The desired impacts of my research program into equine bacterial disease are the development and application of effective and safe vaccines, sensitive and specific diagnostics, and improved understanding of epizootiologic features of value in prevention and management of outbreaks. Success in these efforts requires identification and molecular characterization of bacterial components involved in virulence and protective immune responses, elucidation of mechanisms and modes of induction of protective immunity, and analysis of the host-parasite interaction at the microscopic and ultra structural levels.
The need for a more effective and safe vaccine against equine strangles has driven our efforts to identify proteins of Streptococcus equi that stimulate protective immune responses. The nearly complete genomic sequence of S. equi (Sanger, http://www.sanger.ac.uk) has greatly accelerated the pace of this discovery, and we are now evaluating a large number of novel surface-exposed or secreted proteins in immunization/challenge trials and in experimental infections with defined mutants. Comprehensive morphologic and histochemical studies of Dr. Pawan Kumar, visiting Clay Fellow, on the equine tonsillar complex have provided key information on entry of S. equi and on the location and stage of infection at which protective immunity is active in resistant horses. Since immunity to strangles is not stimulated by S. zooepidemicus, an organism almost identical to the clonal S. equi, Sergey Artiushin is sequencing the genome of S. zooepidemicus W60 to identify proteins unique to S. equi and differences in regulatory pathways. In a related project, Raksha Tiwari, a PhD student, is sequencing the genome of P9, a temperate bacteriophage of S. equi that Jon Spanier and I isolated in 1976. Studies of the genomic sequence of S. equi have revealed that genes for some virulence factors are phage encoded and that acquisition of bacteriophage was a key event in formation of the more virulent S. equi from its S. zooepidemicus ancestor. Outcomes of our research on S. equi include a PCR test for detection of S. equi in clinical samples, several ELISAs for assay of specific antibodies, and development of a genetically labeled avirulent vaccine strain.
Pneumonia secondary to influenza virus infection or to high temperature stress (summer pneumonia) has been shown to be due to invasion of lung by a single clone of S. zooepidemicus selected from the indigenous tonsillar flora.
Abortion and recurrent uveitis are the most familiar clinical manifestations of leptospira infection of horses. The very high levels and multiple specificities of antibodies in sera of recently aborted mares have been valuable tools for detection of leptospira proteins up regulated at body temperature or expressed only during infection. Commercial vaccines prepared from Leptospira spp. cultured at 30°C are deficient in these important immunogens, and so new generation vaccines are likely to contain one or more of these proteins. My laboratory has characterized 3 novel host-induced proteins and shared in characterization of a fourth. Useful by-products of these studies have been development of ELISA’s to differentiate vaccine from infection responses and improved PCR methodology for detection of leptospira in horse urine by Sergey Artiushin. Finally, Ashutosh Verma, a PhD student in my group has characterized several novel leptospira proteins uniquely expressed and immunogenic in uveitic eyes. This information will have implications regarding the composition of new generation leptospira vaccines for use in species susceptible to uveitis.
Dr. John Timoney, Keeneland Association Chair in Equine Veterinary Science
(859) 257-4757, email@example.com
Maxwell H. Gluck Equine Research Center, University of Kentucky.