Benzimidazole Toxicity in Birds
American Association of Zoo Veterinarians Conference 1999
Lauren L. Howard1, BS; Rebecca Papendick2, DVM; Ilse H. Stalis2, DVM; Jack L. Allen3, DVM; Meg Sutherland-Smith4, DVM; Jeffery R. Zuba3, DVM; Daniel Ward5, MS; Bruce A. Rideout2, DVM, PhD
1Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA, USA; 2Department of Pathology, Zoological Society of San Diego, San Diego, CA, USA; 3Department of Veterinary Services, San Diego Wild Animal Park, Escondido, CA, USA; 4Department of Veterinary Services, San Diego Zoo, San Diego, CA, USA; 5Support Laboratory for Study Design and Statistical Analysis, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA, USA
Medical records and necropsy reports of 402 pigeons and doves from the Zoological Society of San Diego were examined to determine if birds treated with fenbendazole (FBZ; Panacur, Hoescht Roussel Agri-Vet Comp, Somerville, NJ, USA) or albendazole (ABZ; Valbazen, Pfizer Animal Health Group, Lee’s Summit, MO, USA) had a higher prevalence of toxicity related signs compared to nontreated birds. Birds presented for non-medical reasons (quarantine, relocation, pre-shipment examinations, and routine parasite screening) were exclusively used to avoid confounding variables involved in comparing sick birds to healthy birds. Compared to 5% average weight gain in nontreated birds, birds given FBZ had an average weight loss of 12% (p=0.0004), and birds given ABZ had an average weight loss of 13.3% (p=0.0028). Percent of birds with marked leukopenia (WBC <1,000/µl) was higher in FBZ treated birds (62.5%) and ABZ treated birds (100%), compared to nontreated birds (2.1%). Bone marrow hypoplasia was found in more FBZ treated birds (33.9%) and ABZ treated birds (83.3%) than nontreated birds (1%). Small intestinal crypt epithelial changes were not found in nontreated birds, but were identified in 24.5% of FBZ treated birds and in 58.3% of ABZ treated birds. Percent survival was lower in FBZ treated birds (50%, p=0.0001) and ABZ treated birds (66.7%, p=0.0001) than in nontreated birds (92.4%). FBZ treated birds also had shorter average survival times following treatment or examination (281.1 days) than nontreated birds (1,231.5 days). FBZ effects appear to be dose related. Birds treated with FBZ at 100 mg/kg showed significantly greater average weight loss (17.7%) and lower survival (11.1%) compared to birds given FBZ at 50 mg/kg, with 7.7% weight loss and 68.4% survival. Birds treated with FBZ at 100 mg/kg also had shorter average survival times following treatment (27 days) than birds treated with FBZ at 50 mg/kg (387 days). These findings are consistent with a toxic etiology. The results of this study suggest that birds of the order Columbiformes are susceptible to toxicity following FBZ or ABZ administration.