Giardiasis in dairy calves: effects of fenbendazole treatment on intestinal structure and function

Twelve Giardia duodenalis-infected Holstein dairy calves were allocated int o a treatment (n = 6) and placebo group (n = 6) according to pre-study faec al 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 ste rile saline solution. Calves were euthanised 7 days following the initiatio n of treatment and intestinal were collected and prepared for trophozoite q uantitation, histology, electron microscopy, and disaccharidase assays. In all calves treated with fenbendazole, intestinal trophozoites were below de tection limits, while in saline-treated calves, trophozoites were observed in all intestinal segments. Histologically, no significant difference was o bserved between treatment groups with respect to intestinal villus height o r crypt depth. However, a significant decline in the number of intraepithel ial lymphocytes (IEL) was observed in fenbendazole-treated calves when comp ared 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/10 0 enterocytes). In addition, measurements from TEM micrographs demonstrated a significant increase in microvillus surface area in the jejunum of fenbe ndazole-treated calves compared with saline-treated calves (31.2 +/- 10.2 v s. 22.8 +/- 7.6 mum(2)). This increase in microvillus surface area was also associated with an increase in jejunal maltase activity in fenbendazole-tr eated calves compared with calves treated with saline. These results demons trate that fenbendazole is an effective treatment for giardiasis in calves. fenbendazole treatment eliminated Giardia trophozoites from the small inte stine of calves resulting in increased microvillus surface area and greater intestinal enzyme activity. This study also demonstrates that the pathogen esis of giardiasis in calves is similar to that observed in humans and labo ratory animals, and provides further evidence that Giardia is a pathogen of cattle with potential economic importance. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.