amoebae to parasitize the nose
to the throat or a short duration of parasitism by these amoebae.
COMMENTS AND CONCLUSIONS
The findings from this study provide only a few missing pieces of swimming-associated
meningoencephalitis puzzle. They do indicate that this disease entity is caused by a
species of Naegleria which is physiologically and pathologically different from the species
N gruberi commonly found in natural waters and soil. It is logical to hypothesize that the
cytopathic effect of the pathogenic Naegleria is essential to its ability to penetrate the
mucosa in the upper nasal cavity and the cribriform plate to facilitate the cranial invasion.
The isolation of Naegleria amoebae only in some of the Florida lakes is an interesting
fact, but its significance cannot be ascertained without a further study of the presence of
pathogenic strains among these amoebae. Such a study can be made with the methods
described in this report and will be carried out in the near future. It is hoped that similar
studies will be made in other involved areas. In* this connection it is worth noting that Dr.
Lubor Cerva has already initiated such a study at the indoor swimming pool in
Czechoslovakia (Cerva, 1971). He reported the presence of Naegleria amoebae in the
water and in all areas of the swimming pool in contact with the water and failed to isolate
any pathogenic strains of Naegleria in any part of the pool. Since the method
used by Cerva could allow the wild strains of Naegleria to overgrow the
pathogenic individuals which, if present, would be so few in numbers, a
different approach may be necessary to give the latter a chance to be
isolated.