Research Accomplishment Reports 2007

The Effect of Aging on the Immune Response of Horses

D.W. Horohov, T. Chambers
Department of Veterinary Sciences

 

Project Description

Horses over 20 years of age constitute about 15% of the equine population and many remain actively involved in equestrian sports and in reproductive capacities as stallions and brood mares. Advancing age in horses, as with other species, is eventually associated with a decline in body condition, muscle tone and immune function.  One of the marked changes in immune function that has been reported for the older horse is decreased responsiveness to vaccination.  Nevertheless, there are no specific recommendations regarding the vaccination of older horses and ponies.  It is also unclear how susceptible older horses may be to some of the infectious agents against which vaccination is routinely practiced.  In particular, the relative susceptibility of the older horse to equine influenza virus is unknown.  Given that most older horses have likely been exposed to equine influenza virus throughout their lives, either through vaccination or infection, or both, it is reasoned that they retain specific immunity to this virus.  However, studies in humans have clearly shown that immunity to influenza viruses wanes with age leading to increased susceptibility amongst the elderly.  Indeed, it is the elderly population that is targeted for annual influenza vaccination.  To address whether aged horses exhibit a similar susceptibility to equine influenza virus, we performed an infectious challenge study using a group of young and aged horses.

Impact

Our results indicated that the older horse is susceptible to this infection, though clinical signs were not as severe in the older horses as those seen in younger horses.  Nevertheless, the older horses exhibited both cytokine and antibody responses similar to younger horses post-challenge and, most importantly, shed virus for several days post-infection.  As such, it is clear that vaccination of the older horse to prevent equine influenza virus infection is necessary.  However, given the fact that old horses do not respond well to conventional vaccines, future work will be needed to determine the optimal vaccination strategy for the older horse.

Publications

Adams, A.A., Breathnach, C.C., Sturgill, T., Chambers, T., and Horohov, D.W. (2007). Characterization of the immunological and physiological response of aged horses to equine influenza infection. (abstract) The 8th International Veterinary Immunology Symposium, Ouro Preto, Brazil, 2007 (ER091).

Adams, A.A., Katepalli, M., Kohler, K., Reedy, S., Stilz, J.P., Vick, M.M., Fitzgerald, B.P., and Horohov, D.W. (2007). The contribution of body condition score and percent body fat to the inflammatory response in aged horses.  (abstract) The 8th International Veterinary Immunology Symposium, Ouro Preto, Brazil, 2007 (ER090).

Adams, A.A., Breathnach, C.C., Sturgill, T., Chambers, T., and Horohov, D.W. (2007). Characterization of the immunological and physiological response of aged horses to equine influenza infection.  Proceedings of the 88th Conference of Research Workers in Animal Disease, Chicago, Illinois, 2007 (#114).