Antigenic, morphologic, and molecular characterization of new Ehrlichia risticii isolates

Area of Science:

• Veterinary Microbiology
• Infectious Diseases
• Molecular Biology

Background:

• Ehrlichia risticii is the causative agent of Potomac horse fever, an acute infectious disease in horses.
• Understanding the biological diversity of E. risticii is crucial for disease management and diagnosis.

Purpose of the Study:

• To investigate the biological diversity among recent Ehrlichia risticii isolates from horses in Ohio and Kentucky.
• To compare these recent isolates with older strains from Maryland, Illinois, and Virginia.

Main Methods:

• Morphological analysis of E. risticii isolates within P388D1 cells, observing morulae formation.
• Western blot (immunoblot) analysis using polyclonal anti-E. risticii sera to assess antigenic protein profiles.
• Indirect fluorescent antibody labeling with monoclonal antibodies to evaluate antigenic distinctness.
• PCR amplification and AvaII restriction enzyme digestion of the 16S rRNA gene to analyze genetic variation.

Main Results:

• Seven of nine recent isolates formed large morulae, while others, including older isolates, showed dispersed or small morulae.
• Western blot analysis revealed three distinct antigenic protein patterns among the recent isolates, differing from 1984 isolates.
• Monoclonal antibody labeling showed limited reactivity, with isolate 081 being unreactive to all tested antibodies.
• AvaII digestion patterns of the 16S rRNA gene differed between Kentucky isolates and those from Illinois, Virginia, and Ohio.

Conclusions:

• The study identified distinct variants of Ehrlichia risticii based on morphological, antigenic, and genetic differences.
• These findings highlight significant biological diversity within E. risticii populations, impacting disease understanding and diagnostics.