Environmental Engineering Reference
In-Depth Information
Following are key points for laboratory diagnosis of
Cyclospora
(Huang et
al., 1995):
1. To maximize recovery of
Cyclospora
oocysts, first concentrate the
stool specimen by the Formalin-ethyl acetate technique (centrifuge
for 10 minutes at 500×
g
) and then examine a wet mount and/or
stained slide of the sediment.
2.
Cyclospora
oocysts are 8 to 10 µm in diameter (in contrast,
Crypto-
sporidium parvum
oocysts are 4 to 6 µm in diameter).
3. Ultraviolet epifluorescence microscopy is a sensitive technique for
rapidly examining stool sediments for
Cyclospora
oocysts, which
autofluoresce (
Cryptosporidium parvum
oocysts do not). If suspect
oocysts are found, bright-field microscopy can then be used to con-
firm that the structures have the characteristic morphologic features
of
Cyclospora
oocysts (i.e., are nonrefractile spheres that contain
undifferentiated cytoplasm of refractile globules).
4. On a modified acid-fast-stained slide of stool (technique used by most
laboratories),
Cyclospora
oocysts are variably acid fast (i.e., in the same
field, oocysts may be unstained or stained from light pink to deep
red). Unstained oocysts may have a wrinkled appearance; observers
must distinguish oocysts from artifacts that may be acid fast but do
not have the all-important wrinkled morphology of the oocyst wall.
5. Using a modified safranin technique, oocysts uniformly stain a bril-
liant reddish orange if fecal smears are heated in a microwave oven
during staining (Visvesvara et al., 1997). If epifluorescence microscopy
is available, the stained slide can first be examined with this tech-
nique and suspect oocysts reexamined with bright-field microscopy.
6. Although not recommended as an optimal technique for detection
of
Cyclospora
, on a trichrome-stained slide of stool the oocysts appear
as clear, round, and somewhat wrinkled.
Helminths
Drinking water in the United States may transmit the following intestinal
worms (nematodes) (NAS, 1977):
•
Ascaris lumbricoides
(stomach worm)
•
Trichuris trichiura
(whip worm)
•
Ancylostoma duodenale
(hookworm)
•
Necator americanus
(hookworm)
•
Strongyloides stercoralis
(threadworm)
