Page 79 - parasitology for medical and clinical laboratoryprofessionals

Protozoal Microorganisms as Intestinal Parasites 59

Symptoms to survive in environmental conditions that may not be
conducive to life for other organisms due to temperature
The diagnosis of Blastocystosis is arguable because it extremes and drying out because of its thick cyst wall.
has not been proven that symptoms associated with the When ingested, the organisms appear to be able
presence of the organism are valid or are a result of the to survive the high levels of acidic hydrogen chloride
infection. It is argued that many people found to har- in the stomach acid and the other gastric juices such as
bor Blastocystis might have other infectious organisms bile. The cysts are not lysed (destroyed) when placed in
responsible for their symptoms. Blastocystis hominis distilled water, whereas normal cells may rupture in the
organisms are found mostly in asymptomatic people, and low-density water. The cysts have been known to survive
only a few persons diagnosed with the infection actually successfully at room temperature for up to 19 days, indi-
experience any symptoms. Potential symptoms that are cating the form’s strong resistance (Zaman, Howe, and
common complaints from patients infected by B. hominis Ng, 1995; Moe, Singh, Howe, et al. 1996).
are watery diarrhea, abdominal pain or cramps, perianal In another experiment, the cyst form was even able
pruritis (itch), and excessive flatulence. to survive in a liquid culture medium that contained an-
tiprotozoal drugs used for growing bacterial and yeast
Life Cycle cultures. This ability to survive such a restricted envi-
ronment further lends support to the belief that the cyst
The life cycle, along with its questionable pathogenic- form of Blastocystis is the most resistant of the four forms.
ity, appears to not be fully developed. However there are The most likely life cycle begins with ingestion of the
three stages called the amoebic, the cyst, and the central cyst form. After ingestion, the cyst develops into three
body or vacuolated form. The parasite reproduces in the other forms which may in turn redevelop into cyst forms.
same manner as amoebae, by binary fission, or by spo- Through human feces, the cyst forms enter the external
rulation. B. hominis feeds on bacteria and detritus of the environment and are transmitted to humans and other
gastrointestinal tract. animals via the fecal-oral route, repeating the entire cycle.

Disease Transmission Treatment and Prevention
A number of investigators do consider B. hominis to be Treatment for Blastocystis is initiated only when the
at least a possible pathogenic organism. It is assumed organism is detected in significant numbers. The agent,
that the fecal-oral route of transmission is responsible for metronidazole, that is effective against a variety of para-
infections, although this belief is not supported by any sitic pathogens and some bacteria is the predominant
specific characteristics or body of scientific knowledge. drug used for treatment. Iodoquinol is also sometimes
used for treatment when necessary.
Laboratory Diagnosis
ENTAMOEBA HARTMANNI
The cyst form is the more recognizable and more recent
discovery that has helped in the advancement of under- The Entamoeba hartmanni parasite is concentrically
standing the way the infection is transmitted. A perma- round with chromatoid bodies and forms small cysts
nent stained smear using a stain such as the trichrome with four nuclei. It is one of the several parasitic amoe-
stain is most preferred for determining the presence of bae that may be found in the human intestinal tract but is
this organism. Iodine smears, used to identify B. hominis largely considered to be nonpathogenic, but this is an
organisms, are preliminary procedures for a number of issue debated among some professionals. E. hartmanni
other parasites. As compared to the other three forms, is sometimes called a “small-race E. histolytica.”
the cyst is generally smaller in size with a thicker cyst
wall of several layers. It lacks a large central vacuole and Morphology
has a few nuclei, although there are small multiple vacu-
oles and food storage deposits that may be seen. The cyst Entamoeba hartmanni is sometimes called a “small
form is the most resistant form of this parasite and is able E. histolytica” because these two species share a number