Environmental Engineering Reference
In-Depth Information
domestic animals, including cattle, deer, muskrats, raccoons, foxes, squirrels,
turkeys, pigs, goats, lambs, cats, and dogs and zoonotic transmission to humans
has been documented. The oocyst, 3 to 6
µ
m in diameter, survives 18 months or
longer at 39
◦
F(4
◦
C), however, inactivation can be exacted at 45
◦
C (20 minutes),
64.2
◦
C (5 minutes), 72.4
◦
C (1 minute), and - 20
◦
C(3days).
Conventional rapid sand filtration, including coagulation, should remove 90
to 100 percent of the
Cryptosporidium
. The oocysts may be inactivated in
the presence of a free chlorine residual of 2 mg/l (two days) at 20
◦
C; 2 mg/l
(one day) at 30
◦
C, and 10 mg/l (less than six hours) at either temperature
under chlorine-demand free conditions.
79
Circumstances contributing to the
resistance of oocysts to chlorine in real-world conditions include presence of
chlorine-consuming organic matter, protection of oocysts by clumping, and
protection of oocysts by adsorption to particulate matter. Other chemicals,
such as hydrogen peroxide (6 to 7.5 percent) and ammonia (5 percent), can
be effective. Ultraviolet irradiation presents the interesting effect of being able
to curtail infective capability in oocysts irradiated at low dosage (99 percent
at 1 mWs/cm
2
at 20
◦
C), however, prevention of excystation required 230
mWs/cm
2
at 20
◦
C.
80
Cyclosporiasis is a diarrheal disease with symptoms
closely resembling cryptosporidiosis, including watery diarrhea without blood,
which may last for an extended period of up to 40 days. Other symptoms
are anorexia, nausea, vomiting, pronounced flatulence, stomach cramps, and
abdominal bloating. The incubation period is similar to that of cryptosporidiosis.
The causative agent is
Cyclospora cayetanensis
— an intestinal parasite with
many of the characteristics of
Cryptosporidium
spp. and viewed as an emerging,
opportunistic waterborne pathogen.
In this vein, increased numbers of immunocompromised people in the popu-
lation since the AIDS epidemic appears to be a root to the upwelling of disease
incidence by organisms such as
Cyclospora
sp. and the collection of intracellular
parasites making up the Microsporididea.
81
The oocysts of
C. cayetanensis
are
larger (8 - 10
m in diameter and approximately the size of
Giardia
spp. cysts)
than those of
Cryptosporidium
spp. However, this feature has not deterred much
past misdiagnosis of diseases caused by the misinterpretation of
Cyclospora
sp.
for
Cryptosporidium
spp. One important difference between the cycle of cryp-
tosporidiosis and cyclosporiasis is that the latter is not transmitted person to
person, owing to the need for oocysts of
Cyclospora
sp. to spend an extended
amount of time outside the human host in order to sporulate; a condition essential
for the oocysts to become infectious upon transfer to another human. Detection
of
Cyclospora
sp. oocysts, which autofluoresce a bright blue by epifluorescence
microscopy, involves laboratory techniques similar to those described for
Cryp-
tosporidium
spp.
82
Inactivation of the oocysts of
Cyclospora
sp. is difficult.
Organisms die quickly at - 70
◦
C; at - 20
◦
and - 15
◦
C, survival is one day and
two days, respectively.
Information on the effect of chemical disinfectants on the oocysts of
Cyclospora
sp. is little known. On the one hand, there is the general belief that
oxidants such as chlorine are ineffective, at least at the concentrations employed
µ
