Page 92 - parasitology for medical and clinical laboratoryprofessionals

72 CHAPTER 3

for oocysts, seen microscopically, are commonly used. the duodenum and gallbladder, and the microspiridium
Fluorescent antibody detection methods are now avail- spore is the infective stage.
able, and are considered more sensitive and specific than
microscopic methods. Morphology

Treatment and Prevention The spores are extremely small and vary in size from
1 to 4.5 μm, making them some of the smallest parasites
A number of antiparasitic agents are ineffective against the currently known. It is extremely difficult to differentiate
organism of C. parvum, but those who are immunocom- between the parasite and a cocci-shaped bacterial cells that
petent often are free of symptoms in a short period of time are prevalent in stool specimens due to similar size ranges.
after symptoms appear. Some medications are showing
limited success in AIDS victims. Water treatment plants Symptoms
with filtration procedures and sanitary practices will pre-
Symptoms of sporidiosis are similar to those of cryp-
vent most infections as well as reduce or eliminate runoff
of water from animal pens into water supplies. tosporidiosis. Infants and those who are immuno-
compromised (prevalent in many AIDS victims) are
particularly affected. A self-limiting diarrhea may occur
MICROSPORIDIA in those who have a healthy immune system, and after
a few weeks of incubation, nausea with vomiting, fever,
Spores are oval in shape but are difficult to differentiate
abdominal cramps, loss of appetite, and often watery
from bacteria because they are so small. Identification diarrhea occur. For infants, morbidity and mortality are
of spores in feces is actually possible with a modified
prevalent as well as in immunocompromised individu-
trichrome stain that will stain spores a red color. Three als (the organism is present in many AIDS victims). The
or more organisms of this class are recognized as possible
respiratory tract may become involved, as well as the gas-
pathogens of humans and are difficult to differentiate but trointestinal tract.
only recently have been considered as human parasites.
Hundreds of species of microsporidian parasites have
been isolated from a number of vertebrates, as well as Life Cycle
from a variety of crustaceans and insects. The life cycle for the various species of microsporidia
The importance of microsporidia lies in the fact that begins with a spore with thick protective walls to ward
they are members of the phylum Microspora, are pro- off extreme environmental conditions that might harm
tozoal parasites of animals and insects that are respon- the organism. A polar tube is used to infect the cells of
sible for common diseases of crustaceans and fish, and a host and is characteristic of all microsporidia. A spore
have been found in most other animal groups, including that is ingested is stimulated by the gastrointestinal con-
humans. Microsporidia are obligate, intracellular, spore- ditions to penetrate the cellular cytoplasm of the host.
forming protozoa known to infect almost any class of Sporoplasm is spilled into the host cell and multiplica-
animal. These organisms appear to have evolved perhaps tion begins in the cytoplasm of the host’s cells. A number
hundreds of thousands or even millions of years ago and of cellular divisions occur by binary fission, resulting in
evidence appears to have been discovered in anthropo- spore production (sporogony).
logical samples. As with other similar organisms, those
with compromised immune systems are more vulner- Disease Transmission
able to intestinal infection with Enterocytozoon bieneusi.
Infection with E. bieneusi and the condition is becom- During the process called sporogony the thick cell wall
ing increasingly recognized in patients with AIDS and forms to protect against environmental hazards, aiding
chronic diarrhea where the prevalence is up to a third of in the further spread throughout the host. The organ-
those with these long-term medical conditions affecting isms are excreted in urine and feces where they are able
the immune system. But there is still argument among to infect other hosts. Although microsporidiosis is more
professionals over the pathogenic role of E.bieneusi. common in people with weakened immune systems (i.e.,
Replication takes place within the host’s cells, often in immunocompromised), cases do occur less frequently