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Avian Dis: Blackhead disease in turkeys: direct transmission of Histomonas meleagridis from bird to bird in a laboratory model.

The spread of Histomonas meleagridis infections through groups of turkeys in the absence of the cecal worm vector (Heterakis gallinarum) was studied in a battery cage model. Battery-reared pours were exposed at 2 weeks of age by commingling with infected birds into cages that had the floor lined with paper. One treatment received no exposure, whereas other birds were commingled with 2, 3, or 4 birds/cage (25%, 37.5%, or 50%) inoculated per cloaca with cultured H meleagridis (200000/bird). Inoculated birds died at 7-13 days post-inoculation (DPI) showing typical liver and cecal lesions of histomoniasis. By 14 DPI, 87.5% of the directly inoculated birds died or had severe lesions of histomoniasis. Turkeys commingled with 2, 3, or 4 infected birds became infected at the rate of 72%, 80%, or 75%, respectively. In another experiment, 2 birds/cage (25%) were inoculated with H meleagridis from culture and allowed to commingle with other birds for 1, 2, 3, or 4 days. Two of 12 (16.7%) birds had minor cecal lesions after contact with inoculated birds for 1 day, but 87.5%-100% became infected if inoculated birds remained in the cage for 2-4 days. Contemporaneous inoculation with cecal coccidia (Eimeria adenoeides) as a predisposing factor in blackhead infections was studied using the model. Turkey poults directly inoculated with H meleagridis were allowed to commingle for 5 days with uninoculated birds that had received inoculation with 0, 103, or 104 sporulated oocysts. The coccidian infection appeared to interfere with transmission of blackhead infection by 7 DPI, as suggested by lessened severity of cecal lesions and a lower percentage of infected birds. These studies confirm that histomoniasis is transmitted readily from directly exposed young turkeys to others in the absence of the cecal worm vector, and that this phenomenon can be reproduced in battery cages as an experimental model.

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Article Details
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Author:McDougald, L.R.; Fuller, L.
Publication:Journal of Avian Medicine and Surgery
Article Type:Reprint
Geographic Code:1USA
Date:Mar 1, 2006
Previous Article:Avian Dis: Public health risk from avian influenza viruses.
Next Article:Avian Dis: Development of a polymerase chain reaction-based in vivo method in the diagnosis of subclinical pigeon circovirus infection.

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