The Response of Ponies to Myxovirus influenzaeA-Equi-2*

Twenty-five ponies were infected intranasally with Myxovirus iufluenzaeA-Equi-2. Their response to this challenge was evaluated with respect to the prechallenge serum and nasal antibody titres against the infecting virus. Out of the 25 ponies, 21 had a serum haemagglutination inhibition (HI) antibody titre of 1/5 or greater at the time of challenge, and 10 of these ponies resisted infection. Those ponies with HI titres of 1/80 or greater all resisted infection. All serologically negative ponies were susceptible. Ten ponies in the group had nasal neutralizing, as well as serum HI, antibody. Nine of these 10 ponies resisted infection. It was not possible to decide statistically if the presence of detectable nasal antibody was a better marker of resistance to infection than was a serum HI antibody titre of 1/80 or greater.