Targeted disruption of a specific gene and its subsequent restoration in obligate intracellular bacteria remains extremely challenging due to their absolute requirement for residence inside a host cell to replicate. Here, targeted allelic exchange mutations were created to inactivate two genes and then to restore one of the two genes of a rickettsial pathogen, Ehrlichia chaffeensis. These methods were then also successfully utilized in Ehrlichia canis and Anaplasma phagocyophilum. The resultant mutated pathogens are useful in immunogenic compositions for reducing the incidence of or severity of infection with ricksettsial pathogens.

Provided herein are immunogenic compositions that may be used, in some aspects, to induce an immune response against an Ehrlichia such as Ehrlichia cams. In some embodiments, the immunogenic composition comprises an E. canis bacterin and/or adjuvant, such as for example an emulsion or liposomal adjuvant. Related methods such as for diagnosis of or vaccination against ehrlichiosis are also provided.

Provided herein are immunogenic compositions that may be used, in some aspects, to induce an immune response against an Ehrlichia such as Ehrlichia cams. In some embodiments, the immunogenic composition comprises an E. canis bacterin and/or adjuvant, such as for example an emulsion or liposomal adjuvant. Related methods such as for diagnosis of or vaccination against ehrlichiosis are also provided.

Neorickettsia helminthoeca is an obligate intra-cytoplasmic bacterium that causes salmon poisoning disease (SPD), an acute, febrile, fatal disease of dogs. Disclosed are compositions and methods for the immunodetection of N. helminthoeca in a canine subject. Also disclosed are immunogenic N. helminthoeca peptides that can be used in a vaccine for N. helminthoeca.

The present invention discloses novel isolates of Neorickettsia risticii, compositions comprising such isolates, vaccines and methods for using such vaccines against Potomac Horse Fever.

Provided herein are compositions and methods for detection and treatment of Rocky Mountain spotted fever (“RMSF”). The compositions specifically detect Rickettsia rickettsii and do not cross-react with other Rickettsia species providing rapid and accurate detection and diagnosis of RMSF.

Provided herein are compositions and methods for detection and treatment of Rocky Mountain spotted fever (“RMSF”). The compositions specifically detect Rickettsia rickettsii and do not cross-react with other Rickettsia species providing rapid and accurate detection and diagnosis of RMSF.

Provided herein are chimeric polypeptides that may be used, e.g., for the diagnosis of or vaccination against Ehrlichia chaffeensis and/or Ehrlichia canis.

Provided herein are chimeric polypeptides that may be used, e.g., for the diagnosis of or vaccination against Ehrlichia chaffeensis and/or Ehrlichia canis.

The present invention concerns gp36 immunoreactive compositions for E. canis and gp 47 immunoreactive compositions for E. chaffeensis. In particular, epitopes for E. canis gp36 and E. chaffeensis gp 47 are disclosed. In certain embodiments, the immunoreactive compositions comprise tandem repeats having carbohydrate moieties.