Location: Animal Parasitic Diseases Laboratory
2024 Annual Report
Objectives
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
Approach
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
Under Objective 1. The incidence of histomonosis in turkeys and broiler-breeders is increasing because drugs that were effective against the parasite Histomonas meleagridis have been removed due to safety concerns. Controlling the spread of histomonosis will require a thorough understanding of how the protozoan parasite spreads so rapidly through a flock. Although it is known that infection may initiate after ingestion of the helminth Heterakis gallinarum harboring Histomonas organisms, this route of infection seems insufficient to account for explosive transmission. By combining a cell culture method (to induce formation of Histomonas cyst-like forms) with labeling methods, we found evidence of environmentally-resistant cysts. We stained cell culture material and caecal/liver tissue with antibodies reactive to H. meleagridis or with wheat germ agglutinin (WGA), a lectin that binds chitin, a component of protozoan cell walls. These assays revealed cyst-like structures in cell culture and in tissue from infected
poults. If further studies confirm their identity as cysts, this discovery may help explain the rapid spread of Histomonas in turkeys and point to ways of managing the disease (e.g. litter abatement) to minimize exposure of
birds to the parasite.
Under Objective 2. While immunofluorescence assays are useful, they are time-consuming and require technical expertise to correctly identify the parasite. Molecular-based methods may prove easier to standardize for field sampling.
Developing specific PCR assays for Histomonas meleagridis and Heterakis gallinarum DNA provides rapid means to detect them. Including an internal standard avoids false-negative reactions induced by PCR inhibitors present in litter samples. We applied such methods to a limited number of tissue and litter samples from Histomonaspositive farms, demonstrating their ability to identify the parasite contaminating complex matrices. These PCR assays should prove useful for screening large numbers of tissue and environmental samples for the presence of H. meleagridis and provide confirmatory evidence during routine diagnostic procedures.
Accomplishments