The effectiveness of benzimidazole derivatives for the treatment and prevention of histomonosis (blackhead) in turkeys

The benzimidazole derivatives, albendazole and fenbendazole were evaluated for their effectiveness in the treatment and prevention of histomonosis (bl ackhead) in turkeys. Histomonosis was produced in 5 week-old birds by placi ng them on broiler breeder litter known to be contaminated with Heterakis g allinae ova and the protozoan Histomonas meleagridis. In the first trial, a t the onset of confirmed clinical disease, birds were treated orally with m etronidazole, a compound known to be effective against Histomonas, Those re ceiving metronidazole had significantly greater mean body weight gains duri ng the treatment period and the 2 weeks following treatment than untreated controls. Treated birds also had significantly lower caecal and liver lesio n scores. These findings served to validate the method of disease reproduct ion and establish its suitability for testing the benzimidazoles. Similar t rials were conducted to determine the therapeutic value of albendazole at 1 00.0 mg/kg of body weight and fenbendazole at 10.0 mg/kg body weight, admin istered orally twice a day for 5 consecutive days. Under these conditions, both drugs were found to be ineffective as treatments. A final trial was co nducted to assess the prophylactic value of albendazole and fenbendazole ad ministration. At the time of placement on contaminated litter, birds were m edicated as previously described with the exception that treatment was cont inued for 14 consecutive days, the approximate incubation period for histom onosis. The trial was terminated on the 16th day. In the case of both alben dazole and fenbendazole, treatment was associated with a significant increa se in mean body weight gain and lower caecal and liver lesion scores. It is believed that the observed prophylactic effect may be attributed to the de struction of the transport vector e.g., Heterakis larvae, or to direct kill ing of the flagellated form of Histomonas which is normally found in the ca ecal lumen and is considered to be more sensitive to chemotherapeutic agent s than the amoeboid form found in tissues. (C) 1999 Elsevier Science B.V. A ll rights reserved.