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Published on: February 20, 2015
Experimental infection of chickens and turkeys with Mycoplasma gallisepticum reference strain S6 and North Carolina
B Sanei1, H J Barnes, J P Vaillancourt
1Department of Population Health and Pathobiology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA.
Abstract:
During an epidemic of mycoplasmosis in chicken and turkey flocks in North Carolina between 1999 and 2001, isolates of Mycoplasma gallisepticum (MG) from affected flocks were characterized by random amplification of polymorphic DNA (RAPD), and eight distinct RAPD types were identified. MG RAPD type B accounted for more than 90% of the isolates and was associated with moderate-to-severe clinical signs and mortality. The virulence of MG RAPD type B for chickens and turkeys was compared with sham-inoculated negative controls and MG S6 (a virulent strain)-inoculated positive controls. Clinical signs occurred in chickens and turkeys inoculated with either MG RAPD type B or MG S6. However, they were not as frequent or severe as those seen in naturally affected flocks, and there was no mortality in the experimental groups. Based on gross and microscopic findings, MG RAPD type B was equal to or more virulent than MG S6. All MG-inoculated birds were culture and PCR positive at 7 and 14 days postinoculation (PI). Among serological tests, the serum plate agglutination test was positive for the majority of chickens and turkeys (58%-100%) infected with either strain of MG at both 7 and 14 days PI. The hemagglutination inhibition test was negative for all birds at 7 days PI and positive for a few chickens (8%-17%) and several turkey sera (40%-60%) at 14 days PI. Only a single serum was positive by enzyme-linked immunosorbent assay (an MG S6-infected turkey) at 14 days PI.
Insights
Mycoplasma gallisepticum (MG) type B, prevalent during a 1999-2001 epidemic, showed significant virulence in chickens and turkeys. This study characterized MG strains and evaluated diagnostic test efficacy.
Area of Science:
- Veterinary Microbiology
- Avian Pathology
- Molecular Epidemiology
Background:
- Mycoplasmosis, caused by Mycoplasma gallisepticum (MG), is a significant respiratory disease in poultry.
- An epidemic of MG occurred in North Carolina chicken and turkey flocks between 1999 and 2001.
- Characterization of MG isolates is crucial for understanding disease dynamics and virulence.
Purpose of the Study:
- To characterize Mycoplasma gallisepticum (MG) isolates from an epidemic using random amplification of polymorphic DNA (RAPD).
- To compare the virulence of a predominant MG RAPD type (type B) with a known virulent strain (MG S6) in chickens and turkeys.
- To evaluate the diagnostic performance of serological tests for MG infection.
Main Methods:
- Random Amplification of Polymorphic DNA (RAPD) was used to identify distinct MG types.
- Experimental inoculation of chickens and turkeys with MG RAPD type B and MG S6 strains.
- Gross and microscopic pathological examinations were performed.
- Culture, PCR, Serum Plate Agglutination (SPA), Hemagglutination Inhibition (HI), and Enzyme-Linked Immunosorbent Assay (ELISA) were used for diagnosis.
Main Results:
- Eight distinct MG RAPD types were identified, with type B accounting for over 90% of isolates and associated with severe disease.
- Experimental inoculation with MG RAPD type B and MG S6 caused clinical signs but no mortality.
- MG RAPD type B demonstrated equal or greater virulence than MG S6 based on pathological findings.
- Culture and PCR confirmed MG infection at 7 and 14 days post-inoculation.
- Serum Plate Agglutination (SPA) showed high sensitivity (58%-100%) at 7 and 14 days PI.
- Hemagglutination Inhibition (HI) test showed variable sensitivity (8%-60%) at 14 days PI.
- ELISA showed very low sensitivity in this experimental setting.
Conclusions:
- MG RAPD type B was the predominant and virulent strain during the 1999-2001 North Carolina epidemic.
- Experimental models confirmed the virulence of MG RAPD type B, though less severe than field cases.
- SPA is a sensitive serological test for detecting MG infection early.
- HI and ELISA showed limited utility in this specific experimental context for early detection.
