Virusinfections of the respiratory tract in horses - Etiology, epidemiology, clinical manfestation,vaccination and defense - Part 1: Equine Influenza and Equine Herpesviruses

Abstract

Within the respiratory diseases of horses infectious and non infectious factors are of etiological evidence. Within the infectious agents viruses with special offinty to the epithelium of the respiratory tract are of epidemiological importance. Equine influenza A viruses (H7/N7, H3/N8) remain a major cause of respiratory diseases in horses worldwide. The influenza H3/N8 subtypes continue to change their hemagglutinin through antigenic drift. This and the increased international transport of horses resulted in repeated worldwide outbreaks of the H3/N8 disease. Virus shedding even from vaccinated horses spreads the viruses rapidly within susceptible horse populations. This is of significant financial impact. The H3/N8 viruses are endemic in Europe and U.S.A., disease control relies mainly on mandatory vaccination of sport horses. The success however of those programmes is largely dependent on commercially available vaccines, their relevant virus antigens and efficacy in providing clinical and/or virological protection and the correctness and intensity of vaccination programmes. These different situations and programmes , also especially in different horse populations are presented and discussed. Another group of viruses with relevance to the equine respiratory tract are the Equine Herpesviruses (EHVJ. The equine alphaherpesviruses EHV4 and EHV1 as well as the gammaherpesviruses EHV2 and EHV5 are causative for obligat persistent (latent) infections in upto 80% of the investigated horses worldwide. All together foals and young horses are the target animals for clinical manifest infections of the upper respiratory tract with the participation of one or more members of the am. EHVs at the same time in the same organism. The clinical as well financial impact of these infections is not comparable to those following Flu infections. In elder horses the clinically inapparent infections are dominant. Existing vaccines against EHV1 and/or EHV4 and mandatory vaccination programmes can not interrupt the latent stage of these infections and they didn't contribute to significant epidemilogical and/or clinical improvement in the vaccinated horses. The etiological importance of EHV2 and EHV5 for clinical manifestations at the respiratory tract is uncertain. EHV2 infections of the horse' eye followed by ceratocon junctivitis spf. has been confirmed, upper and lower respiratory tract EHV2 and EHV5 infections, often together with bacterial infections are described , the multinodular pulmonary fibrosis, caused by EHV5, is er suspicion. The reduced ability of the present EHV1/EHV4- vaccines requires more potent vaccines. Strict hygienic measurements and management strategies are necessary in controlling these infections.