Equine Vaccines
Investigators:
Background:
Horses remain a valuable agricultural and companion animal species and hyper-immunized horses are used in serum production for the prevention of human disease. Vaccination is common and the horse industry has a strong interest in the development of safer and more effective vaccines for this species. Many of our industrial partners market equine vaccines that they are constantly trying to improve upon. These companies also engaged in the development of new vaccines. VIDO has the staff and facilities to efficiently undertake vaccine studies in unbroken horses and has been doing so for the last 15 years. These resources, in combination with VIDO’s scientific expertise and laboratory capacity, provides industry with a unique partner for basic research and post-licensing studies.
Recent Results
Over that past five years, we have conducted a number of studies on the efficacy of equine influenza vaccines using a unique challenge model developed at VIDO. Of particular note was a large vaccine study carried out in collaboration with investigators at the University of Wisconsin, comparing the antibody responses of young and mature horses to North American registered. multivalent vaccines (Influenza, Equine Herpes Virus, Tetanus, and Equine Encephalomyelitis) and protection following influenza virus challenge. This study demonstrated marked differences in immune responses among horses and vaccines and identified the product that produced the greatest protection against experimental influenza challenge. We also examined the onset of immunity and protection provided by a commercial, cold adapted modified live intra-nasal vaccine and showed protection of naïve horses as early as four days post-vaccination.
More recently, studies conducted at VIDO have shown that inclusion of CpG in inactivated influenza vaccines and several vaccines against recombinant bacterial antigens shortens the onset of protective immune responses, increases the magnitude of total IgG and immunoglobulin isotype titres and increases the duration of measurable titres to these antigens beyond what can be achieved using adjuvants that are commonly used in commercial vaccine formulations. Initial challenge trials, suggest that the use of CpG in killed equine influenza vaccines may also result in improved clinical protection following live virus challenge, although further work is required to confirm this finding.
Rhodococcus equi is a facultative, intracellular pathogen that causes granulomatous pneumonia in foals and immunecompromised humans. We have developed a challenge model for this disease in foals and have assessed the immunogenicity of two experimental vaccines, a riboflavin auxotroph and recombinant VapA (virulence associated protein) vaccine in neonatal foals. Single, intrabronchial administration of the auxotroph primed an antibody response in vaccinated foals that became evident following challenge but did not provide clinical protection against disease. This potential for basing a vaccine on this technology is currently being explored by a commercial vaccine manufacturer. In a more recent study we showed that following one vaccination of foals with the rVapA vaccine resulted in significant increases in serum antibody (IgG, IgGa, IgGb and IgGt) which increased further after a second vaccination. Increases in PBMC, antigen specific proliferation responses were observed after the second vaccination. The vaccine also primed interferon gamma expression in response to challenge but did not appear to provide clinical protection in this model. The results of this challenge were encouraging and are likely to lead to further work.
