Direct lateral transmission of Histomonas meleagridis in turkeys.

The lateral transmission of Histomonas meleagridis in turkeys was studied in floor pens without the presence of Heterakis gallinarum. Battery-reared poults (120) were transferred at 2 wk of age to concrete-floored floor pens with fresh pine shavings litter (40/group). One group received no exposure. In other groups, either 10% or 25% of the birds were inoculated per cloaca with cultured H. meleagridis (200,000/bird) and placed in the pens as seeder birds. Inoculated birds died at 10-18 days postinfection (PI) showing typical liver and cecal lesions of histomoniasis. Birds in the high-exposure group died of histomoniasis beginning 16 days PI and continuing to 100% mortality by day 23 PI. Birds in the low-exposure (LE) group died beginning on day 19 PI and continuing through day 31 PI. All but one LE bird alive on day 31 PI had severe liver and cecal lesions of histomoniasis at necropsy. There was no evidence of histomoniasis in unexposed birds. No cecal worms (H. gallinarum) were found at necropsy of dead birds or in unexposed birds at the end of the experiment. Even though H. gallinarum is the only known reservoir for H. meleagridis, these results suggest that lateral transmission of histomoniasis through a flock can occur readily through normal contact between uninfected birds and infected birds and their droppings in the total absence of cecal worms.