Twelve Giardia duodenalis-infected Holstein dairy calves were allocated into a treatment (n=6) and placebo group (n=6) according to pre-study faecal
cyst counts. Calves in the treatment group received an oral dose of 5 mg/kg
fenbendazole once daily for 3 days, while placebo calves received a sterile
saline solution. Calves were euthanised 7 days following the initiation of treatment and intestinal were collected and prepared for trophozoite quantitation, histology, electron microscopy, and
disaccharidase assays. In all calves treated with
fenbendazole, intestinal trophozoites were below detection limits, while in saline-treated calves, trophozoites were observed in all intestinal segments. Histologically, no significant difference was observed between treatment groups with respect to intestinal villus height or crypt depth. However, a significant decline in the number of intraepithelial lymphocytes (IEL) was observed in
fenbendazole-treated calves when compared with placebo-treated calves in the duodenum (13.9+/-1.2 vs. 17.0+/-1.1 IEL/100 enterocytes) and jejunum (21.6+/-0.8 vs. 30.7+/-1.0 IEL/100 enterocytes). In addition, measurements from TEM micrographs demonstrated a significant increase in microvillus surface area in the jejunum of
fenbendazole-treated calves compared with saline-treated calves (31.2+/-10.2 vs. 22.8+/-7.6 microm(2)). This increase in microvillus surface area was also associated with an increase in jejunal
maltase activity in
fenbendazole-treated calves compared with calves treated with saline. These results demonstrate that
fenbendazole is an effective treatment for
giardiasis in calves.
fenbendazole treatment eliminated Giardia trophozoites from the small intestine of calves resulting in increased microvillus surface area and greater intestinal
enzyme activity. This study also demonstrates that the pathogenesis of
giardiasis in calves is similar to that observed in humans and laboratory animals, and provides further evidence that Giardia is a pathogen of cattle with potential economic importance.