Objective—To determine whether fenbendazole
effectively eliminates Giardia organisms from chronically
infected cats that have a concurrent
Cryptosporidium parvum infection.
Animals—16 clinically normal cats.
Procedure—Eight cats with chronic concurrent
Giardia and C parvum infections received fenbendazole
(50 mg/kg, PO, q 24 h) for 5 days (treatmentgroup
cats). Feces from each cat were collected and
processed 3 days weekly for 23 days after treatment.
By use of an immunofluorescent assay for detection
of Giardia lamblia cysts and C parvum oocysts, organism
numbers were counted and scored. Fecal results
from treatment-group cats were compared with
those of 8 untreated cats with Giardia infection but no
C parvum infection (control-group cats).
Results—Four of 8 treatment-group cats had consistently
negative results for Giardia infection after treatment.
These 4 cats had consistently positive results
for C parvum oocysts prior to treatment and consistently
negative results after treatment. One treatment
-group cat had positive results for cysts on all fecal
samples, and 3 treatment-group cats had 1 to 3 negative
results and then resumed shedding large numbers
of cysts; each of these cats had consistently
positive results for C parvum oocysts. When compared
with control-group cats, treatment-group cats
shed less Giardia cysts during week 1 after treatment
but not during week 2.
Conclusions and Clinical Relevance—Administration
of fenbendazole decreases Giardia cyst shedding to
less than detectable numbers in some cats. In our
study, persistent C parvum infection may have been
associated with failure of fenbendazole to eliminate
Giardia infection. (Am J Vet Res 2003;64:1027–1029)