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.