Paromomycin Sulfate Treatment in Histomoniasis Outbreaks in Three Commercial Turkey Flocks in the Fraser Valley of British Columbia, Canada.

Over the last couple of years, the number of histomoniasis cases in commercial turkeys has increased substantially in British Columbia, particularly in the Fraser Valley. Due to a lack of approved efficacious preventive or curative drugs in Canada, histomoniasis outbreaks have had significant economic and animal welfare impacts on the commercial turkey industry. In July 2020, Health Canada conditionally approved the treatment use of paromomycin sulfate on a case-by-case basis via an emergency drug release authorization. Three flocks infected with Histomonas meleagridis were treated with labeled-dose paromomycin sulfate in the feed shortly after presumptive diagnosis. Despite the treatment, two out of three flocks suffered significant losses. One flock suffered over 67% mortality by the eighth day of treatment. Due to significant production loss and animal welfare concerns, the flock was shipped early for mercy cull; thus sustained 100% production loss. Another flock experienced over 38% mortality by the end of the fourth week of treatment and was slaughtered early to minimize production loss. The treatment response in two out of three cases suggests that any curative effect of paromomycin is limited. Thus, future field evaluation should carefully consider the prophylactic use of paromomycin sulfate, especially on farms with recurrent outbreaks.