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Appl. Environ. Microbiol., 08 1996, 2798-2805, Vol 62, No. 8
C Ong, W Moorehead, A Ross and J Isaac-Renton
Two adjacent British Columbia, Canada, watersheds with similar
topographical features were studied. Both the Black Mountain Irrigation
District (BMID) and the Vernon Irrigation District (VID) serve rural
agricultural communities which are active in cattle ranching. The present
study was carried out in five phases, during which a total of 249 surface
water samples were tested in the study watersheds. The aims of these phases
were to determine levels of parasite contamination in raw water samples
collected from the intakes as well as from other sites in each watershed
and to investigate cattle in the watersheds as potential sources of
parasite contamination of surface drinking water supplies. Giardia cysts
were not detected in the raw water samples collected from lake sources at
the headwaters of both watersheds but were found in 100% (70 or 70) of
water samples collected at the BMID intake and 97% (68 of 70) of water
samples collected at the VID intake. Significantly higher levels (P <
0.05) of Giardia cysts were found at the BMID intake (phase 1, 7 to 2,215
cysts per 100 liters; phase 3, 4.6 to 1,880 cysts per 100 liters) when
compared with that of the VID intake (2 to 114 cysts per 100 liters). The
BMID watershed has a more complex system of surface water sources than the
VID watershed. Cattle have access to creeks in the BMID watershed, whereas
access is restricted in the VID watershed. Collection of raw water samples
from a creek upstream and downstream of a cattle ranch in the BMID
watershed showed that the downstream location had significantly higher (P
< 0.05) levels (0.6 to 42.9 cysts per 100 liters and 1.4 to 300.0
oocysts per 100 liters) of both Giardia cysts and Cryptosporidium oocysts
than those of the upstream location (0.5 to 34.4 cysts per 100 liters and
0.5 to 34.4 oocysts per 100 liters). Peak concentrations of both parasites
coincided with calving activity. Fecal samples, collected from cattle in
both watersheds, showed 10% (3 of 30) in the BMID and 50% (5 of 10) in the
VID watersheds to be Giardia positive. No Cryptosporidium-positive fecal
samples were found. Giardia cysts isolated from the BMID watershed were
repeatedly infective to gerbils in contrast to those from the VID
watershed. The 10 BMID drinking water Giardia isolates retrieved into
culture and biotyped showed zymodeme and karyotype heterogeneity. The
differences in patterns of parasite contamination and cattle management
practices contribute to the unique watershed characteristics observed
between two areas which are topographically similar and geographically
adjacent.
Copyright © 1996, American Society for Microbiology
Studies of Giardia spp. and Cryptosporidium spp. in two adjacent watersheds
Department of Pathology and Laboratory Medicine, University of British Columbia, Vancouver, Canada.
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