Naegleria fowleri, Entamoeba gingivalis ,Acanthamoeba species

entamoeba gingivalis
trophozoites.
the trophozoite of entamoeba gingivalis ranges in size from 8 to 20 ?m and morphologically resembles that of e. histolytica (fig. 3-18 table 3-13). e. gingivalis trophozoites characteristically exhibit active motility. the multiple pseudopods vary in their appearance as the trophozoite moves. the pseudopods may appear long when seen at one point in time and short and blunt the next time that they are seen the single nucleus contains a central karyosome surrounded by peripheral chromatin that is for the most part fine and evenly distributed. achromatic granules arranged in strands may be visible extending from the karyosome to the peripheral chromatin ring.
a number of inclusions are typically found in the finely granular cytoplasm including food vacuoles containing phagocytosed and partially digested white blood cells (leukocytes and epithelial cells of the host, bacteria and ingested red blood cells, although not as commonly found as in e. histolytica trophozoites .it is important to note that e. gingivalis is the only ameba that ingests white blood cells. this distinguishing characteristic is helpful when it is necessary to differentiate e. gingivalis from e. histolytica.
cysts.
there is no known cyst stage of e .gingivalis .
laboratory diagnosis
an accurate diagnosis of e. gingivalis trophozoites may best be made by examining mouth scrapings , particularly from the gingival area. material from the tonsillar crypts and pulmonary abscess, as well as sputum, may also be examined. vaginal and cervical material may be examined to diagnose e. gingivalis in the vaginal and cervical areas.

table 3-13 entamoeba gingivalis trophozoite : typical characteristics at a glance
parameter
size range

motility


number of nuclei
karyosome
peripheral chromatin

cytoplasm

cytoplasmic inclusions
description
8-20 ?m

active, varying pseudopod appearance

one

centrally
located fine and evenly distributed.
finely granular

leukocytes epithelial cells bacteria



life cycle
e. gingivalis, as the name implies, typically lives around the gum line of the teeth in the tartar and gingival pockets of unhealthy mouths. in addition, e. gingivalis trophozoites have been known to inhabit tonsillar crypts and bronchial mucus. it is particularly important to diagnose e. gingivalis and e. histolytica correctly because both organisms may be found in the sputum and in pulmonary abscesses.
e. gingivalis may also be found in the mouths of individuals who practice good oral hygiene. existing as a scavenger the e. gingivalis trophozoites feed on disintegrated cells and multiply by binary fission .characteristically delicate, these trophozoites will not survive following contact with stomach juices. e. gingivalis trophozoites have also been recovered in vaginal and cervical specimens from women who are using intrauterine devices (iuds). spontaneous disappearance of the trophozoites seems to occur following removal of the iud.
epidemiology
e. gingivalis is found in all populations that have been studied for its presence. infections of e .gingivalis are contracted via mouth-to-mouth )kissing) and dropinglet contamination , which may be transmitted through contaminated drinking utensils.
clinical symptoms
infections of e. gingivalis occurring in the mouth and in the genital tract typically produce no symptoms. pathogenic e. gingivalis trophozoites are frequently recovered in patients suffering from pyorrhea alveolaris. it appears that the trophozoites thrive under disease conditions but do not produce symptoms of their own.
treatment
treatment of e. gingivalis is typically ( metronidazole) indicated because the organism is generally considered a pathogen .
prevention and control
improved oral hygiene accomplished by the proper care of the teeth and gums is necessary to prevent the spread of oral e. gingivalis infections .prompt removal of iuds in infected patients spontaneously removes e. gingivalis from the genital tract.


- naegleria fowleri
common associated disease or condition name : primary amebic meningoencephalitis (pam).
morphology
naegleria fowleri is the only ameba with three known morphologic forms—ameboid trophozoites , flagellate forms (pertains to protozoa that move by means of flagella), and cysts.
ameboid trophozoites. -1
the typical ameboid trophozoite of n. fowleri appears elongate, measuring from 8 to 22 ?m in length (fig. 3-19 table 3-14). the anterior end is usually broad whereas the posterior end is usually tapered. the sluglike motility of the n. fowleri ameboid trophozoite is accomplished by blunt pseudopodia . the single nucleus contains a large karyosome that is generally centrally located . peripheral chromatin is absent. the cytoplasm of the n . fowleri ameboid trophozoite is granular and often contains vacuoles.
flagellate forms. -2
the pear-shaped flagellate form of n. fowleri typically measures 7 to 15 ?m in size (fig. 3-20). two whiplike structures that assist select parasites in locomotion known as flagella extend from the broad end of the organism . the typical motility that is seen is accomplished by jerky movements or spinning. the nucleus is basically identical to that of the ameboid trophozoite, a large central karyosome minus peripheral chromatin. the flagellate trophozoites typically have granular cytoplasms that often contain vacuoles.





