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ARS Home » Southeast Area » Mississippi State, Mississippi » Poultry Research » Research » Research Project #432042

Research Project: Transmission, Pathogenesis, and Control of Avian Mycoplasmosis

Location: Poultry Research

2020 Annual Report

1. Compare and characterize the transmissibility of Mycoplasma gallisepticum (MG) (virulent and attenuated vaccine strains) between birds in different commercial types of housing systems. 2. Identify the genetic and phenotypic differences between virulent and attenuated vaccine strains which may aid in developing an assay that will allow the differentiation of infection from vaccination. 3. Investigate the efficacy of in ovo vaccination strategies to protect against disease caused by MG.

To determine the transmissibility of Mycoplasma gallisepticum (MG) under varying conditions relevant to commercial poultry industries, layer chickens will be challenged with virulent and attenuated MG strains and then will be placed among naïve poultry. Transmissibility will be assessed by detection the MG among non-challenged poultry. To determine the impact of housing system on the transmission rates both conventional cage and non-cage systems will be investigated. Further, among conventional cage systems, the ventilation systems will include both still air and tunnel ventilation. Among the non-cage systems, experiments will be designed to compare poultry housed over open pit, deep pit, and flush tank systems to determine any effects on MG transmissibility. To compare genetic and phenotypic differences between virulent and attenuated strains of MG, MG strains will be sequenced and their genome assembled. Further, comparative proteomics will be performed, and all associated findings will be analyzed to elucidate differences which may be applied to future means of MG control. To develop an MG in ovo vaccination protocol and test its’ potential for application towards protection of commercial flocks from MG challenge, experiments will be initially be performed to determine appropriate dosage levels. The effects of the various doses of the MG vaccine on the 18 d embryo will be determined and findings will be applied to the development of a commercially applicable high throughput automated protocol. In addition, chicks derived from the vaccinated eggs will be hatched and assessed for afforded protection.

Progress Report
To strengthen the previous findings, two additional trials were conducted to discern the impact of monochromatic light exposures to the layer hens through 30 weeks of age. The studies were completed, and the findings demonstrated that the light treatments had very little impact on egg size distribution and production, bird stress, and feed efficiency. Research performed to further identify and characterize the proteome and genome of Mycoplasma gallisepticum has continued. To this point, analysis of sequenced genomes identified many differences and similarities between the eight strains that have been analyzed. Two proteins were conserved in the genomes of the vaccine strains but were not found in the virulent or disease-causing strains. However, these proteins were not correlated with the proteomic expression data. Research identified more than 140 proteins that are conserved between the eight sequenced strains. Correlation of the genomic and proteomic data identified expression of 100 of these proteins. Most of these proteins are components required for normal cellular operations, are internal to the cell, and are not exposed to the host immune response. However, 16 of the 100 conserved and expressed proteins are potentially exposed on the cell surface and accessible to the host immune response. These proteins include transport proteins, hypothetical proteins, and fibronectin binding protein, and are being pursued for further vaccine and diagnostic studies. Investigations of in ovo-based delivery platforms for application of commercially available Mycoplasma gallisepticum vaccines demonstrated that the temperature-sensitive MG vaccine was not suitable for delivery via in ovo-based platforms, but in addition to a vaccine previously identified as suitable for in ovo delivery, a second more attenuated strain was shown to be applicable to this delivery method and a high throughput automated commercial delivery protocol was developed.

1. In ovo delivery of Mycoplasma gallisepticum vaccines. Mycoplasma gallisepticum (MG) is a common respiratory pathogen of poultry and can reduce egg production in egg-laying poultry by 10%. Currently, live vaccines against MG are delivered via labor intensive means and can require handling of each bird. To minimize labor inputs and stresses associated with bird handling, ARS researchers in Mississippi State, Mississippi, investigated an in ovo vaccination platform for delivery of the live vaccines. In the in ovo system, the vaccines are delivered via insertion into the egg prior to hatch, thereby negating post-hatch handling events specific for MG vaccine delivery. Research conducted demonstrated that the live MG vaccines could be applied via in ovo platforms which will afford egg layer producers an economic low impact means to apply live vaccines against MG and reduce losses associated with the pathogen.

Review Publications
Elliott, K.C., Branton, S.L., Evans, J.D., Leigh, S.A., Kim, E.J., Olanrewaju, H.A., Pharr, G.T., Pavlidis, H.O., Gerard, P.D., Peebles, E.D. 2020. Growth and humoral immune effects of dietary Original XPC™ in layer pullets challenged with Mycoplasma gallisepticum. Poultry Science. 99(6):3030-3037.