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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Animal Parasitic Diseases Laboratory » Research » Research Project #442296

Research Project: Characterization, Prevention, and Mitigation of Histomoniasis in Turkey

Location: Animal Parasitic Diseases Laboratory

2023 Annual Report

Objective 1: Harness genetics, genomics, and electron microscopy to better define the epidemiology of Heterakis and Histomonas to inform mitigation strategies. Component 5: Problem Statement 5A Objective 2: Identify targets for pharmacological, phytochemical, or immunological interventions that could be developed into disease preventives and therapeutics. Component 5: Problem Statement 5A Objective 3: Evaluate mitigation strategies for their potential to prevent horizontal transmission of Histomonas meleagridis in commercial turkeys. Component 5: Problem Statement 5A

We will seek better means to limit the impact of outbreaks by: 1) Testing vaccines for their ability to preventing infection or limiting pathogenesis 2) Enhancing diagnostics and outbreak tracing using genetic tools, 3) Establishing management strategies based on improved understanding of pathogenesis and the parasite life cycle; and 4) Preventing disease by identifying novel pharmaceuticals.

Progress Report
Developed an Histomonas meleagridis horizontal transmission model to support Objective 3 as a means of evaluating mitigation strategies against histomonosis. Extrapolated pharmacological doses from humans or other animal species to turkeys using comparative physiology assessment for inclusion rates for efficacy of FDA-approved antiprotozoal compounds in our H. meleagridis horizontal transmission model. Collected and analyzed by microscopy and using a newly-developed PCR assay vector (e.g. darkling beetles, earthworms) samples from histomonosis outbreaks at commercial turkey operations in Arkansas, Missouri, and Virginia, to support Objective 1 of understanding the epidemiology of histomonosis. As part of Objective 1, studied that the impact of environmental conditions on histomonad morphology and survivability to better understand protozoal biology outside of a vector or host. This included using staining procedures to assess metabolic activity and imaging to monitor histomonad morphology. Preliminary light microscopy indicates a “survival” phenotype different from replicating histomonads. Continued a collaboration with Phoreus Biotech (Kansas City, Missouri) to nanoencapsulate drugs or novel compounds of interest to evaluate in vitro and in vivo antihistomonal activity as outlined in Objective 2. These compounds include methyl jasmonate, phenethyl caffeate, and terfenadine. Initiated a collaboration with the Clemson University to investigate genetic manipulation of H. meleagridis to understand parasite biology and to identify potential targets for recombinant vaccines as outlined in Objective 3. Completed an updated comprehensive review related to historical and currently approved non-imidazole antiprotozoal pharmaceuticals in humans and other animal species that could be candidates for Histomonas meleagridis prevention or treatment. As put forth in Objective 2, evaluated 2 non-imidazole drugs licensed in Japan and the EU and found them to be highly effective in vitro in recent tests. Identified several antiprotozoal pharmacological compounds that may be candidate for reducing in vitro growth of H. meleagridis. Preliminary in vivo experiments indicated that comparatively effective dosages were not refused by birds when incorporated into feed, and these were not apparently toxic. As outlined in Objective 1, developed a microscopic evaluation of methylene blue and calcofluor white dye for enumeration and morphological characterization of the different stages of H. meleagridis. As outlined in Objective 2, carried out in vitro and In vivo evaluation of phytochemical alternatives to control or decrease H. meleagridis propagation. Of several evaluated, one commercially available phytobiotic appears to have some benefit on development of lesions and mortality. As put forth in Objective 1, initiated experiments targeting the effect of dietary inclusion of complex carbohydrates on H. meleagridis transmission in turkey poults using a battery cage horizontal transmission model. As put forth in Objective 1, initiated studies on in vitro evaluation of the impact of cysteine protease inhibitors on histomonad activity in vitro and disease progression in vivo.

1. Developing a horizontal transmission model for Histomonas meleagridis. In vivo testing of anti-histomonal compounds against Histomonas meleagridis infection requires a reproducible model of histomonosis. Moreover, horizontal transmission of H. meleagridis is believed to be the primary way that infection spreads among turkeys raised under commercial housing conditions. University of Arkansas researchers studied different feed formulations and H. meleagridid strains to achieve consistent horizontal transmission of the parasite. This research found that the H. meleagridis PHL isolate in conjunction with a low nutrient density diet gave rise to reproducible horizontal transmission of the parasite among poults. This finding should provide a model for evaluating anti-histomonal compounds against horizontal transmission of H. meleagridis and possibly a therapy against histomonosis.

2. Identifying other Histomonas meleagridis forms that may be involved in outbreaks of histomonosis. Histomonas meleagridis spreads rapidly amongst a turkey flock often leading to > 90% mortality. While ingestion of H. meleagridis-containing Heterakis eggs and cloacal drinking are known to be routes of infection, the rapid rise in infection suggests that other more environmentally-resistant forms exist in litter. Applying microscopy followed by staining methods to assess metabolic activity, University of Arkansas researchers identified a “survival” phenotype that was different in many respects from replicating vegetative histomonads. A PCR assay was developed by ARS researchers in Beltsville, Maryland, and found useful for detecting Histomonas and Heterakis in field samples.