table 3-14 naegleria fowleri ameboid trophozoite: typical characteristics at a glance
parameter description
size range
motility
number of nuclei
karyosome

peripheral chromatin
cytoplasm
8-22 ?m
sluglike, blunt pseudopods
one
large and usually centrally located

absent
granular, usually
vacuolated

3- cysts.
the cysts, measuring from 9 to 12 ?m in size, are generally round and have thick cell walls (fig. 3-21). similar to both corresponding trophozoite stages, the n. fowleri cyst has only one nucleus, consisting of a large, centrally located karyosome lacking peripheral chromatin . the cytoplasm is typically granular and often contains vacuoles.
laboratory diagnosis
microscopic examination of cerebrospinal fluid (csf) is the method of choice for the recoveryof n. fowleri ameboid trophozoites. preparing and scanning saline and iodine wet preparations of the csf are recommended , samples of tissues and nasal discharge may also be examined. clinical specimens may be cultured. n. fowleri ameboid trophozoites show a characteristic trailing effect when placed on agar plates that have been previously inoculated with gram-negative bacilli.
life cycle
the ameboid trophozoites of n. fowleri are the only form known to exist in humans. replication of the ameboid trophozoites occurs by simple binary fission. the ameboid trophozoites transform into flagellate trophozoites in vitro after being transferred to water from a tissue or culture. the flagellate trophozoites do not divide but rather lose their flagella and convert back into the ameboid form, in which reproduction resumes. the cyst form is known to exist only in the external environment , it appears that the entire life cycle of n. fowleri, which consists of the amebic trophozoites converting to cysts and flagellates and then back to amebic trophozoites, occurs in the external environment. humans primarily contract this ameba by swimming in contaminated water. the ameboid trophozoites enter the human body through the nasal mucosa and often migrate to the brain, causing rapid tissue destruction. some infections may be caused by inhaling dust infected with n. fowleri.
epidemiology
n. fowleri is primarily found in warm bodies of water, including lakes, streams, ponds, and swimming pools. prevalence is higher in the summer months of the year. in addition to water sources , there have been cases of contaminated dust. one such case occurred in nigeria, a country that has a warm climate . the ameboid trophozoites of n. fowleri enter the human body through the nasal mucosa. inhalation of contaminated dust has accounted for other documented infections. there is also some evidence to suggest that sniffing contaminated water may transmit this ameba
clinical symptoms
asymptomatic. patients who contract n.fowleri resulting in colonization of the nasal passages are usually asymptomatic . primary amebic meningoencephalitis. primary amebic meningoencephalitis (pam) occurs when the ameboid trophozoites of n. fowleri invade the brain, causing rapid tissue destruction patients may initially complain of fever, headache , sore throat, nausea, and vomiting. symptoms of meningitis rapidly follow, including stiff neck and seizures. in addition, the patient will often experience smell and taste alterations blocked nose, and kernig’s sign (defined as a diagnostic sign for meningitis, where the patient is unable to fully straighten his or her leg when the hip is flexed at 90 degrees because of hamstring stiffness). in untreated patients death usually occurs 3 to 6 days after onset postmortem brain tissue samples of these patients reveal the typical ameboid trophozoites of n .fowleri
treatment
unfortunately, medications used to treat meningitis and amebic infections are ineffective against n. fowleri. there is evidence, however, that prompt and aggressive treatment with amphotericin b may be of benefit to patients suffering from infections with n. fowleri, despite its known toxicity. in rare cases, amphotericin b in combination with rifampin or miconazole has also proved to be an effective treatment. amphotericin b and miconazole damage the cell wall of naegleria, inhibiting the biosynthesis of ergosterol and resulting in increased membrane permeability which causes nutrients to leak out of the cells. rifampicin inhibits rna synthesis in the amoeba by binding to beta subunits of dna dependent rna polymerase, which in turn blocks rna transcription. a person can survive if signs are recognized early but, if not, pam almost always results in death..