Retrospective study of severe outbreaks of Histomonas meleagridis in Dutch turkey flocks from 2010-2015

Abstract

Histomonas meleagridis (H. meleagridis) is a flagellated protozoa and the causative agent of a severe disease, histomonosis, that harms the worldwide turkey industry. It emerged in Europe since the ban on nitroimidiazoles and nitrofurans in 2003. Due to rapid horizontal spread in flocks and severe mortality in affected barns it poses a serious financial threat to the Dutch turkey industry. The aim of this study was to create an overview of possible routes of introduction for H. meleagridis, for 13 individual outbreaks of histomonosis selected by the Turkey Sales Cooperation Holland (BAV) in the years 2010 through 2015, and to create an insight in the course of infection for these outbreaks. Selected farms were visited and a survey was conducted to collect information on possible routes of introduction and quantitative and descriptive data were collected for analysis. No correlation could be demonstrated for possible routes of introduction for H. meleagridis. All the outbreaks affected commercial meat flocks and the most outbreaks occurred in the warmer months from spring until fall. Flock size ranged from 10.500 up to 31.000 animals, comprising of both hens and toms, or just hens or toms. In only one case all the barns were affected, in the other cases multiple barns remained unaffected. Cumulative mortality ratio ranged from 22,96% up to 82,55% with a mean of 52,80%. Daily mortality ratio ranged from 2,16% up to 29,98% with a mean of 9,90%. Animals of affected barns that survived the histomonosis did not differ significantly, in weight and condemnation ratio of net carcass weight, from unaffected turkey flocks. Since multiple factors contribute to the severity of an outbreak there should be a benchmark of data under ‘normal’ conditions for reference. Furthermore, if an outbreak occurs all original data of the entire production period must be preserved to collect as many variables as possible. To elucidate difference in mortality and susceptibility under field conditions, isolates obtained from different outbreaks should be analysed to rule out or confirm a difference in pathogenicity between isolates.