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Identification of Brucella canis Seroreactive Proteins and Serology Assay Development


Fast-Track proposals will not be accepted.
Number of anticipated awards: 1
Budget (total costs):
Phase I: up to $150,000 for up to 12 months

Several species of the genus Brucella, Gram-negative, facultative intracellular coccobacilli, cause brucellosis in animals and humans. Whereas the zoonotic potential of Brucella melitensis, B. abortus, and B. suis is well known, and manifests itself in a disease burden of more than 500,000 annual human cases worldwide, the extent to which B. canis is transmitted from infected dogs to humans is unclear. Human brucellosis infections are difficult to diagnose and difficult to treat. There is no human vaccine available in the United States. B. melitensis, B. abortus, and B. suis are Select Agents, with a low infectious dose, which makes brucellosis one of the most frequent laboratory-acquired infections. Serological assays are a critical tool for diagnosis of brucellosis and for monitoring exposed personnel for evidence of infection. However, there are currently no
B. canis serological tests available to detect and measure the humoral immune response in humans.
Brucella strains such as B. melitensis, B. abortus, and B. suis have an O-specific polysaccharide as part of the outer membrane lipopolysaccharide and are designated as “smooth” strains. In contrast, other strains such as B. canis, B. ovis, and the live attenuated bovine vaccine strain B. abortus RB51, are missing the O-specific polysaccharide from the outer
membrane lipopolysaccharide and are designated as “rough” strains. The lack of this specific lipopolysaccharide means that standard Brucella serological assays do not work for “rough” strains. The identification of specific antigens of rough Brucella strains is a prerequisite for the development of serological assays.
Project Goals
The goal of this project is to develop assays for detection of antibodies against rough Brucella strains such as B. canis and bovine vaccine strain B. abortus RB51, which are known human pathogens. Presently, we are not able to offer serological diagnosis to infected patients, or monitoring to exposed individuals.
Phase I Activities and Expected Deliverables
Phase I: Screen entire proteome of Brucella species using sera from canine and human infections to identify specific B. canis and B. abortus RB51 antigens that are recognized by antibodies. If successful, antigens (e.g., proteins) identified in Phase I will be used in Phase II to develop a diagnostic serologic assay.
For Successful Phase I Awardees ONLY (Expected Phase II Deliverables)
Develop optimized serodiagnostic assays with high specificity and sensitivity based on the Phase I analysis of the humoral immune response to B. canis. Current Brucella serology assays lack specificity and sensitivity and are not able to detect infection by rough strains such as B. canis. Depending on data from Phase I, combinations of antigens could be used to detect infection by both smooth and rough strains.
At present, we are unable to gauge the burden of B. canis human infections or risk associated with exposure to B. canis infected animals because we have no diagnostic tools for serological surveillance. We are also not able to measure the antibody response in potentially exposed occupational risk groups such as veterinarians, physicians, clinical microbiologists, dog breeders, dog kennel and animal shelter workers, and in pet owners whose dogs develop B. canis infection. Comprehensive screening of the B. canis proteome for specific antigenic targets would allow for development of serological methods to detect and respond to human exposure cases and strengthen public health in the US and globally by gaining insight into B. canis dog-to-human transmission patterns and risk factors.
Commercialization Potential
The worldwide burden of brucellosis has been estimated at 500,000 cases/year; however, this is likely underestimated due to the lack of optimal diagnostics. All presently available assays to detect host antibody responses to exposure and infection by smooth Brucella strains are lacking specificity and sensitivity. Inactivated whole cell preparations or LPS extracts serve as crude capture antigens with high levels of cross-reactivity. There are no serology assays available for detection of human antibody responses against rough Brucella strains. There is a critical need to find specific, immunogenic markers whose epitopes can be analyzed, synthesized and developed into optimized serological diagnostic assays. Development and use of

such assays would be of interest to public health laboratories, private diagnostic laboratories, and academic brucellosis researchers.

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