2013 Annual Report
1a.Objectives (from AD-416):
Objective 1: Investigate Mycoplasma gallisepticum (MG) genetic differences between field MG isolates and vaccine strains using comparative genomics to determine virulence attributes, pathogenesis, and provide information on similarity between field isolates and vaccine strains. This project focuses on increasing the knowledge associated with MG and MG pathogenesis towards future application of novel means of control. The research will utilize genomic sequence comparisons to identify or characterize virulent factors associated with MG. Sequences to be compared will include MG strains derived from avirulent live attenuated vaccines (LAVs), field isolates (virulent and avirulent), and laboratory strains currently used in experimental disease models. Available MG genomes (n=3) will also be included in the comparisons.
Objective 2: Optimize the strategies for efficacious use of MG vaccines including application protocols, cross-protection between isolates, and dosage; and investigate the transmission risks between field and vaccine isolates including environmental parameters required for organism spread. This project focuses on currently available MG vaccines which are widely used in the table egg industry. While not wholly protective, these vaccines are a primary means of reducing losses associated with virulent field strain outbreaks. This research will investigate strategies to maximize the protection afforded by commercially available MG vaccines. The research will assess the physiological and production effects as affected by route of application, dosage, and the concerted vaccination with an MG bacterin. The persistence of the live attenuated vaccines (LAVs) will also be determined as associated with these factors. Also, as specific LAVs have been demonstrated to be pathogenic to turkeys and meat-type chickens, this research will assess transmission (horizontal and vertical) risks associated with the LAVs. The subobjectives are as follows:
Subobjective 2.1: Effect of application protocols of live attenuated MG vaccines.
Subobjective 2.2: Effects of vaccination protocols and environment on the horizontal transmission of live attenuated MG vaccine strains.
Subobjective 2.3: Assessment of vertical transmission of live attenuated MG vaccines.
Subobjective 2.4: Effect of dosage of F strain-derived live attenuated MG vaccines.
Subobjective 2.5: Effect of overlaying live attenuated MG vaccines on table-egg layers previously vaccinated with an MG bacterin.
1b.Approach (from AD-416):
Genetic differences between Mycoplasma gallisepticum (MG) vaccine strains, field strains, and laboratory strains will be determined by means of comparative genomics. MG genomes originating from various MG strains will be sequenced and compared. Associated findings may be used to identify factors related to MG virulence, further describe the MG pathogenesis, develop novel and specific means of protection, and provide information regarding features common among MG strains. To optimize protection afforded by commercially available MG live attenuated vaccines (LAVs), the effect of application routes and applied dosages will be investigated. LAVs will be applied either by spray and eye drop and at varying dosages above and below those rates recommended by their manufacturers. Vaccination effects will be determined by serology and treatment-associated in vivo MG persistence. Vaccinated subjects will be subsequently challenged by virulent MG and treatment-associated protection will be characterized. The transmissibility of LAVs from subjects vaccinated by spray and eye drop at varying dosages will be determined via in vitro means and by monitoring the MG-status of commonly housed subjects previously demonstrated as MG-free. Transmission of MG will be determined by serological findings and MG detection by culture or molecular means. To assess cross-protection between MG vaccines, subjects will be dually and singly vaccinated with an MG bacterin and MG LAVs and associated effects characterized.
To address the effect of application protocols of live attenuated MG (Mycoplasma gallisepticum) vaccines (LAV), a spray cabinet which permits vaccine application route (eye drop vs. spray) and vaccine deposition (eye, whole body, head-only or body-only (no head) was developed to address subsequent horizontal transmission vaccination. Using this vaccine application cabinet, layer chickens have been vaccinated, and sampling is ongoing to assess vaccination success.
In addressing a separate milestone, in the first of two planned trials, the MG vaccine Mycovac-L™ whether alone or in combination with the killed MG vaccine, MG-Bacterin™, was shown to protect hens already in production from a drop or decrease in egg production subsequent to overlay with the F strain of MG at 45 weeks of age (woa). However, use of a killed MG vaccine, MG-Bacterin™, alone was not able to protect from a drop or decrease in egg production subsequent to overlay with the F strain of MG at 45 woa. This information is important to egg producers, particularly wherein either Mycovac-L™ or MG-Bacterin™ vaccine have been used singly in a layer complex over several generations and the producers desire to use one of the more often preferred F strain MG vaccines. The results show that an F strain MG vaccine can be overlaid onto a flock of layer chickens formerly vaccinated with Mycovac-L™ with no subsequent detrimental impact on egg production; however, in those flocks wherein only MG-Bacterin™ has been used, an overlay with an F strain MG vaccine can be expected to result in a drop or decrease in egg production.
Toward investigating genetic differences between field MG isolates and vaccine strains, 16 MG strains are now in the lab. All strains either have been or are being grown from single colonies to obtain genomic deoxyribonucleic acid (DNA) with minimal in-strain mutational variation. The DNA will be sent for sequencing in the next few weeks.
Purswell, J.L., Evans, J.D., Leigh, S.A., Collier, S.D., Olanrewaju, H.A., Kim, E.J., Pharr, G.T., Peebles, E.D., Branton, S.L. 2012. Mycoplasma gallisepticum transmission: Comparison of commercial F-strain vaccine versus layer complex-derived field strains in a tunnel ventilated house. Poultry Science. 91:3072-3079.