CNN
News
Zachary
Reyna, a 12-year-old Florida boy stricken with a brain-eating parasite, has
died. Zachary's family told CNN, believe that the boy who they described as an
active seventh grader was infected while knee boarding with friends in a
water-filled ditch by his house on August 3. Officials warn of brain-eating
amoeba, after he was hospitalized, the boy underwent brain surgery, and doctors
diagnosed him with primary amoebic meningoencephalitis.
The
first symptoms of primary amoebic meningoencephalitis appear one to seven days
after infection, including headache, fever, nausea, vomiting and a stiff neck,
according to the Centers for Disease Control and Prevention. "Later
symptoms include confusion, lack of attention to people and surroundings, loss
of balance, seizures and hallucinations," the agency website says.
"After the start of symptoms, the disease progresses rapidly and usually
cause death within one to 12 days."
Florida
issues warning about rare, brain-eating amoeba
Naegleria fowleri - Brain-Eating
Amoeba
Ravi Kumudesh / Sri Lanka Society for Medical Laboratory Science
Naegleria fowleri,
popularly known as the "brain-eating amoeba", is a free-living excavates
form of protist typically found in warm bodies of fresh water, such as ponds,
lakes, rivers, and hot springs. It is also found in soil, near warm-water
discharges of industrial plants, and unchlorinated or poorly chlorinated
swimming pools in an amoeboid or temporary flagellate stage.
There is no
evidence of this organism living in salt water. It is an amoeba belonging to
the groups Percolozoa or Heterolobosea. N. fowleri can invade and attack the human nervous
system. Although this occurs rarely, such an infection nearly always results in
the death of the victim. The case fatality rate is estimated at 98%.
Signs and Symptoms
Onset symptoms of
infection start about five days (range is from one to seven days) after
exposure. The initial symptoms include, but are not limited to, changes in
taste and smell, headache, fever, nausea, vomiting, and stiff neck. Secondary
symptoms include confusion, hallucinations, lack of attention, ataxia, and
seizures. After the start of symptoms, the disease progresses rapidly over
three to seven days, with death occurring from seven to fourteen days after
exposure.
Causes
In humans, N. fowleri
can invade the central nervous system via the nose. The penetration initially
results in significant necrosis of and hemorrhaging in the olfactory bulbs.
From there, the amoeba climbs along nerve fibers through the floor of the
cranium via the cribriform plate and into the brain. The organism begins to
consume cells of the brain piecemeal by means of a unique sucking apparatus extended
from its cell surface. It then becomes pathogenic, causing primary amoebic meningoencephalitis
(PAM). PAM is a syndrome affecting the central nervous system. PAM usually
occurs in healthy children or young adults with no prior history of immune
compromise who have recently been exposed to bodies of fresh water.
Amphotericin B is
effective against N. fowleri in vitro, but the prognosis remains bleak for those
who contract PAM, and survival remains less than 1%. On the basis of the in
vitro evidence alone, the CDC currently recommends treatment with amphotericin
B for primary amoebic meningoencephalitis, but no evidence supports this
treatment affecting outcome. Treatment combining miconazole, sulfadiazine, and
tetracycline has shown limited success only when administered early in the
course of an infection.
While miltefosine had
therapeutic effects during an in vivo study in mice, chlorpromazine showed to
be the most effective substance the authors concluded: "Chlorpromazine had
the best therapeutic activity against N. fowleri in vitro and in vivo.
Therefore, it may be a more useful therapeutic agent for the treatment of PAM
than amphotericin B.
Untimely diagnoses
remain a very significant impediment to the successful treatment of infection,
as most cases have only been discovered post mortem. Infection killed 121
people in the United States from 1937 through 2007.
Life cycle
Biotic phases:
Naegleria fowleri occurs in three forms:
cyst,
flagellate,
trophozoite
Cyst stage
Trophozoites encyst due
to unfavorable conditions. Factors that induce cyst formation can include food
deprivation, crowding, desiccation, accumulation of waste products, and cold temperatures.
N. fowleri has been found to encyst at temperatures below 10 °C/50F.
Trophozoite stage
The trophozoites are
characterized by a nucleus and a surrounding halo. They travel by pseudopodia,
temporary round processes which fill with granular cytoplasm. The pseudopodia
form at different points along the cell, thus allowing the trophozoite to
change directions. In their free-living state, trophozoites feed on bacteria.
In tissues, they phagocytize red blood cells and white blood cells and destroy
tissue.
Flagellate stage
This biflagellate form
occurs when trophozites are exposed to a change in ionic concentration, such as
placement in distilled water. The transformation of trophozoites to flagellate
form occurs within a few minutes.
Diagnosis
N. fowleri can be grown
in several kinds of liquid axenic media or on non-nutrient agar plates coated
with bacteria. Escherichia coli can be used to overlay the non-nutrient agar
plate and a drop of cerebrospinal fluid sediment is added to it. Plates are
then incubated at 37°C and checked daily for clearing of the agar in thin
tracks, which indicate the trophozoites have fed on the bacteria. Detection in
water is performed by centrifuging a water sample with E. coli added, then
applying the pellet to a non-nutrient agar plate. After several days, the plate
is microscopically inspected and Naegleria cysts are identified by their
morphology. Final confirmation of the species' identity can be performed by
various molecular or biochemical methods.[13] Confirmation of Naegleria
presence can be done by a so-called flagellation test, where the organism is
exposed to a hypotonic environment . Naegleria, in contrast to other amoebae,
differentiates within two hours into the flagellate state. Pathogenicity can be
further confirmed by exposure to high temperature (42 °C): Naegleria fowleri is
able to grow at this temperature, but the nonpathogenic Naegleria gruberi is
not.
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Sri Lanka Society for
Medical Laboratory Science
kumudeshr@gmail.com / 0094773077717
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