INTRODUCTION

Equine influenza is a highly contagious virus of horses which infects the respiratory tract. It is widespread throughout the world, and outbreaks have occurred in Europe, North- and South America, Asia, South-Africa and Australia; only Iceland and New Zealand have never had an outbreak. The disease occurs regularly in Europe and North-America. Equine influenza is self-limiting, and although the disease can be severe in naïve populations, in populations in which equine influenza occurs regularly clinical symptoms are usually not severe and it is rarely fatal.